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Advanced automotive fault diagnosis tom denton Document Transcript

  • 1. Advanced Automotive Fault Diagnosis
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  • 3. Advanced AutomotiveFault DiagnosisSecond editionTom Denton BA, MSAE, MIRTE, Cert. Ed.Associate Lecturer, Open University, UK AMSTERDAM • BOSTON • HEIDELBERG • LONDON • OXFORD • NEW YORK PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Butterworth-Heinemann is an imprint of Elsevier
  • 4. Elsevier Butterworth-HeinemannLinacre House, Jordan Hill, Oxford OX2 8DP, UK30 Corporate Drive, Suite 400, Burlington MA 01803, USAFirst published 2000Reprinted 2002, 2003, 2004Second edition 2006Copyright © 2006, Tom Denton. Published by Elsevier Ltd. All rights reserved.The right of Tom Denton to be identified as the author of this work has been asserted inaccordance with the Copyright, Designs and Patents Act 1988No part of this publication may be reproduced, stored in a retrieval system or transmitted in any formor by any means electronic, mechanical, photocopying, recording or otherwise without the priorwritten permission of the publisherPermission may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford,UK: phone (ϩ44) (0) 1865 843830; fax (ϩ44) (0) 1865 853333; email: permissions@elsevier.com.Alternatively you can submit your request online by visiting the Elsevier web site at http://elsevier.com/locate/permissions, and selecting Obtaining permission to use Elsevier materialNoticeNo responsibility is assumed by the publisher for any injury and/or damage to persons or property asa matter of products liability, negligence or otherwise, or from any use or operation of any methods,products, instructions or ideas contained in the material herein. Because of rapid advances in themedical sciences, in particular, independent verification of diagnoses and drug dosages should be madeBritish Library Cataloguing in Publication DataA catalogue record for this book is available from the British LibraryLibrary of Congress Cataloging-in-Publication DataA catalog record for this book is available from the Library of CongressISBN-13: 978-0-75-066991-7ISBN-10: 0-75-066991-8 For information on all Butterworth-Heinemann publications visit our website at www.books.elsevier.comTypeset by Charon Tec Ltd, Chennai, Indiawww.charontec.comPrinted and bound in the United Kingdom06 07 08 09 10 9 8 7 6 5 4 3 2 1
  • 5. ContentsPreface ixIntroduction to the second edition xiAcknowledgments xiiiGlossary xv1 Introduction 11.1 ‘If it ain’t broke, don’t fix it!’ 11.2 Safe working practices 11.3 Terminology 21.4 Report writing 32 Diagnostic techniques 62.1 Introduction 62.2 Diagnostic process 62.3 Diagnostics on paper 82.4 Mechanical diagnostic techniques 92.5 Electrical diagnostic techniques 122.6 Fault codes 172.7 Systems 182.8 On- and off-board diagnostics 202.9 Data sources 213 Tools and equipment 253.1 Basic equipment 253.2 Oscilloscopes 283.3 Scanners/fault code readers 303.4 Engine analysers 324 Oscilloscope diagnostics 404.1 Introduction 404.2 Sensors 404.3 Actuators 494.4 Ignition system 544.5 Other components 584.6 Summary 605 On-board diagnostics 615.1 On-board diagnostics – a first perspective 615.2 What is on-board diagnostics? 635.3 Petrol/gasoline on-board diagnostic monitors 665.4 On-board diagnostics – a second perspective 745.5 Summary 846 Sensors and actuators 866.1 Introduction 866.2 Sensors 866.3 Actuators 94
  • 6. vi Contents7 Engine systems 987.1 Introduction 987.2 Engine operation 987.3 Diagnostics – engines 1017.4 Fuel system 1037.5 Diagnostics – fuel system 1067.6 Introduction to engine management 1087.7 Ignition 1087.8 Diagnostic – ignition systems 1167.9 Emissions 1207.10 Diagnostics – emissions 1227.11 Fuel injection 1227.12 Diagnostics – fuel injection systems 1267.13 Diesel injection 1277.14 Diagnostics – diesel injection systems 1307.15 Engine management 1327.16 Diagnostics – combined injection and fuel control systems 1387.17 Engine management and faultfinding information 1437.18 Air supply and exhaust systems 1447.19 Diagnostics – exhaust and air supply 1477.20 Cooling 1487.21 Diagnostics – cooling 1507.22 Lubrication 1517.23 Diagnostics – lubrication 1537.24 Batteries 1557.25 Diagnosing battery faults 1567.26 Starting 1597.27 Diagnosing starting system faults 1637.28 Charging 1637.29 Diagnosing charging system faults 1678 Chassis systems 1698.1 Brakes 1698.2 Diagnostics – brakes 1728.3 Anti-lock brakes 1748.4 Diagnostics – anti-lock brakes 1778.5 Traction control 1788.6 Diagnostics – traction control 1808.7 Steering and tyres 1818.8 Diagnostics – steering and tyres 1868.9 Suspension 1908.10 Diagnostics – suspension 1959 Electrical systems 1979.1 Electronic components and circuits 1979.2 Multiplexing 2009.3 Lighting 2039.4 Diagnosing lighting system faults 2079.5 Auxiliaries 2099.6 Diagnosing auxiliary system faults 2149.7 In car entertainment (ICE) security and communications 2169.8 Diagnosing ICE, security and communication system faults 2199.9 Body electrical systems 2219.10 Diagnosing body electrical system faults 2259.11 Instrumentation 2269.12 Diagnosing instruments system faults 230
  • 7. Contents vii9.13 Heating, ventilation and air conditioning (HVAC) 2319.14 Diagnostics – HVAC 2379.15 Cruise control 2399.16 Diagnostics – cruise control 2409.17 Air bags and belt tensioners 2419.18 Diagnostics – air bags and belt tensioners 24410 Transmission systems 24710.1 Manual transmission 24710.2 Diagnostics – manual transmission 25110.3 Automatic transmission 25310.4 Diagnostics – automatic transmission 25611 Conclusion, web resources and developments 26011.1 Introduction 26011.2 Web contacts 26011.3 Future developments in diagnostic systems 26211.4 Software 26311.5 Summary 265Index 267
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  • 9. PrefaceThe aspect I still enjoy most about working on may need to listen to a rumbling noise as the carvehicles is being able to diagnose a fault that has corners, for another you may need to interpret anbeaten others! This skill takes a few years to oscilloscope waveform or a diagnostic troubledevelop but it is worth the effort. Diagnostic work code.is much like that of a detective solving a difficult Vehicles continue to become more complicated,crime, all the clues are usually there – if you know particularly in the area of electronics. The needwhere to look. I think it was Sherlock Holmes (a for technicians with good diagnostic skills there-fictional detective if you have never heard of fore remains. This could be you and you shouldhim!) who said: be paid well! Look on the bright side of having complicated When you have eliminated all which is technology on vehicles – fewer ‘home mechanics’ impossible, then whatever remains, however and more work for you and me! improbable, must be the truth.This is a great thought for a diagnostic technician Tom Dentonto keep in mind. 2006 To help you learn ‘where to look’ for the cluesand to eliminate the impossible, this book com- PS. Comments and contributions are welcome atbines some aspects of automotive technology cov- my web site: www.automotive-technology.co.uk.ered in my other books. However, it goes much You will also find lots of useful information,further with a new approach to the art of diag- updates, news and details about my other booksnostics as a science. as well as automotive training software and web The skills needed to be a good diagnostic links.technician are many and varied. For one job you
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  • 11. Introduction to the second editionThe book has grown! But then it was always going management and all engine electrics (batteries,to, because the complexity of automotive systems etc.) are now part of the Engines chapter.has grown and the associated diagnostic skills The book is ideal for all MV qualifications, inmust follow. particular: The main change for this edition is that I have ● City & Guilds 4101 Technical Certificates andincluded two completely new chapters. The first NVQsis all about on-board diagnostics (OBD) and the ● IMI Technical Certificates and NVQssecond covers oscilloscope diagnostics in some ● Level 4 diagnostic unitsdetail. Both of these subjects are very relevant to ● BTEC/Edexcel National and Higher Nationalall aspects of the automotive repair trade, light or qualificationsheavy vehicle. ● International MV qualifications such as C&G I have tried wherever possible to make the con- 3905tent relevant to all types of vehicle whether used ● ASE certification in the USin the UK, USA or anywhere else in the world. ● Supplementary reading for MV degree levelAfter all, most vehicles have an engine that makes course.the wheels go round – even if the steering wheelchanges sides… Of course, you may already be qualified and just There has been a significant rationalisation of need a few pointers!motor vehicle qualifications in the UK since the You may also simply want to learn more aboutfirst edition. The result is that this book has how your car works – and how to fix it when itbecome even more appropriate because of the doesn’t!higher technical content. The order of the material I hope you enjoy this book, but most of all I hopehas been changed a bit so that it lines up more it helps you to become a better diagnostic techni-with current qualifications. For example, engine cian – something you should be very proud to be.
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  • 13. AcknowledgmentsI am very grateful to the following companies Robert Bosch GmbHwho have supplied information and/or permis- Robert Bosch UKsion to reproduce photographs and/or diagrams: Rover Saab UKAA Photo Library Scandmec UKAutodata Snap-on ToolsAutologic Data Systems Sun Electric UKBMW UK Sykes-PickavantBosch Press Photos Valeo UKEberspaecher GmbH ZF ServomaticFord Motor CompanyGenRad Many if not all the companies here have goodHella UK web pages. You will find a link to them from myInstitute of Road Transport Engineers site. Thanks again to the listed companies. If IJaguar Cars have used any information or mentioned a com-Kavlico Corp pany name that is not noted here, please acceptLucas Service my apologies and acknowledgments.LucasVarity An extra thanks to Dave Rogers (AVL) andMazda Cars UK Alan Malby (Ford Motor Company) for theirNGK Spark Plugs UK kind assistance with the OBD chapter.Pioneer Radio Also, if I forget to mention my family: Vanda,Renault UK Malcolm and Beth, I will be in trouble…Ricardo
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  • 15. Glossary Authors Note: To keep the glossary to a reason- EC: engine control able size, I decided to limit the entries to useful ECL: engine coolant level acronyms that are specified by the society of automo- ECM: engine control module tive engineers (SAE) and on-board diagnostic version ECT: engine coolant temperature two (OBD2) recommendations. I have provided free access to online glossaries (UK, US and Spanish) that EEPROM: electrically erasable program- include several thousand words. mable read only memory www.automotive-technology.co.uk EFE: early fuel evaporation EGR: exhaust gas recirculationTwo key words never to forget: EGRT: EGR temperature EI: electronic ignitionSymptom(s): What the user/operator/repairer EM: engine modification of the system (vehicle or what- EPROM: erasable programmable read ever) notices only memoryFault: An error in the system that EVAP: evaporative emission system causes symptom(s) FC: fan controlOBD2/SAE acronyms FEEPROM: flash electrically erasable pro-ABS: antilock brake system grammable read only memoryA/C: air conditioning FF: flexible fuelAC: air cleaner FP: fuel pumpAIR: secondary air injection FPROM: flash erasable programmableA/T: automatic transmission or read only memory transaxle FT: fuel trimAP: accelerator pedal FTP: federal test procedureBϩ: battery positive voltage GCM: governor control moduleBARO: barometric pressure GEN: generatorCAC: charge air cooler GND: groundCFI: continuous fuel injection H2O: waterCL: closed loop HC: hydrocarbonCKP: crankshaft position sensor HO2S: heated oxygen sensorCKP REF: crankshaft reference HO2S1: upstream heated oxygen sensorCMP: camshaft position sensor HO2S2: up or downstream heatedCMP REF: camshaft reference oxygen sensorCO: carbon monoxide HO2S3: downstream heated oxygenCO2: carbon dioxide sensorCPP: clutch pedal position HVS: high voltage switchCTOX: continuous trap oxidizer HVAC: heating ventilation and air con-CTP: closed throttle position ditioning systemDEPS: digital engine position sensor IA: intake airDFCO: deceleration fuel cut-off mode IAC: idle air controlDFI: direct fuel injection IAT: intake air temperatureDLC: data link connector IC: ignition control circuitDTC: diagnostic trouble code ICM: ignition control moduleDTM: diagnostic test mode IFI: indirect fuel injectionEBCM: electronic brake control IFS: inertia fuel shutoff module I/M: inspection/maintenanceEBTCM: electronic brake traction IPC: instrument panel cluster control module ISC: idle speed control
  • 16. xvi GlossaryKOEC: key on, engine cranking PSP: power steering pressureKOEO: key on, engine off PTOX: periodic trap oxidizerKOER: key on, engine running RAM: random access memoryKS: knock sensor RM: relay moduleKSM: knock sensor module ROM: read only memoryLT: long term fuel trim RPM: revolutions per minuteMAF: mass airflow sensor SC: superchargerMAP: manifold absolute pressure SCB: supercharger bypass sensor SDM: sensing diagnostic modeMC: mixture control SFI: sequential fuel injectionMDP: manifold differential pressure SRI: service reminder indicatorMFI: multi-port fuel injection SRT: system readiness testMIL: malfunction indicator lamp ST: short term fuel trimMPH: miles per hour TB: throttle bodyMST: manifold surface temperature TBI: throttle body injectionMVZ: manifold vacuum zone TC: turbochargerNOX: oxides of nitrogen TCC: torque converter clutchNVRAM: non-volatile random access TCM: transmission or transaxle con- memory trol moduleO2S: oxygen sensor TFP: throttle fluid pressureOBD: on-board diagnostics TP: throttle positionOBD I: on-board diagnostics generation TPS: throttle position sensor one TVV: thermal vacuum valveOBD II: on-board diagnostics, second TWC: three way catalyst generation TWC ϩ OC: three way ϩ oxidation catalyticOC: oxidation catalyst converterODM: output device monitor VAF: volume airflowOL: open loop VCM: vehicle control moduleOSC: oxygen sensor storage VR: voltage regulatorPAIR: pulsed secondary air injection VS: vehicle sensorPCM: powertrain control module VSS: vehicle speed sensorPCV: positive crankcase ventilation WOT: wide open throttlePNP: park/neutral switch WU-TWC: warm up three way catalyticPROM: program read only memory converterPSA: pressure switch assembly
  • 17. 1Introduction1.1 ‘If it ain’t broke, don’tfix it!’1.1.1 What is needed to findfaults?Finding the problem when complex automotivesystems go wrong is easy, if you have the neces-sary knowledge. This knowledge is in two parts:● understanding of the system in which the problem exists;● the ability to apply a logical diagnostic routine.It is also important to be clear about two defini- Figure 1.1 Diagnostics in actiontions:● symptom(s) what the user/operator/repairer Figure 1.1 shows a diagnostic procedure in of the system (vehicle or whatever) notices; action!● fault the error in the system that causes the symptom(s). 1.1.2 Heavy or light vehicles? ‘If it is not broken then do not go to the troubleof repairing it,’ is the translation of this main sec- An important note about diagnostics is that thetion heading! It’s a fair comment but if a system is general principles or techniques can be appliednot operating to its optimum then it should be to any system, physical or otherwise. As far asrepaired. This is where the skills come in to play. heavy or light vehicles are concerned then this isIt is necessary to recognise that something is not definitely the case. As discussed earlier, there isoperating correctly by applying your knowledge a need for knowledge of the particular system,of the system, and then by applying this know- but diagnostic skills are transferable.ledge further and combining it with the skills ofdiagnostics, to be able to find out why. Each main chapter of this book includes a 1.2 Safe workingbasic explanation of the vehicle system followed practicesby diagnostic techniques that are particularlyappropriate for that area. Examples of fault-finding charts are also included. In the main, ref- 1.2.1 Introductionerences will be to generic systems rather than to Safe working practices in relation to diagnosticspecific vehicles or marques. For specific details procedures and indeed any work on a vehicle areabout a particular vehicle or system the manufac- essential – for your safety as well as that of others.turer’s information is the main source. Alterna- You only have to follow two rules to be safe:tively ‘Autodata’ produce a fine range of books; ● use your common sense – don’t fool about;visit www.autodata.com for more details. ● if in doubt – seek help. The knowledge requirement and the necessityfor diagnostic skills are further illustrated in the Further, always wear appropriate personal protect-next chapter. ive equipment (PPE) when working on vehicles.
  • 18. 2 Advanced automotive fault diagnosis The following section lists some particular 1.3 Terminologyrisks when working with electricity or electricalsystems, together with suggestions for reducingthem. This is known as risk assessment. 1.3.1 Introduction The terminology included in the following tables1.2.2 Risk assessment and is provided to ensure that we are talking the same language. These tables are provided just as areduction simple reference source.The following table notes some identified risksinvolved with working on vehicles. It is by nomeans exhaustive but serves as a good guide. 1.3.2 Diagnostic terminologyIdentified risk Reducing the risk Symptom The effect of a fault noticed by the driver, user or technicianBattery acid Sulphuric acid is corrosive so always use good Fault The root cause of a symptom/problem PPE – in this case overalls and if necessary Diagnostics The process of tracing a fault by means of its rubber gloves. A rubber apron is ideal, as are symptoms, applying knowledge and analysing goggles if working with batteries a lot test resultsElectric shock Ignition HT (high tension, which simply means Knowledge The understanding of a system that is required high voltage) is the most likely place to suffer a to diagnose faults shock, up to 25 000 V is quite normal. Use insulated tools if it is necessary to work on HT Logical A step by step method used to ensure nothing circuits with the engine running. Note that high procedure is missed voltages are also present on circuits containing Report A standard format for the presentation of windings due to back emf (electromotive force) results as they are switched off; a few hundred volts is common. Mains supplied power tools and their leads should be in good condition and using an earth leakage trip is highly recommended 1.3.3 General terminologyExhaust gases Suitable extraction must be used if the engine is running indoors. Remember it is not just System A collection of components that carry out a the carbon monoxide (CO) that might make function you ill or even kill you, other exhaust compon- ents could cause asthma or even cancer Efficiency This is a simple measure of any system. It can be scientific for example if the power outFire Do not smoke when working on a vehicle. of a system is less then the power put in, its Fuel leaks must be attended to immediately. percentage efficiency can be determined Remember the triangle of fire – (heat/fuel/ (Pout/Pin ϫ 100%). This could, for example, be oxygen) – don’t let the three sides come given as 80%. In a less scientific example, a together vehicle using more fuel than normal is said toMoving loads Only lift what is comfortable for you; ask for be inefficient help if necessary and/or use lifting equipment. As a general guide, do not lift on your own if Noise Emanation of sound from a system that is it feels too heavy! either simply unwanted or is not the normal sound that should be producedRaising or Apply brakes and/or chock the wheels andlifting vehicles when raising a vehicle on a jack or drive on Active Any system that is in operation all the time lift. Only jack under substantial chassis and (steering for example) suspension structures. Use axle stands in case Passive A system that waits for an event before it is the jack fails activated (an air bag is a good example)Running Do not wear loose clothing; good overalls Short circuit An electrical conductor is touching somethingengines are ideal. Keep the keys in your possession that it should not be (usually another con- when working on an engine to prevent others ductor or the chassis) starting it. Take extra care if working near Open circuit A circuit that is broken (a switched off switch running drive belts is an open circuit)Short circuits Use a jump lead with an in-line fuse to prevent High In relation to electricity, this is part of a damage due to a short when testing. resistance circuit that has become more difficult for the Disconnect the battery (earth lead off first and electricity to get through. In a mechanical back on last) if any danger of a short exists. A system a partially blocked pipe would have very high current can flow from a vehicle bat- a resistance to the flow of fluid tery, it will burn you as well as the vehicleSkin problems Use a good barrier cream and/or latex gloves. Worn This word works better with further additions Wash skin and clothes regularly such as: worn to excess, worn out of toler- ance, or even, worn, but still within tolerance!
  • 19. Introduction 3Quote To make an estimate of or give exact informa- Test criteria tion on the price of a part or service. A quota- tion may often be considered to be legally Define the limits within which the test was car- binding ried out. For example, temperature range or speedEstimate A statement of the expected cost of a certain settings. job (e.g. a service or repairs) An estimate is normally a best guess and is not legally binding Facilities/resourcesDodgy, Words often used to describe a system orknackered or component, but they mean nothing! Get used State or describe what equipment was used. For@#%&*! to describing things so that misunderstandings example: ‘A “Revitup” engine dynamometer, are eliminated model number C3PO was used for the consump- tion test’.1.4 Report writing Test procedures Explain here exactly what was done to gain the1.4.1 Introduction results. In this part of the report it is very import- ant not to leave out any details.As technicians you may be called on to producea report for a customer. Also, if you are involvedin research of some kind it is important to be able Measured resultsto present results in a professional way. The fol- Present the results in a way that is easy to inter-lowing sections describe the main headings that a pret. A simple table of figures may be appropriate.report will often need to contain together with an If the trend of the results or a comparison is import-example report based on the performance testing ant, a graph may be better. Pictures of results orof a vehicle alternator. oscilloscope waveforms may be needed. If neces- Laying out results in a standard format is the sary a very complex table of results from whichbest way to ensure that all the important and you draw out a few key figures, could be presentedrequired aspects of the test have been covered. as an appendix. You should also note the accuracyKeep in mind that the report should convey of any figures presented (Ϯ0.5% for example).clearly to another person what has been done.Further, a ‘qualified’ person should be able to Analysis of resultsextract enough information to be able to repeat This is the part where you should comment onthe test – and check your findings! Use clear sim- the results obtained. For example, if say a fuelple language remembering that in some cases the consumption test was carried out on two vehicles,intended audience may not be as technically a graph comparing one result to the other may becompetent as you are. appropriate. Comments should be added if nec- essary, such as any anomaly that could have affected the results (change of wind direction for1.4.2 Main headings of a example).reportThe following suggestions for the headings of a Conclusions/comments/professional report will cover most requirements observationsbut can of course be added to or subtracted from Note here any further tests that may be necessary.if necessary. After each heading I have included Conclude that device X does perform better thanbrief notes on what should be included. device Y – if it did! If appropriate, add observa- tions such as how device Y performed betterContents under the set conditions, but under other circum-If the report is more than about five pages, a list stances the results could have been different.of contents with page numbers will help the Comment on the method used if necessary.reader find his/her way through it. ForecastIntroduction If necessary comment on how the ‘item’ testedExplain the purpose of what has been done and will continue to perform based on the exist-set the general scene. ing data.
  • 20. 4 Advanced automotive fault diagnosisAppendices Test proceduresDetailed pages of results that would ‘clog up’ the The alternator was run for 10 minutes atmain report or background material such as 3000 rev/min and the load adjusted to cause anleaflets relating to the test equipment. output of 30 A. This was to ensure that it was at a nominal operating temperature. The normal fan was kept in place during the test.1.4.3 Example report Speed was then increased to 6000 rev/min and the load adjusted to achieve the maximumAn example report is presented here relating to a possible output. The load was further adjusted assimple alternator test where its actual output is to required to keep the maximum possible output inbe compared to the rated output. Minimal details case the load resistance changed due to tempera-are included so as to illustrate the main points. ture. Measurements were taken every 30 seconds for a period of 10 minutes.IntroductionA ‘Rotato’ 12 V alternator was tested under nor- Measured resultsmal operating conditions to check its maximum Speed held constant at 6000 (Ϯ200) rev/min.output. The manufacturer’s specifications stated Room temperature (18°C).that the alternator, when hot, should produce 95 Aat 6000 rev/min. Time (Ϯ1 s) 0 30 60 90 120 150 180 210 240 270 Output 101 100 99 99 98 98 98 98 98 98 (Ϯ0.2 A)Test criteria● Start at room temperature. Time 300 330 360 390 420 450 480 510 540 570 600● Run alternator at 3000 rev/min, 30 A output (Ϯ1 s) for 10 minutes. Output 97 97 96 96 96 96 96 96 96 96 96● Run alternator at 6000 rev/min, maximum (Ϯ0.2 A) output. Check reading every 30 seconds for 10 minutes. To ensure that the alternator output had stabilised● Run alternator at 6000 rev/min, maximum out- it was kept running for a further 20 minutes at put for a further 20 minutes to ensure that out- full output. It continued to hold at 96 A. put reading is stable. Analysis of resultsFacilities/resources Figure 1.2 shows the results in graphical format.A ‘Krypton’ test bench model R2D2 was used todrive the alternator. The test bench revcounterwas used and a ‘Flake’ digital meter fitted with a Conclusions200 A shunt was used to measure the output. A The manufacturer’s claims were validated. Thevariable resistance load was employed. device exceeded the rated output by 6% at the startFigure 1.2 Results presented in graphical format
  • 21. Introduction 5of the test and under continuous operation at full further after prolonged operation. Further tests areload, continued to exceed the rated output by 1%. necessary to check this. Overall the device per- The maximum duration of this test was 20 min- formed in excess of its rated output.utes. It is possible, however, that the device would (Sign and date the report)increase in temperature and the output may fall Tom Denton, Wednesday, 25th Jan. 2006 Knowledge check questions To use these questions, you should first try to answer them without help but if necessary, refer back to the content of the chapter. Use notes, lists and sketches as appropriate to answer them. It is not neces- sary to write pages and pages of text! 1. State the meaning of the terms ‘fault’ and ‘symptom’. 2. Explain how to reduce the risk of a short circuit when testing electrical systems. 3. List the main headings that could be used for a standard report. 4. State the two main pieces of knowledge necessary to diagnose faults. 5. Describe the potential dangers of running an engine in an enclosed space without exhaust extraction.
  • 22. 2Diagnostic techniques2.1 Introduction but introduce more faults into the system in the process. I would suggest you learn your own strengths2.1.1 Logic and weaknesses; you may be confident and goodDiagnostics or faultfinding is a fundamental part at dealing with mechanical system problems butof an automotive technician’s work. The subject less so when electronics is involved. Of courseof diagnostics does not relate to individual areas of you may be just the opposite of this.the vehicle. If your knowledge of a vehicle sys- Remember that diagnostic skill is in twotem is at a suitable level, then you will use the parts – the knowledge of the system and the abil-same logical process for diagnosing the fault, ity to apply diagnostics. If you do not yet fullywhatever the system. understand a system – leave it alone!2.1.2 InformationInformation and data are available for carrying 2.2 Diagnostic processout many forms of diagnostic work. The datamay come as a book or on CD. This information 2.2.1 Six-stage processis vital and will ensure that you find the fault – A key checklist – the six stages of fault diagnosis –particularly if you have developed the diagnostic is given in Table 2.1.skills to go with it. Faultfinding charts and spe- Here is a very simple example to illustrate thecific examples are presented in later chapters. diagnostic process. The reported fault is exces- The general type of information available is as sive use of engine oil.follows: 1. Question the customer to find out how much● engine diagnostics, testing and tuning; oil is being used (is it excessive?).● servicing, repairs and times; 2. Examine the vehicle for oil leaks and blue● fuel and ignition systems and carburettor; smoke from the exhaust.● auto electrics; 3. If leaks are found the engine could still be● ABS diagnostics; burning oil but leaks would be a likely cause.● component location; 4. A compression test, if the results were accept-● body repairs, tracking and tyres. able, would indicate the leak to be the most likely fault. Clean down the engine and run for a while. The leak will show up better.2.1.3 Where to stop? 5. Change a gasket or seal, etc.This is one of the most difficult skills to learn. It 6. Run through an inspection of the vehicle sys-is also one of the most important. The secret is tems particularly associated with the engine.twofold:● know your own limitations – it is not possible Table 2.1 to be good at everything;● leave systems alone where you could cause 1. Verify the fault 2. Collect further information more damage or even injury – for example air 3. Evaluate the evidence bag circuits. 4. Carry out further tests in a logical sequence 5. Rectify the problemOften with the best of intentions, a person new 6. Check all systemsto diagnostics will not only fail to find the fault
  • 23. Diagnostic techniques 7 Double check the fault has been rectified and that you have not caused any further problems. Verify the faultThe stages of faultfinding will be used exten-sively to illustrate how a logical process can beapplied to any situation. Collect further information2.2.2 The art of diagnosticsThe knowledge needed for accurate diagnosticsis in two parts: Evaluate the1. understanding of the system in which the evidence problem exists;2. having the ability to apply a logical diagnostic routine. No Carry out furtherThe knowledge requirement and use of diagnostic Fault located? tests in a logicalskills can now be illustrated with a very simple sequenceexample. After connecting a hose pipe and turningon the tap, no water comes out of the end! Your Yesknowledge of this system tells you that watershould come out providing the tap is on, because Rectify the faultthe pressure from a tap pushes water through thepipe, and so on. This is where your diagnosticskills become essential. The following stages arenow required.1. Confirm that no water is coming out by look- Check all systems ing down the end of the pipe!2. Does water come out of the other taps, or did it come out of this tap before you connected Figure 2.1 Diagnostic routine the hose?3. Consider what this information tells you; for example here, but electrical systems will be example, if the answer is ‘Yes’ the hose must covered in detail in later chapters. Remember that be blocked or kinked. the diagnostic procedure can be applied to any4. Walk the length of the pipe looking for a kink. problem, mechanical, electrical or even personal!5. Straighten out the hose. However, let’s assume that the reported fault6. Check that water now comes out and that no with the vehicle is overheating. As is quite com- other problems have been created. mon in many workshop situations that’s all theMuch simplified I accept, but the procedure you information we have to start with. Now workhave just followed made the hose work and it is through the six stages.also guaranteed to find a fault in any system. It iseasy to see how it works in connection with a hose ● Stage 1 Take a quick look to check for obvi-pipe and I’m sure anybody could have found that ous problems such as leaks, broken drive beltsfault (well most people anyway)! The higher skill or lack of coolant. Run the vehicle and con-is to be able to apply the same logical routine to firm that the fault exists. It could be the tem-more complex situations. The routine (Table 2.1) perature gauge for example.is represented by Figure 2.1. The loop will con- ● Stage 2 Is the driver available to give moretinue until the fault is located. I will now explain information? For example, does the engineeach of these steps further in relation to a more overheat all the time or just when workingrealistic automotive workshop situation – not that hard? Check records, if available, of previousgetting the hose to work is not important! work done to the vehicle. Often electrical faults are considered to be the ● Stage 3 Consider what you now know. Doesmost difficult to diagnose – but this is not true. this allow you to narrow down what the causeI will use a vehicle cooling system fault as an of the fault could be? For example, if the vehicle
  • 24. 8 Advanced automotive fault diagnosis overheats all the time and it had recently had ‘pulling the car to pieces’, it will often save a a new cylinder head gasket fitted, would you great deal of time. In other words, some of the be suspicious about this? Don’t let two and diagnostic work can be done ‘on paper’ before two make five, but do let it act as a pointer. we start on the vehicle. To illustrate this, the next Remember that in the science of logical diag- section lists symptoms for three separate faults nostics, two and two always makes four! on a car and for each of these symptoms, three However, until you know this for certain then possible faults. All the faults are possible but in play the best odds to narrow down the fault. each case choose the ‘most likely’ option.● Stage 4 The further tests carried out would now be directed by your thinking at stage three. You don’t yet know if the fault is a leaking head 2.3.2 Examples gasket, the thermostat stuck closed or some other problem. Playing the odds, a cooling sys- Symptoms Possible faults tem pressure test would probably be the next A The brake/stop lights are 1. Two bulbs and 12 LEDs test. If the pressure increases when the engine reported not operating. On blown is running then it is likely to be a head gasket or checking it is confirmed 2. Auxiliary systems relay similar problem. If no pressure increase then that neither of the two open circuit move on to the next test and so on. After each bulbs or the row of 3. Brake light switch not test go back to stage 3 and evaluate what you high-mounted LEDs is closing operating as the pedal is know, not what you don’t know! pressed. All other systems● Stage 5 Let’s assume the problem was a work correctly thermostat stuck closed – replace it and top up B An engine fitted with full 1. Fuel pump output the coolant, etc. management system tends to pressure low● Stage 6 Check that the system is now work- stall when running slowly. 2. Idle control valve sticking ing. Also check that you have not caused any It runs well under all other 3. Engine speed sensor wire conditions and the reported loose further problems such as leaks or loose wires. symptom is found to be This example is simplified a little, but like the intermittent hose pipe problem it is the sequence that mat- C The off side dip beam 1. Two bulbs blown ters, particularly the ‘stop and think’ at stage 3. headlight not operating. This 2. Main lighting fusible link It is often possible to go directly to the cause of is confirmed on examination blown the fault at this stage, providing that you have an and also noted is that the 3. Short circuit between off adequate knowledge of how the system works. off side tail light does not side tail and dip beam work lights2.2.3 Summary The most likely fault for example A, is number 3.I have introduced the six-stage process of diag- It is possible that all the lights have blown butnostics, not so it should necessarily be used as a unlikely. It could not be the auxiliary relaychecklist but to illustrate the process that must be because this would affect other systems.followed. Much more detail is required still, par- For example B, the best answer would be num-ticular in relation to stages 3 and 4. The purpose ber 2. It is possible that the pump pressure is lowof this set process is to ensure that ‘we’ work in a but this would be more likely to affect operationparticular, logical way. under other conditions. A loose wire on the engine I would like to stress the need for a logical speed sensor could cause the engine to stall but itprocess again – with a quotation! ‘Logic is the would almost certainly cause misfire under otherbeginning of wisdom not the end.’ (Spock to conditions.Valeris, Star Trek II) The symptoms in C would suggest answer 1. The short circuit suggested as answer 3 would be more likely to cause lights and others to stay on2.3 Diagnostics on paper rather that not work, equally the chance of a short between these two circuits is remote if not impos- sible. If the lighting fusible link were blown then2.3.1 Introduction none of the lights would operate.This section is again a way of changing the way The technique suggested here relates to stagesyou approach problems on a vehicle. The key 1 to 3 of the ‘the six stages of fault diagnosis’message is that if you stop and think before process. By applying a little thought before even
  • 25. Diagnostic techniques 9taking a screwdriver to the car, a lot of time can 2.4.2 Noise, vibration andbe saved. If the problems suggested in the previ- harshnessous table were real we would at least now be ableto start looking in the right area for the fault. Noise, vibration and harshness (NVH) concerns have become more important as drivers have become more sensitive to these issues. Drivers2.3.3 How long is a piece of have higher expectations of comfort levels. Noise,string? vibration and harshness issues are more noticeable due to reduced engine noise and better insulationYes I know, twice the distance from the middle in general. The main areas of the vehicle that pro-to one end! What I am really getting at here duce NVH are:though is the issue about what is a valid reading/measurement and what is not – when compared ● tyres;to data. For example if the ‘data book’ says the ● engine accessories;resistance of the component should be between ● suspension;60 and 90 ⍀, what do you do when the measured ● driveline.value is 55 ⍀? If the measured value was 0 ⍀ or1000 ⍀ then the answer is easy – the component It is necessary to isolate the NVH into its specificis faulty! However, when the value is very close area(s) to allow more detailed diagnosis. Ayou have to make a decision. In this case (55 ⍀) it road test as outlined later is often the bestis very likely that the component is serviceable. method. The decision over this type of issue is difficult The five most common sources of non-axleand must in many cases be based on experience. noise are exhaust, tyres, roof racks, trim andAs a general guide however, I would suggest that mouldings, and transmission. Ensure that none ofif the reading is in the right ‘order of magnitude’, the following conditions is the cause of the noisethen the component has a good chance of being before proceeding with a driveline strip down andOK. By this I mean that if the value falls within diagnosis.the correct range of 1s, 10s, 100s or 1000s etc. then 1. In certain conditions, the pitch of the exhaustit is probably good. may sound like gear noise or under other con- Do notice that I have ensured that words or ditions like a wheel bearing rumble.phrases such as ‘probably’, ‘good chance’ and 2. Tyres can produce a high pitched tread whine‘very likely’ have been used here! This is not just or roar, similar to gear noise. This is particu-to make sure I have a get out clause; it is also to larly the case for non-standard tyres.illustrate that diagnostic work can involve ‘playing 3. Trim and mouldings can cause whistling orthe best odds’ – as long as this is within a logical whining noises.process. 4. Clunk may occur when the throttle is applied or released due to backlash somewhere in the2.4 Mechanical diagnostic driveline. 5. Bearing rumble sounds like marbles beingtechniques tumbled.2.4.1 Check the obvious first! 2.4.3 Noise conditionsStart all hands on diagnostic routines with ‘handand eye checks’. In other words look over the Noise is very difficult to describe. However, thevehicle for obvious faults. For example, if auto- following are useful terms and are accompaniedmatic transmission fluid is leaking on to the floor by suggestions as to when they are most likely tothen put this right before carrying out complicated occur.stall tests. Here are some further suggestions that ● Gear noise is typically a howling or whiningwill at some point save you a lot of time. due to gear damage or incorrect bearing pre-● If the engine is blowing blue smoke out of the load. It can occur at various speeds and driv- exhaust – consider the worth of tracing the ing conditions, or it can be continuous. cause of a tapping noise in the engine! ● ‘Chuckle’ is a rattling noise that sounds like a● When an engine will not start – check that stick held against the spokes of a spinning bicy- there is fuel in the tank! cle wheel. It usually occurs while decelerating.
  • 26. 10 Advanced automotive fault diagnosis● Knock is very similar to chuckle though it carried out. Of course this does not apply if the may be louder and occurs on acceleration or condition could be dangerous or the vehicle will deceleration. not start!Check and rule out tyres, exhaust and trim items Establish a route that will be used for all diag-before any disassembly to diagnose and correct nosis road tests. This allows you to get to knowgear noise. what is normal and what is not! The roads selected should have sections that are reasonably smooth, level and free of undulations as well as2.4.4 Vibration conditions lesser quality sections needed to diagnose faults that only occur under particular conditions. AClicking, popping or grinding noises may be road that allows driving over a range of speeds isnoticeable at low speeds and be caused by the best. Gravel, dirt or bumpy roads are unsuitablefollowing: because of the additional noise they produce.● inner or outer CV joints worn (often due to If a customer complains of a noise or vibration lack of lubrication so check for split gaiters); on a particular road and only on a particular road,● loose drive shaft; the source of the concern may be the road surface.● another component contacting a drive shaft; Test the vehicle on the same type of road.● damaged or incorrectly installed wheel bear- Make a visual inspection as part of the prelim- ing, brake or suspension component. inary diagnosis routine prior to the road test; note anything that does not look right.The following may cause vibration at normalroad speeds: 1. Tyre pressures, but do not adjust them yet. 2. Leaking fluids.● out-of-balance wheels; 3. Loose nuts and bolts.● out-of-round tyres. 4. Bright spots where components may be rub-The following may cause shudder or vibration bing against each other.during acceleration: 5. Check the luggage compartment for unusual loads.● damaged power train/drive train mounts;● excessively worn or damaged out-board or Road test the vehicle and define the condition in-board CV joints. by reproducing it several times during the road test. During the road test recreate the following The cause of noise can often be traced by first conditions.looking for leaks. A dry bearing or joint will pro-duce significant noise. 1. Normal driving speeds of 20 to 80 km/h (151. Inspect the CV joint gaiters (boots) for cracks, to 50 mph) with light acceleration, a moan- tears or splits. ing noise may be heard and possibly a vibra-2. Inspect the underbody for any indication of tion is felt in the front floor pan. It may get grease splatter near the front wheel half shaft worse at a certain engine speed or load. joint boots. 2. Acceleration/deceleration with slow accel-3. Inspect the in-board CV joint stub shaft bear- eration and deceleration, a shake is sometimes ing housing seal for leakage at the bearing noticed through the steering wheel seats, front housing. floor pan, front door trim panels, etc.4. Check the torque on the front axle wheel hub 3. High speed a vibration may be felt in the retainer. front floor pan or seats with no visible shake, but with an accompanying sound or rumble, buzz, hum, drone or booming noise. Coast with2.4.5 Road test the clutch pedal down or gear lever in neutralA vehicle will produce a certain amount of noise! and engine idling. If vibration is still evident, itSome noise is acceptable and may be audible at may be related to wheels, tyres, front brakecertain speeds or under various driving condi- discs, wheel hubs or wheel bearings.tions such as on a new road. 4. Engine rev/min sensitive a vibration may Carry out a thorough visual inspection of the be felt whenever the engine reaches a particu-vehicle before carrying out the road test. Keep in lar speed. It may disappear in neutral coasts.mind anything that is unusual. A key point is to Operating the engine at the problem speednot repair or adjust anything until the road test is while the vehicle is stationary can duplicate
  • 27. Diagnostic techniques 11 the vibration. It can be caused by any compon- Noise description Possible source ent, from the accessory drive belt to the clutch or torque converter, which turns at engine Tap Valve clearances out of adjustment, speed when the vehicle is stopped. cam followers or cam lobes worn5. Noise and vibration while turning clicking, Rattle A loose component, broken piston popping or grinding noises may be due to the ring or component following: damaged CV joint; loose front wheel Light knock Small end bearings worn, cam or half shaft joint boot clamps; another component cam follower contacting the half shaft; worn, damaged or Deep knock or thud Big end bearings worn incorrectly installed wheel bearing; damaged Rumble Main bearings worn power train/drive train mounts. Slap Worn pistons or bores Vibration Loose or out of balance After a road test, it is often useful to do a simi- componentslar test on a lift. When carrying out the shake Clatter Broken rocker shaft or brokenand vibration diagnosis or engine accessory vibra- piston ringstion diagnosis on a lift, observe the following Hiss Leak from inlet or exhaustprecautions. manifolds or connections● If only one drive wheel is allowed to rotate, Roar Air intake noise, air filter missing, exhaust blowing or a seized speed must be limited to 55 km/h (35 mph) viscous fan drive indicated on the speedometer. This is because Clunk Loose flywheel, worm thrust bear- the actual wheel speed will be twice that indi- ings or a loose front pulley/damper cated on the speedometer. Whine Power steering pump or alternator● The suspension should not be allowed to hang bearing free. If a CV joint were run at a high angle, Shriek Dry bearing in an ancillary extra vibration as well as damage to the seals component and joints could occur. Squeal Slipping drive belt Support the front suspension lower arm as farout-board as possible. This will ensure that thevehicle is at its correct ride height. The pro- 2.4.7 Sources of engine noisecedure is outlined by the following steps. The following table is a further guide to engine1. Raise and support the vehicle. noise. Possible causes are listed together with the2. Explore the speed range of interest using the necessary repair or further diagnosis action as road test checks as previously discussed. appropriate.3. Carry out a coast down (overrun) in neutral. If the vehicle is free of vibration when operating Sources of engine Possible cause Required action at a steady indicated speed and behaves very noise differently in drive and coast, a transmission Misfiring/backfiring Fuel in tank has Determine concern is likely. wrong octane/ which type of Note, however, that a test on the lift may pro- cetane number, fuel was last put or is wrong type in the tankduce different vibrations and noises than a road of fueltest because of the effect of the lift. It is not Ignition system Check theunusual to find a vibration on the lift that was not faulty ignition systemnoticed during the road test. If the condition Engine temperature Check thefound on the road can be duplicated on the lift, too high engine cooling systemcarrying out experiments on the lift may save a Carbon deposits Remove thegreat deal of time. in the combustion carbon deposits chamber start to by using fuel2.4.6 Engine noises glow and cause additives and misfiring driving theHow do you tell a constant tapping from a rattle? vehicle carefullyWorse still, how do you describe a noise in a Timing incorrect, Check the which causes timingbook? I’ll do my best! Try the following table as misfiring in thea non-definitive guide to the source or cause of intake/exhaustengine or engine ancillary noises. system.
  • 28. 12 Advanced automotive fault diagnosisValve train faulty Valve clearance too Adjust valve cause enough current to flow to at best give you a large due to faulty clearance if false reading and at worst damage an ECU – so bucket tappets or possible and incorrect renew faulty don’t use it! adjustment of valve bucket tappets – A digital multimeter is ideal for all forms of clearance check cam testing. Most have an internal resistance in excess condition of 10 M⍀. This means that the current they draw Valve timing Check the valve is almost insignificant. An LED test lamp or a incorrectly adjusted, timing and valves and pistons adjust if logic probe is also acceptable. are touching necessary Timing belt broken Check timing belt or damaged and check pistons 2.5.3 Generic electrical testing and valves for procedure damage – renew any faulty parts The following procedure is very generic but withEngine Pistons Disassemble the a little adaptation can be applied to anycomponents Piston rings engine and electrical system. Refer to manufacturer’s recom-faulty Cylinder head gasket check mendations if in any doubt. The process of check- Big end and/or main components bearing journals ing any system circuit is broadly as follows.Ancillary Engine Check that allcomponents components or components are Auxiliary systems diagnostic chart ancillary secure, tighten/ components loose adjust as required Start or broken Renew if broken Hand and eye checks (loose wires, loose switches and other obvious faults)– all connections clean and tight.2.5 Electrical diagnostic Check batterytechniques Check motor (including linkages) or actuator or bulb(s) – visual check2.5.1 Check the obvious first! Fuse continuity – (do not trust yourStart all hands on diagnostic routines with ‘hand eyes) check voltage at both sides with a meter or a test lampand eye checks’. In other words look over thevehicle for obvious faults. For example, if the bat-tery terminals are loose or corroded then put this Voltage supplies at the Check item withright before carrying out complicated voltage No device/motor/ actuator/ Yes separate fused supplyreadings. Here are some further suggestions that bulb(s) are correct? if possible before condemningwill at some point save you a lot of time.● A misfire may be caused by a loose plug lead – it is easier to look for this than interpret the ignition waveforms on a scope. No If used does the relay Yes click (this means the relay has● If the ABS warning light stays on – look to see operated it is not necessarily making contact)? if the wheel speed sensor(s) are covered in mud or oil. Supply to switch – Supplies to relay (terminal battery volts 30 for example) – battery volts2.5.2 Test lights and analoguemeters – warning! Supply out of the switch and to the relay – Feed out of the relay (terminal 87 for example) – battery volts) battery voltsA test lamp is ideal for tracing faults in say a Voltage supply to the lightlighting circuit because it will cause a current to Relay earth connection – within 0.5 V of the battery note also that the relay mayflow which tests out high resistance connections. have a supply and that theHowever, it is this same property that will dam- control switch may make the earth connection Earth circuit (continuity orage delicate electronic circuits – so don’t use it voltage) – 0 ohms or 0 Vfor any circuit that contains an electronic control Endunit (ECU). Even an analogue voltmeter can
  • 29. Diagnostic techniques 13 V1 V2 to connect a bulb or test lamp across the blown fuse and switch on the circuit. The bulb will light V3 because on one side it is connected to the supply for the fuse and on the other side it is connected V4 to earth via the fault. Now disconnect small sec- VS tions of the circuit one at a time until the test lamp goes out. This will indicate the particular circuit section that has shorted out.Figure 2.2 Volt drop testing 2.5.6 On and off load tests On load means that a circuit is drawing a current. Off load means it is not! One example where this2.5.4 Volt drop testing may be an issue is when testing a starter circuit. Battery voltage may be 12 V off load but onlyVolt drop is a term used to describe the difference 9 V when on load.between two points in a circuit. In this way we can A second example is the supply voltage to thetalk about a voltage drop across a battery (normally positive terminal of an ignition coil via a highabout 12.6 V) or the voltage drop across a closed resistance connection (corroded switch terminalswitch (ideally 0 V but may be 0.1 or 0.2 V). for example). With the ignition on and the vehicle The first secret to volt drop testing is to remem- not running, the reading will almost certainly beber a basic rule about a series electrical circuit: battery voltage because the ignition ECU switchesThe sum of all volt drops around a circuit always off the primary circuit and no volt drop will showadds up to the supply. up. However, if the circuit were switched on (with The second secret is to ensure that the circuit a fused jumper lead if necessary) a lower readingis switched on and operating – or at least the cir- would result showing up the fault.cuit should be ‘trying to operate’! In Figure 2.2 this means that V1 ϩ V2 ϩV3 ϭ Vs. When electrical testing, therefore, andif the battery voltage measured as say 12 V, a 2.5.7 Black box techniquereading of less than 12 V at V2 would indicate a The technique that will be covered here is knownvolt drop between the terminals of V1 and/or V3. as ‘black box faultfinding’. This is an excellentLikewise the correct operation of the switch, that technique and can be applied to many vehicleis it closes and makes a good connection, would systems from engine management and ABS tobe confirmed by a very low reading on V1. cruise control and instrumentation. What is often described as a ‘bad earth’ (when As most systems now revolve around an ECU,what is meant is a high resistance to earth), could the ECU is considered to be a ‘black box’, inequally be determined by the reading on V3. other words we know what it should do but how To further narrow the cause of a volt drop it does it is irrelevant! Any colour, so long as it’sdown a bit, simply measure across a smaller area. black [Henry Ford (1920s)]. I doubt that he wasThe voltmeter V4, for example, would only assess referring to ECUs though …the condition of the switch contacts. Figure 2.3 shows a block diagram that could be used to represent any number of automobile electrical or electronic systems. In reality the2.5.5 Testing for short circuits arrows from the ‘inputs’ to the ECU and from the ECU to the ‘outputs’ are wires. Treating theto earth ECU as a ‘black box’ allows us to ignore its com-This fault will normally blow a fuse – or burn out plexity. The theory is that if all the sensors andthe wiring completely! To trace a short associated wiring to the ‘black box’ are OK, allcircuit is very different from looking for a high the output actuators and their wiring are OK andresistance connection or an open circuit. The volt the supply/earth connections are OK, then thedrop testing above will trace an open circuit or a fault must be the ‘black box’. Most ECUs arehigh resistance connection. very reliable, however, and it is far more likely My preferred method of tracing a short, after that the fault will be found in the inputs orlooking for the obvious signs of trapped wires, is outputs.
  • 30. 14 Advanced automotive fault diagnosis Wires disconnected Input 1 from ECU Component 2 Output 1 such as a sensor Ω2 3 ECU 2 Ω1 ECU 4 3 5 With wires disconnectedFigure 2.3 System block diagram Figure 2.4 Ohmmeter tests Normal faultfinding or testing techniques can Warningbe applied to the sensors and actuators. For exam- The circuit supply must always be off when car-ple, if an ABS system uses four inductive type rying out ohmmeter tests.wheel speed sensors, then an easy test is to meas-ure their resistance. Even if the correct value werenot known, it would be very unlikely for all four to 2.5.9 Flight recorder testsbe wrong at the same time so a comparison can be It is said that the best place to sit in an aeroplane ismade. If the same resistance reading is obtained on the black box flight recorder! Well, apart fromon the end of the sensor wires at the ECU then the black box usually being painted bright orangealmost all of the ‘inputs’ have been tested with just so it can be found after a crash, my reason for men-a few ohmmeter readings. tioning it is to illustrate how the flight recorder The same technique will often work with ‘out- principle can be applied to automotive diagnostics.puts’. If the resistance of all the operating wind- Most hand-held scopes now have flight recordings in say a hydraulic modulator were the same, facilities. This means that they will save the signalthen it would be reasonable to assume the figure from any probe connection in memory for laterwas correct. play back. The time duration will vary depending Sometimes, however, it is almost an advantage on the available memory and the sample speed butnot to know the manufacturer’s recommended this is a very useful feature.readings. If the ‘book’ says the value should be As an example, consider an engine with anbetween 800 and 900 ⍀, what do you do when intermittent misfire that occurs only under load.your ohmmeter reads 905 ⍀? Answers on a post- If a connection is made to the suspected compon-card please … (or see Section 2.3.3). ent (coil HT output for example), and the vehicle Finally, don’t forget that no matter how is road tested, the waveforms produced can becomplex the electronics in an ECU, they will examined afterwards.not work without a good power supply and an Many engine (and other system) ECUs haveearth! built in flight recorders in the form of self- diagnostic circuits. If a wire breaks loose causing a misfire but then reconnects the faulty circuit2.5.8 Sensor to ECU will be ‘remembered’ by the ECU.methodThis technique is simple but very useful. Figure 2.4shows a resistance test being carried out on a 2.5.10 Faultfinding by luck!component. ⍀1 is a direct measure of its resist- Or is it logic? If four electric windows stoppedance whereas ⍀2 includes the condition of the working at the same time, it would be very unlikelycircuit. If the second reading is the same as the that all four motors had burned out. On the otherfirst then the circuit must be in good order. hand if just one electric window stopped working,
  • 31. Diagnostic techniques 15Figure 2.5 Faultfinding by luck!then it may be reasonable to suspect the motor. It familiar with a few key wire colours and terminalis this type of reasoning that is necessary when numbers when diagnosing electrical faults. Asfaultfinding. However, be warned it is theoretic- seems to be the case for any standardisation aally possible for four motors to apparently burn number of colour code systems are in operation!out all at the same time! For reference purposes I will just mention two. Using this ‘playing the odds’ technique can save Firstly, the British Standard system (BS AUtime when tracing a fault in a vehicle system. For 7a: 1983): this system uses 12 colours to deter-example, if both stop lights do not work and every- mine the main purpose of the cable and tracerthing else on the vehicle is OK, I would suspect the colours to further refine its use. The main colourswitch (stages 1 to 3 of the normal process). At this uses and some further examples are given in thestage though, the fault could be anywhere – even following table.two or three blown bulbs. None-the-less a quicktest at the switch with a voltmeter would prove thepoint. Now, let’s assume the switch is OK and it Colour Symbol Destination/useproduces an output when the brake pedal is pushed Brown N Main battery feeddown. Testing the length of wire from the front to Blue U Headlight switch to dip switchthe back of the vehicle further illustrates how ‘luck’ Blue/White UW Headlight main beamcomes into play. Blue/Red UR Headlight dip beam Figure 2.5 represents the main supply wire Red R Side light main feed Red/Black RB Left hand side lights and no. platefrom the brake switch to the point where the wire Red/Orange RO Right hand side lights‘divides’ to each individual stop light (the odds Purple P Constant fused supplysay the fault must be in this wire). For the purpose Green G Ignition controlled fused supplyof this illustration we will assume the open circuit Green/Red GR Left side indicatorsis just before point ‘I’. The procedure continues Green/White GW Right side indicators Light Green LG Instrumentsin one of the two following ways. Either: White W Ignition to ballast resistor● guess that the fault is in the first half and test White/Black WB Coil negative Yellow Y Overdrive and fuel injection at point F; Black B All earth connections● we were wrong! Guess that the fault is in the Slate S Electric windows first half of the second half and test at point I; Orange O Wiper circuits (fused)● we were right! Check at H and we have the Pink/White KW Ballast resistor wire fault … on test number THREE; Green/Brown GN Reverse Green/Purple GP Stop lightsor: Blue/Yellow UY Rear fog light● test from A to K in a logical sequence of tests;● we would find the fault … On test number Secondly there is a ‘European’ system used NINE! by a number of manufacturers and based broadlyYou may choose which method you prefer! on the following table. Please note there is no correlation between the ‘Euro’ system and the2.5.11 Colour codes and British Standard colour codes. In particular note the use of the colour brown in each system! Afterterminal numbers some practice with the use of colour code sys-This section is really more to be used as a refer- tems the job of the technician is made a lot easierence source. It is useful, however, to become when faultfinding an electrical circuit.
  • 32. 16 Advanced automotive fault diagnosis System-Connection (FSC). The system was devel-Colour Symbol Destination/use oped to assist in vehicle development and pro-Red Rt Main battery feed duction processes. However, it is also very usefulWhite/Black Ws/Sw Headlight switch to dip in helping the technician with fault finding. Many switch of the function codes are based on the DIN sys-White Ws Headlight main beamYellow Ge Headlight dip beam tem. Note that earth wires are now black! TheGrey Gr Side light main feed system works as follows.Grey/Black Gr/Sw Left hand side lightsGrey/Red Gr/Rt Right hand side lights 31S-AC3A || 1.5 BK/RDBlack/Yellow Sw/Ge Fuel injection Function:Black/Green Sw/Gn Ignition controlled supplyBlack/White/Green Sw/Ws/Gn Indicator switch 31 ϭ ground/earthBlack/White Sw/Ws Left side indicatorsBlack/Green Sw/Gn Right side indicators S ϭ additionally switched circuitLight Green LGn Coil negativeBrown Br Earth System:Brown/White Br/Ws Earth connections AC ϭ headlamp levellingBlack Sw ReverseBlack/Red Sw/Rt Stop lights Connection:Green/Black Gn/Sw Rear fog light 3 ϭ switch connection A ϭ branch A system now in use almost universally is theterminal designation system in accordance with Size:DIN 72 552. This system is to enable easy and 1.5 ϭ 1.5 mm2correct connections to be made on the vehicle,particularly in after sales repairs. Note that the Colour:designations are not to identify individual wires BK ϭ black (determined by function 31)but to define the terminals of a device. Listedbelow are some of the most popular numbers. RD ϭ red stripe The new Ford colour codes table is as follows:1 Ignition coil negative4 Ignition coil high tension Code Colour15 Switched positive (ignition switch output)30 Input from battery positive BK Black31 Earth connection BN Brown49 Input to flasher unit BU Blue49a Output from flasher unit GN Green50 Starter control (solenoid terminal) GY Grey53 Wiper motor input LG Light-green54 Stop lamps OG Orange55 Fog lamps PK Pink56 Headlamps RD Red56a Main beam SR Silver56b Dip beam VT Violet58L Left side lights WH White58R Right side lights YE Yellow61 Charge warning light85 Relay winding out86 Relay winding input Ford system codes are as follows.87 Relay contact input (change over relay)87a Relay contact output (break) Letter Main system Examples87b Relay contact output (make)L Left side indicators D Distribution systems DE ϭ earthR Right side indicators A Actuated systems AK ϭ wiper/washerC Indicator warning light (vehicle) B Basic systems BA ϭ charging BB ϭ starting C Control systems CE ϭ power steering G Gauge systems GA ϭ level/pressure/ The Ford Motor Company now uses a circuit temperaturenumbering and wire identification system. This H Heated systems HC ϭ heated seatsis in use worldwide and is known as Function, L Lighting systems LE ϭ headlights
  • 33. Diagnostic techniques 17M Miscellaneous systems MA ϭ air bags fault in one of the components or its associatedP Power train control systems PA ϭ engine control circuit causes a code to be stored in the ECUW Indicator systems WC ϭ bulb failure memory. (‘indications’ not turn The codes may be described as ‘fast’ or ‘slow’. signals)X Temporary for future XS ϭ too much! Some ECUs produce both types. An LED, dash features warning light, scope or even an analogue voltmeter can be used to read slow codes. Normally, slow As a final point to this section it must be noted codes are output as a series of flashes that mustthat the colour codes and terminal designations then be interpreted by looking up the code in a faultgiven are for illustration only. Further reference code table. The slow codes are normally initiatedshould be made for specific details to the manu- by shorting two connections on the diagnostic plugfacturer’s information. and then switching the ignition on. Refer to detailed data before shorting any pins out! Fast codes can only be read by using a fault2.5.12 Back probing connectors code reader or scanner. Future ECUs will use fastJust a quick warning! If you are testing for a sup- codes. In the same way as we accept that a goodply (for example) at an ECU, then use the probes digital multimeter is an essential piece of testof your digital meter with care. Connect to the equipment, it is now necessary to consider a faultback of the terminals; this will not damage the code reader in the same way.connecting surfaces as long as you do not apply If a code reader is attached to the serial port onexcessive force. Sometimes a pin clamped in the the vehicle harness, fast and slow codes can betest lead’s crocodile/alligator clip is ideal for read out from the vehicle computer. These areconnecting ‘through’ the insulation of a wire either displayed in the form of a two, three orwithout having to disconnect it. Figure 2.6 shows four digit output code or in text format if soft-the ‘back probing’ technique. ware is used.2.6 Fault codes 2.6.2 Fault code examples A number of codes and descriptions are repro-2.6.1 Fast and slow duced below as an example of the detailed infor-Most modern vehicle management systems carry mation that is available from a self-diagnosisout self-diagnostic checks on the sensors and system. The data relates to the Bosch Motronic 1.7actuators that connect to the vehicle ECU(s). A Figure 2.6 Test the voltage at a connection with care
  • 34. 18 Advanced automotive fault diagnosisand 3.1. Fault code lists are available in publica- The first method is clearly recommended becausetions such as those by ‘Autodata’ and ‘Autologic’. disconnecting the battery will also ‘reset’ many other functions such as the radio code, the clockFCR Description code and even the learnt or adaptive functions in the ECUs.000 No faults found in the ECU001 Fuel pump relay or fuel pump relay circuit001 Crank angle sensor (CAS) or circuit (alternative code)002 Idle speed control valve circuit 2.7 Systems003 Injector number 1 or group one circuit004 Injector number 3 or circuit005 Injector number 2 or circuit 2.7.1 What is a system006 Injectors or injector circuit. System is a word used to describe a collection of012 Throttle position switch or circuit016 CAS or circuit related components which interact as a whole. A018 Amplifier to ECU amplifier circuit motorway system, the education system or com-019 ECU puter systems are three varied examples. A large023 Ignition amplifier number 2 cylinder or circuit system is often made up of many smaller systems024 Ignition amplifier number 3 cylinder or circuit which in turn can each be made up of smaller025 Ignition amplifier number 1 cylinder or circuit026 ECU supply systems and so on. Figure 2.7 shows how this can029 Idle speed control valve (ISCV) or circuit be represented in a visual form.031 Injector number 5 or circuit One further definition: A group of devices032 Injector number 6 or injector group two circuit serving a common purpose.033 Injector number 4 or circuit Using the systems approach helps to split036 Carbon filter solenoid valve (CFSV) or circuit037 Oxygen sensor (OS) or circuit extremely complex technical entities into more041 Mass airflow (MAF) sensor or circuit manageable parts. It is important to note, however,046 ECU that the links between the smaller parts and the048 Air conditioning (AC) compressor or circuit boundaries around them are also very important.050 Ignition amplifier cylinder number 4 or circuit System boundaries will overlap in many cases.051 Ignition amplifier cylinder number 6 or circuit054 ECU The modern motor vehicle is a complex sys-055 Ignition amplifier or circuit tem and in itself forms just a small part of a larger062 Electronic throttle control or circuit transport system. It is the capacity for the motor064 Ignition timing (electronic) vehicle to be split into systems on many levels067 Vehicle speed sensor (VSS) or circuit067 CAS or circuit which aids in both its design and construction.070 OS or circuit The systems approach helps in particular with073 Vehicle speed sensor (VSS) or circuit understanding how something works and, further,076 CO potentiometer (non-cat) how to go about repairing it when it doesn’t!077 Intake air temperature sensor (ATS) or circuit078 Engine coolant temperature sensor (CTS) or circuit081 Alarm system or circuit 2.7.2 Vehicle systems082 Traction control or circuit083 Suspension control or circuit Splitting the vehicle into systems is not an easy085 AC compressor or circuit task because it can be done in many different ways.100 ECU200 ECU A split between mechanical systems and electrical201 OS control or circuit systems would seem a good start. However, this202 ECU203 Ignition primary or circuit204 Electronic throttle control signal or circuit Engine Electrical300 Engine ABS2.6.3 ClearingFault codes can be cleared from the ECU mem-ory in two ways:● using the facilities of a fault code reader (scan- ner) to clear the memory; Complete vehicle Braking system● disconnecting the battery earth lead for about two minutes (does not always work however). Figure 2.7 Vehicle systems representation
  • 35. Diagnostic techniques 19division can cause as many problems as it solves. of the vehicle is determined by the output fromFor example, in which half do we put anti-lock the heater which is switched on or off in responsebrakes, mechanical or electrical. The answer is of to a signal from a temperature sensor inside thecourse both! None-the-less, it is still easier if we cabin. The feedback loop is the fact that the out-just consider one area of the vehicle and do not try put from the system, temperature, is also an inputto comprehend the whole. to the system. This is represented by Figure 2.9. Once a complex set of interacting parts such as The feedback loop in any closed loop systema motor vehicle has been ‘systemised’, the func- can be in many forms. The driver of a car with ation or performance of each part can be examined conventional heating system can form a feedbackin more detail. In other words, knowing what each loop by turning the heater down when he/she ispart of the system should do in turn helps in deter- too hot and turning it back up when cold. Themining how each part actually works. It is again feedback to a voltage regulator in an alternator isimportant to stress that the links and interactions an electrical signal using a simple wire.between various sub-systems are a very importantconsideration. Examples of this would be how thepower demands of the vehicle lighting system will 2.7.5 Block diagramshave an effect on the charging system operation, Another secret to good diagnostics is the ‘blockor in the case of a fault, how an air leak from a diagram’ approach. Most systems can be con-brake servo could cause a weak air/fuel ratio. sidered as consisting of ‘inputs to a control which To further analyse a system, whatever way it has outputs’. This technique means that complexhas been sub-divided from the whole, considera- systems can be considered in manageable ‘chunks’.tion should be given to the inputs and the out- Many complex vehicle electronic systems canputs. Many of the complex electronic systems on be represented as block diagrams. In this waya vehicle lend themselves to this form of analy- several inputs can be shown supplying informa-sis. Considering the ECU of the system as the tion to an ECU that in turn controls the systemcontrol element and looking at its inputs and out- outputs. As an example of this, consider the oper-puts is the recommended approach. ation of a vehicle alarm system (Figure 2.10). In its simplest form the inputs are the ‘sensors’ (such as door switches) and the ‘outputs’ are the actua-2.7.3 Open loop systems tors (such as the siren). The ‘control’ section isAn open loop system is designed to give the the alarm ECU.required output whenever a given input is The diagnostic approach is that if all the sen-applied. A good example of an open loop vehicle sors are providing the correct information to thesystem would be the headlights. With the given control and the actuators respond when tested,input of the switch being operated the outputrequired is that the headlights will be illuminated.This can be taken further by saying that an input Inputs Control Outputsis also required from the battery and a furtherinput of say the dip switch. The feature whichdetermines that a system is open loop is that nofeedback is required for it to operate. Figure 2.8shows this example in block diagram form. Figure 2.9 Closed loop system2.7.4 Closed loop systems DoorA closed loop system is identified by a feedback switch Warningloop. It can be described as a system where there light Voltageis a possibility of applying corrective measures if sensorthe output is not quite what is wanted. A good ECUexample of this in a vehicle is an automatic tem- Controlperature control system. The interior temperature switch Siren Movement sensor Inputs Control OutputsFigure 2.8 Open loop system Figure 2.10 Block diagram
  • 36. 20 Advanced automotive fault diagnosisthen the fault must be the control unit. If a sensor When a defective sensor is detected, the meas-does not produce the required information then ured values are replaced by a nominal value, orthe fault is equally evident. an alternative value is calculated using the infor- mation from other sensors to provide a limp- home function. With the help of an appropriate code reader or scanner, a technician can commu-2.8 On- and off-board nicate with the ECUs, read the fault memorydiagnostics and the measured values, and send signals to the actuators. Another task of self-diagnosis is to indicate a2.8.1 On-board diagnostics defect to the driver. A warning light on the dash-On-board diagnostics refers to the systems on the board is the most common method used to dovehicle carrying out some form of self-monitor- this. Regulations concerning exhaust emissionsing. The more complex automobiles become, the mean an extension of self-diagnosis is desirable.greater the number of electronic systems and the The control units will soon have to be able tomore difficult it is to register the actual condition control all exhaust gas functions and componentsin case of a defect. and to clearly indicate a defective function or Many connecting cables and adapters are the exceeding of the permissible exhaust limits.required to achieve this. Data about the different Chapter 5 covers this subject in detail.systems and their working together is needed toallow a system specific diagnosis. Modern elec-tronics with self-diagnosis supports the techni- 2.8.2 Off-board diagnosticscian by registering actual values, comparing them The continual increase in the use of electronicswith the nominal values, and diagnosing faults within vehicles represents a major challengethat are stored for repair purposes. for customer service and workshop operations. Internal to an ECU, a checksum of the program Modern diagnosis and information systems mustmemory is calculated. Then a read and write test of cope with this challenge and manufacturers ofthe random access memory (RAM) is performed. test equipment must provide instruments that areOther elements such as A/D (analogue/digital) flexible and easy to handle. Quick and reliableconverters are also checked within this test cycle. fault diagnosis in modern vehicles requires exten- During the operating time of the vehicle, the sive technical knowledge, detailed vehicle infor-ECUs are constantly checking the sensors they are mation, up-to-date testing systems and the skill toconnected to. The ECUs are then able to determine be able to apply all of these.whether a sensor has a short circuit to ground or The test equipment on the market can be sub-battery voltage, or if a cable to the sensor is open divided into two main categories:circuit. By comparing the measured values and the ● hand-held or portable instruments;stored data, an ECU is able to determine whether ● stationary equipment.the measured values exceed or are still within thetolerance required. Combining information pro- Hand-held instruments are commonly used forvided by other sensors allows the ECU to monitor the control of engine functions like ignition orfor plausibility of the sensor signals. fuel injection and the request of error codes from Measuring the current normally taken by their the ECUs.circuits is used to carry out a check on actuators. Stationary test equipment may be able to coverPowering the actuator and observing the reaction the whole range of function and performanceof the system can test the function of an actuator checks of the engine, gear, brakes, chassis, andin some cases. exhaust monitoring. Most of the common testers If discrepancies to the nominal values are diag- are used for diagnosing engine faults.nosed, the information is stored in an internal fault For repair, service, and maintenance, many dif-memory together with other parameters, such as ferent manuals and microfiches are used in work-engine temperature or speed. In this way, defects shops. It is difficult to collect all the necessarythat appear intermittent or only under certain con- information, especially when vehicles of differentditions can be diagnosed. If a fault occurs only makes have to be repaired. It is, however, becomingonce during a set period of time, it is deleted. The common to supply material on CD/DVD. Work-fault memory can be read later in the workshop and shops equipped with appropriate data systems willprovides valuable information for the technician. be able to receive updates via telephone line or by
  • 37. Diagnostic techniques 21Figure 2.11 Example fuel and ignition circuit diagramperiodic receipt of updated CDs. A committee ofthe Society of Automotive Engineers (SAE) hasprepared rules for the standardisation of manuals.2.9 Data sources2.9.1 IntroductionData is available from a number of sources; clearlythe best being direct from the manufacturer.However, for most ‘general’ repair workshopsother sources have to be found. Examples of the type of data necessary fordiagnostic and other work are as follows:● Component specification (resistance, voltage output etc.)● Diagnostics charts● Circuit diagrams (Figure 2.11)● Adjustment data● Timing belt fitting data● Component location (Figure 2.12) Figure 2.12 Component location information
  • 38. 22 Advanced automotive fault diagnosis PORSCHE Technical Data 1 2 3 4 5 1 Vehicle Identification Ref. No. 1064 2811 2810 2812 1073 2 Model 944S 944 Turbo 944 S2 928 GT 928 S4 3 4 5 Engine specially tuned for R-Cat R-Cat R-Cat R-Cat 6 Year 1986-89 1989-93 1989-93 1989-92 1989-94 7 Engine Code M44/04 M44/52 M44/41 M28/47 M28/41/42 8 No. of cylinders/Type 4/OHC 4/OHC 4/OHC 8/OHC 8/OHC 9 Capacity cm3 2479 2479 2990 4957 4957 10 Output kW (DIN hp) rpm 140 (190) 6000 184 (250) 6000 155 (211) 5800 243 (330) 6200 235 (320) 6000 11 Minimum octane rating RON 95 95 95 95 95 12 Ignition system Description Map-h Map-h Map-h Map-i Map-i 13 Trigger location Crankshaft Crankshaft Crankshaft Crankshaft Crankshaft 14 Fuel system Make Bosch Bosch Bosch Bosch Bosch 15 Type Motronic Motronic Motronic LH-Jetronic LH-Jetronic 16 Description MFI-i MFI-i MFI-i MFI-i MFI-i 17 Air metering Type Flow Flow Flow Mass Mass 18 Combined ignition and fuel ECU Yes Yes Yes No No 19 Diagnostic socket Yes Yes Yes Yes Yes 20 Tuning and emissions 2 1 21 Ignition coil supply voltage V 12.0 12.0 12.0 11.0 12.0 22 Primary resistance Ω 0.4-0.6 0.4-0.6 0.4-0.6 0.4-0.6 0.4-0.6 23 Secondary resistance Ω 5000-7200 5000-7200 5000-7200 5000-7000 5000-7200 24 Firing order 1-3-4-2 1-3-4-2 1-3-4-2 1-3-7-2-6-5-4-8 1-3-7-2-6-5-4-8 25 Ignition distributor (ECU) no. (0 261 200 080) (0 261 200 088) (0 261 200 195) (0 227 400 164) (0 227 400 034) 26 Ignition timing BTBC °Engine/rpm 10±3/840 5±3/840 10±3/840 10±2/775 10±2/675 27 alternative °Engine/rpm – – – – – 28 o without + with vacuum o – – – o 29 Ignition advance checks °Engine/rpm ECU controlled ECU controlled ECU controlled ECU controlled ECU controlled 30 a = without vacuum and basic timing °Engine/rpm – – – – – b = without vacuum with basic timing 31 c = with vacuum and basic timing °Engine/rpm – – – – – 32 Vacuum advance range °Engine – – – – – 33 Idle speed rpm 840±40 840±40 840±40 775±25 675±25 34 alternative rpm – – – – – 35 Oil temperature for CO test °C 90 90 90 90 90 36 CO content at idle - tail pipe Vol.% 1.0±0.5 0.5 Max 0.5 Max 0.5 Max 0.5 Max 37 - sample pipe Vol.% – 0.4-0.8 0.4-0.8 0.4-1.2 0.4-1.2 38 CO2/O2 content at idle speed Vol.% 13-16/0.5-2.0 14.5-16/0.1-05 14.5-16/0.1-0.5 14.5-16/0.1-0.5 14.5-16/0.1-0.5 39 HC content at idle speed ppm 300 100 100 100 100 40 Increased idle speed for CO test rpm – 2500-2800 2500-2800 2500-2800 2500-2800 41 CO content at increased idle speed Vol.% – 0.3 0.3 0.3 0.3 42 Lambda at increased idle speed λ – 0.97-1.03 0.97-1.03 0.97-1.03 0.97-10.3 43 Service checks and adjustments 44 Spark plugs Make Bosch Bosch Bosch Bosch Bosch 45 (also see Spark Plugs list) Type WR5DC WR7DC WR5DC WR7DC WR7DC 46 Electrode gap mm 0.7 0.7 0.7 0.7 0.6-0.8 47 Valve clearance - inlet mm Hydraulic Hydraulic Hydraulic Hydraulic Hydraulic 48 - exhaust mm Hydraulic Hydraulic Hydraulic Hydraulic Hydraulic 49 Compression pressure bar – – – – – 50 Oil pressure bar / rpm 3.5/6000 3.5/6000 3.5/6000 5/4000 5/5000 51 Lubricants and capacities 52 Engine oil grade SAE (API) 15W/40 (SF) 15W/40 (SF) 15W/40 (SF) 15W/40 (SF) 15W/40 (SF) 53 Engine with filter litres 6.5 7.0 7.0 7.5 7.5 54 Gearbox oil grade SAE 75W/90 75W/90 75W/90 75W/90 75W/90 55 4/5 speed litres 2.0 2.0 7.0 4.5 4.5 56 Automatic transmission fluid Type Dexron II D – – – Dexron II D 57 refill litres 6.0 – – – 7.3 58 Differential oil grade SAE 90W – – – 90W 59 front/rear litres 1.0 (AT) – – – 30 (AT) POR 3 = refer to Technical Information at end of this manufacturer ∆ = setting not adjustableFigure 2.13 Example data book example (Source: Autodata)
  • 39. Diagnostic techniques 23● Repair times This range of books and CDs (on subscrip-● Service schedules tion) is well known and well respected. Very com- prehensive manuals are available ranging from the standard ‘Data book’ to full vehicle circuit2.9.2 Autodata diagrams and engine management diagnostic testsOne of the best known and respected companies data (Figure 2.13).for supplying automotive data is Autodata, both Information about testing procedures is avail-in the UK and the USA. able as shown in Figure 2.14. These sheets includeFigure 2.14 Fuel injection testing example (Source: Autodata)
  • 40. 24 Advanced automotive fault diagnosis These engines need sophisticated test equip- ment to diagnose faults and system failures. Ineffective diagnostic work inevitably leads to vehicle problems, dissatisfied customers and labour costs which far exceed a realistic invoice value for the workshop. Clearly this is where good data comes in. The Bosch system runs from a DVD and as well as information about test procedures and test results, much more is included as well (Figure 2.15). Summary Both of the previously mentioned sources of data are excellent – and essential. It is possible toFigure 2.15 ESI[tronic] data (Source: Bosch Press) carry out diagnostic work without data, but much more difficult and less reliable. The money will be well spent.test data as well as test procedures related to spe-cific vehicles or systems.Bosch ESI[tronic]There are already over 10 million cars in the UKand over 60 million in the USA! Most of thesenow have engine management systems. Knowledge check questions To use these questions, you should first try to answer them without help but if necessary, refer back to the content of the chapter. Use notes, lists and sketches as appropriate to answer them. It is not neces- sary to write pages and pages of text! 1. List the six-stage diagnostic process in your own words. 2. Explain how the six-stage process is used by giving a simple example. 3. State the length of a standard piece of string and explain why this is relevant to diagnostics! 4. Describe how to carry out tests for an electrical short circuit. 5. Explain using a sketch, what is meant by ‘black box’ faultfinding.
  • 41. 3Tools and equipment3.1 Basic equipment the following table lists some of the basic words and descriptions relating to tools and equipment.3.1.1 IntroductionAs the complexity of the modern vehicle con- Hand tools Spanners and hammers and screwdrivers and all the other basic bits!tinues to increase, developments in suitable testequipment must follow. Many mechanical and Special tools A collective term for items not held as part of a normal tool kit. Or items required forelectronic systems now have ECUs, that contain just one specific jobself-diagnosis circuits. This is represented by Test equipment In general, this means measuring equipment.Figure 3.1. On earlier systems this was done Most tests involve measuring something andby activating the blink code output to access the comparing the result of that measurementinformation held in the ECU memory. This was to data. The devices can range from a simpledone in some cases by connecting two wires and ruler to an engine analyserthen switching on the ignition. It is now usual to Dedicated test Some equipment will only test one specificread out the fault codes on a scanner. equipment type of system. The large manufacturers Diagnostic techniques are very much linked to supply equipment dedicated to their vehicles. For example, a diagnostic devicethe use of test equipment. In other words you which plugs in to a certain type of fuelmust be able to interpret the results of tests. In injection ECUmost cases this involves comparing the result of Accuracy Careful and exact, free from mistakesa test to the reading given in a data book or other or errors and adhering closely to asource of information. By way of an introduction, standard Sensors Electronic control unit Actuators Monitoring Monitoring Computer Fault memory Prompt line Workshop tester Serial interfaceFigure 3.1 Engine control with self-diagnosis
  • 42. 26 Advanced automotive fault diagnosisCalibration Checking the accuracy of a measuring Consider measuring a length of wire with a steel instrument rule. How accurately could you measure it to theSerial port A connection to an ECU, a diagnostic tester nearest 0.5 mm? This raises a number of issues. or computer for example. Serial means the Firstly, you could make an error reading the ruler. information is passed in a ‘digital’ string like pushing black and white balls through a pipe Secondly, why do we need to know the length of in a certain order a bit of wire to the nearest 0.5 mm? Thirdly theCode reader This device reads the ‘black and white balls’ ruler may have stretched and not give the corrector scanner mentioned above, or the on-off electrical reading! signals, and converts them to language we The first and second of these issues can be dis- can understand pensed with by knowing how to read the test equip-Combined Usually now PC based, these systems can be ment correctly and also knowing the appropriatediagnostic and used to carry out tests on vehicle systems level of accuracy required. A micrometer for a pluginformation and they also contain an electronicsystem workshop manual. Test sequences guided by gap? A ruler for valve clearances? I think you get the computer can also be carried out the idea. The accuracy of the equipment itself isOscilloscope The main part of ‘scope’ is the display, which another issue. is like a TV or computer screen. A scope is Accuracy is a term meaning how close the a voltmeter but instead of readings in measured value of something is to its actual numbers it shows the voltage levels by a value. For example, if a length of about 30 cm is trace or mark on the screen. The marks on the screen can move and change very fast measured with an ordinary wooden ruler, then allowing us to see the way voltages change the error may be up to 1 mm too high or too low. This is quoted as an accuracy of Ϯ1 mm. This may also be given as a percentage which in this3.1.2 Basic hand tools case would be 0.33%.You cannot learn to use tools from a book; it is Resolution, or in other words the ‘fineness’clearly a very practical skill. However, you can with which a measurement can be made, is relatedfollow the recommendations made here and of to accuracy. If a steel ruler was made to a verycourse by the manufacturers. Even the range of high standard but only had markings of one perbasic hand tools is now quite daunting and very centimetre it would have a very low resolutionexpensive. even though the graduations were very accurate. It is worth repeating the general advice and In other words the equipment is accurate but yourinstructions for the use of hand tools. reading will not be! To ensure instruments are, and remain, accur-● Only use a tool for its intended purpose. ate there are just two simple guidelines.● Always use the correct size tool for the job you are doing. ● Look after the equipment; a micrometer thrown● Pull a wrench rather than pushing whenever on the floor will not be accurate. possible. ● Ensure that instruments are calibrated● Do not use a file or similar, without a handle. regularly – this means being checked against● Keep all tools clean and replace them in a suit- known good equipment. able box or cabinet. Here is a summary of the steps to ensure a meas-● Do not use a screwdriver as a pry bar. urement is accurate:● Always follow manufacturers’ recommenda- tions (you cannot remember everything).● Look after your tools and they will look after Step Example you! Decide on the level of Do we need to know that the accuracy required battery voltage is 12.6 V or 12.635 V?3.1.3 Accuracy of test Choose the correct A micrometer to measure theequipment instrument for the job thickness of a shim Ensure that the Most instruments will go out ofAccuracy can mean a number of slightly differ- instrument has been adjustment after a time. Youent things: looked after and should arrange for adjustment at calibrated when regular intervals. Most tool● careful and exact necessary suppliers will offer the service or● free from mistakes or errors; precise in some cases you can compare● adhering closely to a standard older equipment to new stock
  • 43. Tools and equipment 27Study the instructions Is the piston diameter 70.75 mmfor the instrument in use or 170.75 mm? Vand take the reading withcare. Ask yourself if thereading is about what you 100 k⍀ 100 k⍀expectedMake a note if you are Don’t take a chance, write it downtaking several readings 12V3.1.4 MultimetersAn essential tool for working on vehicle elec- Figure 3.2 Loading effect of a test metertrical and electronic systems is a good digitalmultimeter. Digital meters are most suitable foraccuracy of reading as well as available facilities.The following list of functions, broadly in orderfrom essential to desirable, should be considered.Function Range AccuracyDC voltage 500 V 0.3%DC current 10 A 1.0%Resistance 0 to 10 M⍀ 0.5%AC voltage 500 V 2.5%AC current 10 A 2.5%Dwell 3,4,5,6,8 cylinders 2.0%RPM 10 000 rev/min 0.2%Duty cycle % on/off 0.2% (kHz) Figure 3.3 Multimeter and accessoriesFrequency 100 kHz 0.01%Temperature Ͼ900°C 0.3% ϩ 3°CHigh current clamp 1000 A (DC) Depends on Meter resistance 1 M⍀ conditions With a parallel combined value of 1 M⍀ andPressure 3 bar 10.0% of standard 100 k⍀ ϭ 91 k⍀ the voltage drop in the circuit scale across this would be: 91/(100 ϩ 91) ϫ 12 ϭ 5.71 V A way of determining the quality of a meter, This is an error of about 5%.as well as by the facilities provided, is to con-sider the following: Meter resistance 10 M⍀● accuracy; With parallel combined value of 10 M⍀ and● loading effect of the meter; 100 k⍀ ϭ 99 k⍀ the voltage drop in the circuit● protection circuits. across this would be:The loading effect is a consideration for any form 99/(100 ϩ 99) ϫ 12 ϭ 5.97 Vof measurement. With a multimeter this relates This is an error of about 0.5%.to the internal resistance of the meter. It is rec-ommended that the internal resistance of a meter Note: This ‘invasive measurement’ error is inshould be a minimum of 10 M⍀. This not only addition to the basic accuracy of the meter.ensures greater accuracy but also prevents the Figure 3.3 shows a digital multimeter. Nowmeter from damaging sensitive circuits. that this is recognised, only two further skills are Figure 3.2 shows two equal resistors connected required – where to put the probes and what thein series across a 12 V supply. The voltage across reading you get actually means!each resistor should be 6 V. However, the internalresistance of the meter will affect the circuit con-ditions and change the voltage reading. If the 3.1.5 Logic proberesistor values were 100 k⍀ the effect of meter This device is a useful way of testing logic cir-internal resistance would be as follows. cuits but it is also useful for testing some types of
  • 44. 28 Advanced automotive fault diagnosis X plates Screen Y plates Electron beam Figure 3.5 Analogue oscilloscope principle by suitable voltages and focused into a beam. This beam is directed towards a fluorescent screen where it causes light to be given off. This is the basic cathode ray tube. The plates as shown in the figure are known as X and Y plates as they make the electron beam draw a ‘graph’ of a voltage signal. The X plates are sup- plied with a saw tooth signal, which causes the beam to move across the screen from left to right and then to ‘fly back’ and start again. Being attracted towards whichever plate has a positive potential the beam moves simply. The Y plates can now be used to show voltage variations of the signal under test. The frequency of the saw tooth signal, known as the time base, can be adjusted either automatically as is the case with many analysers or manually on a stand alone oscilloscope. The signal from the item under test can either be amplified or attenuated (reduced), much like changing the scale on a voltmeter. TheFigure 3.4 Logic probe trigger, in other words when the trace across the screen starts, can be caused internally or externally. In the case of the engine analyser triggering is often external, each time an individual spark fires or eachsensor. Figure 3.4 shows a typical logic probe. time number one spark plug fires.Most types consist of two power supply wires and A digital oscilloscope has much the same enda metal ‘probe’. The display consists of two or result as the analogue type but the signal can bethree LEDs labelled ‘high’, ‘low’ and on some thought of as being plotted rather than drawn ondevices ‘pulse’. These LEDs light up, together with the screen. The test signal is A/D converted andan audible signal in some cases, when the probe the time base is a simple timer or counter circuit.touches either a high, low or pulsing voltage. Because the signal is plotted digitally on a screenAbove or below 2.5 V is often used to determine from data in memory, the ‘picture’ can be saved,high or low on a 5 V circuit. frozen or even printed. The speed of data conver- sion and the sampling rate as well as the reso- lution of the screen are very important in ensuring3.2 Oscilloscopes accurate results. This technique is becoming the norm as including scales and notes or superim- posing two or more traces for comparison can3.2.1 Introduction enhance the display.Two types of oscilloscope are available: analogue A very useful piece of equipment becomingor digital. Figure 3.5 shows the basic operation of very popular is the PC based system as shown inan analogue oscilloscope. Heating a wire creates Figure 3.6. This is a digital oscilloscope, whicha source of electrons, which are then accelerated allows data to be displayed on a PC. The Scope
  • 45. Tools and equipment 29Figure 3.6 Multiscopecan be used for a large number of vehicle tests. All the waveforms shown in various parts ofThe waveforms used as examples in this book this book are from a correctly operating vehicle.were ‘captured’ using this device. This type of test The skill you will learn by practice is to noteequipment is highly recommended. when your own measurements vary from those shown here.3.2.2 Waveforms 3.2.3 PC based two-channelYou will find the words ‘waveform’, ‘pattern’ and‘trace’ are used in books and workshop manuals automotive oscilloscopebut they mean the same thing. When you look at (PicoScope)a waveform on a screen you must remember that Author’s Note: This section will outline the use andthe height of the scale represents voltage and the features of the PicoScope® automotive oscilloscope.width represents time. Both of these axes can I have chosen this PC based scope as a case studyhave their scales changed. They are called axes because it provides some very advanced features at abecause the ‘scope’ is drawing a graph of the volt- very reasonable price. At the time of writing (earlyage at the test points over a period of time. The 2006) the price was about £800/$1400 – very rea-time scale can vary from a few ␮s to several sonable for such a useful piece of equipment. Most (if not all) of the example waveforms in this book wereseconds. The voltage scale can vary from a few mV captured using this diagnostics kit. For more informa-to several kV. For most test measurements only tion: www.picoscope.com.two connections are needed just like a voltmeter.The time scale will operate at intervals pre-set bythe user. It is also possible to connect a ‘trigger’ The latest PicoScope two-channel PC oscillo-wire so that, for example, the time scale starts scope automotive kit is an ideal diagnostic tool.moving across the screen each time the ignition It is designed with mechanics and automotivecoil fires. This keeps the display in time with the technicians in mind, allowing fast and accuratespeed of the engine. When you use a full engine diagnosis of all the electrical and electronic com-analyser, all the necessary connections are made ponents and circuits in a modern vehicle. The kitas listed in the table in Section 3.4.1. A hand-held includes all of the components necessary to testscope has to be connected for each waveform as the engine and other systems for abnormalities.required. It is supplied with excellent automotive software
  • 46. 30 Advanced automotive fault diagnosis The two-channel PC oscilloscope in the new kit has an improved sampling rate of 20 MS/s, a 12 bit resolution, a huge buffer memory of 512 k samples and an excellent 1% level of accuracy. The automotive software is continually updated and free upgrades are available from the Pico Technology web site. The kit even comes with lifetime technical support from the Pico automo- tive specialists. The waveforms in Chapter 4 were all captured using this equipment. 3.3 Scanners/fault code readers 3.3.1 Serial port communicationsFigure 3.7 Pico Technology two-channel PC automotive A special interface of the type that is stipulatedoscilloscope by ISO 9141 is required to read data. This stand- ard is designed to work with a single or two wire port allowing many vehicle electronic systems toto collect, display, store and analyse readings. The be connected to a central diagnostic plug. Theaccessories including current clamps, ignition sequence of events to extract data from the ECUpick ups, test leads and probes, come packaged in is as listed below:a hard-wearing carry case. ● test unit transmits a code word; The powerful combination of the two-channel ● ECU responds by transmitting a baud rateoscilloscope diagnostic kit and PicoScope automo- recognition word;tive software allows thorough testing of the multi- ● test unit adopts the appropriate setting;tude of sensors and actuators in current vehicles ● ECU transmits fault codes.(Figure 3.7). The software contains a technical ref-erence library of tests and tutorials on over fifty The test unit converts these to suitable outputtopics, illustrated with waveforms. The compo- text.nents and circuits that can be tested include igni-tion, injectors, ABS, lambda oxygen sensors,relative compression, fuel pumps, CAN Bus and 3.3.2 The scanner/fault codemany others. The kit is a cost-effective ignitionand engine diagnostic tool for all automotive readertechnicians. Serial communication is an area that is continuing The two-channel automotive kit contains, to grow. A special interface is required to read data.amongst other things, the following items: This standard is designed to work with a single or two wire port, which connects vehicle electronic● PicoScope 3223 automotive oscilloscope systems to a diagnostic plug. Many functions are● 600 A AC/DC current clamp then possible when a scanner is connected. They● 60 A DC current clamp include the following.● Wide range of general leads, clips and probes for all applications ● Identification of ECU and system to ensure● Secondary ignition pickup leads that the test data is appropriate to the system● 2-pin break out lead. currently under investigation. ● Read out of current live values from sensorsThe equipment is connected to, and powered so that spurious figures can be easily recognised.through, the USB port on any modern PC or lap- Information such as engine speed, temperaturetop. This eliminates the need for a power supply air flow and so on can be displayed and checkedor batteries. against test data.
  • 47. Tools and equipment 31 Figure 3.9 AutoTap scanner and extension cableFigure 3.8 Snap-on scanner● System function stimulation allows actuators to be tested by moving them and watching for suitable response.● Programming of system changes. Basic idle CO or changes in basic timing can be programmed into the system. Figure 3.8 shows a scanner from snap-on. TAsscanner allows the technician to perform all thenecessary operations, such as fault code reading, Figure 3.10 Diagnostic connectorvia a single common connector. The portablehand-held tool has a large graphics display allow-ing clear instructions and data. Context-sensitive (CAN) plug-in-port on or under the dash (Figurehelp is available to eliminate the need to refer back 3.10). A USB connection then makes the scannerto manuals to look up fault code definitions. It connection to a computer. The AutoTap scannerhas a memory so that data can be reused even after translates the signals from the vehicle’s computer-disconnecting power from the tool. This scanner controlled sensors to easy-to-read visual displays.will even connect to a controller area network It also reads out the diagnostic trouble codes(CAN) system with a suitable adapter. (DTCs) (Figure 3.11). The software allows the technician to choose which parameters or signals they want to see and3.3.3 OBD scanner (AutoTap) whether you want to view them in tables or as Author’s Note: This section will outline the use and fea- graphs, meters or gauges (Figure 3.11). tures of the AutoTap scanner. I have chosen this par- It is possible to set the ranges and alarms ticular tool as a case study because it provides some and pick display colours. Once a screen config- very advanced features at a very competitive price. uration is created it can be saved for future use. At the time of writing (2006) the price was about £140/$200 – very reasonable for such a powerful Different screen configurations are useful for tool. The scanner is designed to work with OBD2 different vehicles, or perhaps one for major systems. However, it worked fine on all the EOBD sys- maintenance, one for tuning, one for quick checks tems I have used it on so far. For more information: at the track. www.autotap.com. Lots of data is provided in easy-to-read views with multiple parameters. Graphs can be used Like any other scan tool or code reader, the to show short-term logs, and gauges for instantAutoTap scan tool connects the special OBD2 readings.
  • 48. 32 Advanced automotive fault diagnosis Figure 3.11 Screen grab showing gauges and graphs DTCs can be checked immediately on con- the motor vehicle, it is worth remembering thatnecting the scanner and starting up the software. the machine consists basically of three parts:This gives the critical info needed in the shortest ● multimeter;time possible. When repairs are completed the ● gas analyser;tool can be used to turn off the malfunction indi- ● oscilloscope.cator light (MIL). This light is also described asthe check engine light. This is not intended to imply that other available The software will also log data, for example, tests, such as cylinder balance, are less valid, but toduring a road test. This is particularly useful for show that the analyser is not magic, it is just able todiagnosing intermittent faults. The data can be present results of electrical tests in a convenientplayed back after a road or dynamometer test. It way to allow diagnosis of faults. The key compo-can also be exported to a spreadsheet file for later nent of any engine analyser is the oscilloscopeanalysis. facility, which allows the user to ‘see’ the signal Overall, to read live data and get access to under test.powertrain (engine related) system DTCs, this is The following is a description of the facilitiesan excellent piece of equipment. available on a typical engine analyser. The new concept in garage equipment design is based on a PC, specially engineered for workshop use and enabling a flexibility of use far exceeding the3.4 Engine analysers ability of machines previously available. Software is used to give the machine its ‘per- sonality’ as an engine analyser, system tester,3.4.1 Engine analysers wheel aligner or even any of the other uses madeSome form of engine analyser became an almost of PCs. Either an infrared handset or a standardessential tool for faultfinding modern vehicle ‘qwerty’ keyboard controls the machine. Theengine systems. However, hand-held equipment is information is displayed on a super VGA moni-now tending to replace the larger analysers. The tor giving high resolution colour graphics. Outputlatest machines are now generally based around a can be sent to a standard printer when a hard copyPC. This allows more facilities that can be added is required for the customer.to by simply changing the software. Whilst engine A range of external measurement modules andanalysers are designed to work specifically with software application programmes is available.
  • 49. Tools and equipment 33The modules are connected to the host computer MOT emissions (annual UK test)by high speed RS422 or RS232 serial communi- Full MOT procedure tests are integrated and dis-cation links. Application software is loaded onto played on the screen with pass/fail diagnosis to thea hard disk. Vehicle specific data can also be department of transport specifications for both gasstored on disk to allow fast easy access to infor- analysis and diesel smoke if appropriate optionsmation but also to allow a guided test procedure. are fitted. The test results include engine rev/min The modern trend with engine analysers and oil temperature as well as the gas readings.seems to be to allow both guided test procedures These can all be printed for garage or customer use.with pass/fail recommendations for the less skilled The connections to the vehicle for standard usetechnician, and freedom to test any electrical are much the same for most equipment manu-device using the facilities available in any rea- facturers. These are listed as follows.sonable way. This is more appropriate for thehighly skilled technician. Some of the routines Connection Purpose or one example of useavailable on modern engine analysers are listedbelow. Battery positive Battery and charging voltages Battery negative A common earth connectionTune-up Coil positive To check supply voltage to coilThis is a full prompted sequence that assesses each Coil negative (adapters To look at dwell, rev/min and for DIS – distributorless primary waveformscomponent in turn with results and diagnosis dis- ignition systems)played at the end of each component test. Stored Coil HT lead clamp Secondary waveformsdata allows pass/fail diagnosis by automatically (adapters are availablecomparing results of tests with data on the disk. for DIS)Printouts can be taken to show work completed. Number one cylinder Timing light and sequence of plug lead clamp waveformsSymptom analysis Battery cable amp clamp Charging and starting currentThis allows direct access to specific tests relating Oil temperature probe Oil temperature (dip stick hole)to reported driveability problems. Vacuum connection Engine loadWaveforms Figure 3.12 shows a digital oscilloscope engineA comprehensive range of digitised waveforms analyser. This test equipment has many features ascan be displayed with colour highlights. The dis- listed previously and others such as the following.play can be frozen or recalled to look for intermit-tent faults. A standard lab scope mode is available ● High tech test screens Vacuum waveform,to allow examination of EFI (electronic fuel injec- cylinder time balance bar graph, power balancetion) or ABS traces for example. Printouts can be waveform and dual trace lab scope waveform.made from any display. An interesting feature is ● Scanner interface This allows the technician‘transient capture’ which ensures that even the to observe all related information at the samefastest spikes and intermittent signals are captured time.and displayed for detailed examination. ● Expanded memory This feature allows many screens to be saved at once, then recalledAdjustments at a later time for evaluation and reference.Selecting specific components from a menu can The tests are user controlled whereas somemake simple quick adjustments. Live readings machines have pre-programmed sequences. Someare displayed appropriate to the selection. of the screens available are as follows.Primary Secondary Diagnostic Cylinder testPrimary waveform Secondary waveform Voltage waveform Vacuum waveformPrimary parade waveform Secondary parade waveform Lab scope waveform Power balance waveformDwell bar graph kV histogram Fuel injector waveform Cylinder time balance bar graphDuty cycle/dwell bar graph kV bar graph Alternator waveform Cylinder shorting even/odd bar graphDuty cycle/voltage bar graph Burn time bar graph Cranking amps bar graph
  • 50. 34 Advanced automotive fault diagnosis Table 3.1 Reading CO% Hc (ppm) CO2% O2% Lambda (␭) AFR Before 0.6 120 14.7 0.7 1.0 14.7 catalyst After 0.2 12 15.3 0.1 1.0 14.7 catalyst measurement of CO2 and HC. At present it is not possible to measure NOx without more sophisti- cated laboratory equipment. Good four-gas emission analysers often have the following features. ● Stand alone unit not dependent on other equipment. ● Graph screen simultaneously displays up toFigure 3.12 Engine analyser four values as graphs and the graph display order is user selectable. Select from HC, CO, CO2, O2 and rev/min for graph display. ● User can create personalised letterhead for3.4.2 Exhaust gas measurement screen printouts.It has now become standard to measure four of ● Uses the non-dispersive infrared (NDIR)the main exhaust gases namely: method of detection (each individual gas absorbs infrared light at a specific rate).● carbon monoxide (CO); ● Display screens may be frozen or stored in● carbon dioxide (CO2); memory for future retrieval.● hydrocarbons (HC); ● Recalibrate at the touch of a button (if calibra-● oxygen (O2). tion gas and a regulator are used). ● Display exhaust gas concentrations in realThe emission test module is often self-contained time numerics or create live exhaust gas datawith its own display but can be linked to the main graphs in selectable ranges.analyser display. Often lambda value and the air ● Calculate and display lambda (␭) (the ideal airfuel ratio are displayed in addition to the four fuel ratio of about 14.7:1).gasses. The Greek symbol lambda (␭) is used to ● Display engine rev/min in numeric or graphrepresent the ideal air fuel ratio (AFR) of 14.7:1 form and display oil temperature along withby mass. In other words just the right amount of current time and date.air to burn up all the fuel. Typical gas, lambda ● Display engine diagnostic data from a scanner.and AFR readings are given in Table 3.1 for a ● Operate from mains supply or a 12 V battery.closed loop lambda control system, before (orwithout) and after the catalytic converter. These Accurate measurement of exhaust gas is notare for a modern engine in excellent condition only required for annual tests but is essential to(examples only – always check current data). ensure an engine is correctly tuned. Table 3.1 lists The composition of exhaust gas is now a crit- typical values measured from a typical exhaust.ical measurement and hence a certain degree of Note the toxic emissions are small, but none-accuracy is required. To this end the infrared the-less dangerous.measurement technique has become the mostsuitable for CO, CO2 and HC. Each individualgas absorbs infrared radiation at a specific rate. Oxygen is measured by electro-chemical 3.4.3 Pressure testingmeans in much the same way as the on vehicle Measuring the fuel pressure on a fuel injectionlambda sensor. CO is measured using a beam of engine is of great value when faultfinding. Manyinfrared light. A similar technique is used for the types of pressure testers are available and they
  • 51. Tools and equipment 35Figure 3.13 Pressure gauge and kit 3.4.4 Bosch KTS diagnostic equipment Author’s Note: This section will outline the use and fea- tures of the Bosch KTS 650 diagnostic system. I have chosen this particular tool as a case study because it provides everything that a technician needs to diagnose faults. The system is a combination of a scanner, mul- timeter, oscilloscope and information system (when used with Esitronic). At the time of writing (2006) the price was about £5000/$8000. For more information: www.bosch.com. Modern vehicles are being fitted with moreFigure 3.14 Compression testers and more electronics. That complicates diagnosis and repair, especially as the individual systems are often interlinked. The work of service and repairoften come as part of a kit consisting of various workshops is being fundamentally changed. Auto-adapters and connections. The principle of the motive engineers have to continually update theirgauges is that they contain a very small tube wound knowledge of vehicle electronics. But this is noin a spiral. As fuel under pressure is forced into a longer sufficient on its own. The ever-growingspiral tube it unwinds causing the needle to move number of electrical and electronic vehicle com-over a graduated scale. Figure 3.13 shows a fuel ponents is no longer manageable without modernpressure gauge as part of a kit. diagnostic technology – such as the latest range Measuring engine cylinder compression or leak- of KTS control unit diagnostic testers from Boschage is a useful test. Figure 3.14 shows an engine (Figure 3.15). In addition, more and more of thecompression tester. This device is used more to previously purely mechanical interventions oncompare cylinder compressions than to measure vehicles now require the use of electronic controlactual values. units – such as the oil change, for example.
  • 52. 36 Advanced automotive fault diagnosis Figure 3.15 Diagnostic system in use (Source: Bosch Press) Vehicle workshops operate in a very competi-tive environment and have to be able to carry outdemanding repair work efficiently, to a high stand-ard and at a competitive price on a wide range ofvehicle makes and models. The Bosch KTS con-trol-unit diagnostic testers, used in conjunctionwith the comprehensive Esitronic workshop soft-ware, offers the best possible basis for efficientdiagnosis and repair of electrical and electroniccomponents. The testers are available in differentversions, suited to the individual requirements ofthe particular workshop: The portable KTS 650with built-in computer and touch-screen can beused anywhere. It has a 20 GB hard drive, atouch-screen and a DVD drive. When being usedaway from the workshop, the power supply ofthe KTS 650 comes from the vehicle battery orfrom rechargeable batteries with one to two hours’service life. For use in the workshop, there is a Figure 3.16 Adapter and cable kit (Source: Bosch Press)tough wheeled trolley with a built-in charger unit.As well as having all the necessary adapter cables,the trolley can also carry an inkjet printer and anexternal keyboard, which can be connected to systems with electronic control systems such asthe KTS 650 via the usual PC interfaces (Figure ABS, ASR and ESP. Nowadays, the diagnostic3.16). tester may even be needed for bleeding a brake The Esitronic software package accounts for system.the in-depth diagnostic capacity of the KTS diag- In addition, KTS and Esitronic allow independ-nostic testers. With the new common rail diesel ent workshops to reset the service interval warn-systems, for example, even special functions such ing; for example, after an oil change or a routineas quantitative comparison and compression test- service, or perhaps find the correct default pos-ing can be carried out. This allows for reliable ition for the headlamps after one or both of thesediagnosis of the faulty part and avoids unneces- have been replaced.sary dismantling and re-assembly or the removal As well as ISO norms for European vehiclesand replacement of non-faulty parts. and SAE norms for American and Japanese Modern diagnostic equipment is also indispens- vehicles, the KTS testers can also deal with CANable when workshops have to deal with braking norms for checking modern CAN bus systems,
  • 53. Tools and equipment 37which are coming into use more and more fre- The multiplexer determines the connection inquently in new vehicles. The testers are con- the diagnostics socket so that communication isnected directly to the diagnostics socket via a established correctly with the selected controlserial diagnostics interface by means of an adapter unit.cable. The sequence of images shown below detail a The system automatically detects the control number of steps taken to diagnose a fault, usingunit and reads out the actual values, the error the KTS, on a vehicle that had poor runningmemory and other controller-specific data. Thanks symptoms and the MIL was illuminated.to a built-in multiplexer, it is even easier for the (My thanks to Kevin and Steve at the Boschuser to diagnose the various systems in the vehicle. training centre for their help with this section.) The first step in this procedure was to connect the equipment to the car’s diagnostic socket. The ignition should be off when the connection is made and then switched on. Connect the serial lead to the diagnostic socket On this system the data for a wide range of vehicles is included on the system. The particu- lar make and engine, etc. can be selected from the menu system. Choose the vehicle type The standard test for stored diagnostic trouble codes (DTCs) was run and the result suggested that there was a fault with the air flow sensor. The specific fault was that the signal value was too low. No real surprise as we had disconnected the sensor to simulate a fault! Take a readout from the control unit memory (DTC display)
  • 54. 38 Advanced automotive fault diagnosis This is the connection that was causing the prob- lems. Further information about its pin configura- tion can be looked up in the Esitronic database. The system also provides typical readings that should be obtained on different pins. For exam- ple, the supply and earth as well as the signal outputs. Additional tests can be carried out to deter- mine the fault. Air flow sensor connection Esitronic information for the air flow sensor The faulty connection was repaired and general checks carried out to ensure no other compo- nents had been disturbed during the testing and repair process. Make repairs The final task is to clear the fault code memory and turn off the malfunction indicator light (MIL). Road tests showed that the fault had been rectified. Erase the fault from the memory
  • 55. Tools and equipment 39Knowledge check questionsTo use these questions, you should first try to answer them without help but if necessary, refer back tothe content of the chapter. Use notes, lists and sketches to answer them. It is not necessary to writepages and pages of text!1. Explain why a good multimeter has a high internal resistance.2. List three advantages of using an oscilloscope for testing signals.3. Describe how a scanner is connected to a vehicle and what information it can provide.4. State what is meant by the term ‘accuracy’.5. List five tests carried out on a vehicle using a pressure gauge.
  • 56. 4Oscilloscope diagnostics4.1 Introduction be taken. If, under heavy braking, the ABS elec- tronic control unit (ECU) loses a signal from oneThis chapter outlines the methods used and the of the road wheels, it assumes that the wheel hasresults of using an oscilloscope to test a variety locked and releases that brake momentarily untilof systems. It will be a useful reference as all the it sees the signal return. It is therefore imperativewaveforms shown are from a correctly operating that the sensors are capable of providing a signalsystem. The chapter is split into three main sec- to the ABS ECU. If the signal produced from onetions: sensors, actuators and ignition. wheel sensor is at a lower frequency than the oth- ers the ECU may also react. Author’s Note: The waveforms in this chapter were The operation of an ABS sensor is similar captured using the PicoScope® automotive oscilloscope. to that of a crank angle sensor. A small inductive I am most grateful to the PicoTech team for supplying pick-up is affected by the movement of a toothed information and equipment to assist in the production of wheel, which moves in close proximity. The move- this chapter (www.picoscope.com). ment of the wheel next to the sensor, results in a ‘sine wave’ (Figure 4.2). The sensor, recognisable by its two electrical connections (some may have a4.2 Sensors coaxial braided outer shield), will produce an out- put that can be monitored and measured on the4.2.1 ABS speed sensor oscilloscope.waveformThe anti-lock braking system (ABS) wheel speed 4.2.2 Air flow meter – air vanesensors have become increasingly smaller andmore efficient in the course of time (Figure 4.1). waveformRecent models not only measure the speed and The vane type air flow meter is a simple poten-direction of wheel rotation but can be integrated tiometer that produces a voltage output that isinto the wheel bearing as well. proportional to the position of a vane (Figure The ABS relies upon information coming in 4.3). The vane in turn positions itself in a posi-from the sensors to determine what action should tion proportional to the amount of air flowing. The voltage output from the internal track of the air flow meter should be linear to flap move- ment; this can be measured on an oscilloscope and should look similar to the example shown in Figure 4.4. The waveform should show approximately 1.0 volt when the engine is at idle. This voltage will rise as the engine is accelerated and will pro- duce an initial peak. This peak is due to the natu- ral inertia of the air vane and drops momentarily before the voltage is seen to rise again to a peak of approximately 4.0 to 4.5 V. This voltage will however depend on how hard the engine is accel- erated, so a lower voltage is not necessarily a fault within the air flow meter. On decelerationFigure 4.1 ABS wheel speed sensors (Source: Bosch Press) the voltage will drop sharply as the wiper arm, in
  • 57. Oscilloscope diagnostics 41 Figure 4.2 ABS speed sensor waveform Figure 4.3 Vane or flap type air- flow sensor (Source: Bosch)contact with the carbon track, returns back to the clean with no ‘drop-out’ in the voltage, as this indi-idle position. This voltage may in some cases cates a lack of electrical continuity. This is com-‘dip’ below the initial voltage before returning to mon on an AFM with a dirty or faulty carbonidle voltage. A gradual drop will be seen on an track. The problem will show as a ‘flat spot’ orengine fitted with an idle speed control valve as hesitation when the vehicle is driven; this is a typ-this will slowly return the engine back to base ical problem on vehicles with high mileage thatidle as an anti-stall characteristic. have spent the majority of their working life with A time base of approximately 2 seconds plus the throttle in one position.is used. This enables the movement to be shown The ‘hash’ on the waveform is due to the vac-on one screen, from idle, through acceleration uum change from the induction pulses as the eng-and back to idle again. The waveform should be ine is running.
  • 58. 42 Advanced automotive fault diagnosis Figure 4.4 Air vane output voltage4.2.3 Air flow meter – hot wirewaveformFigure 4.5 shows a micro mechanic mass airflowsensor from Bosch. This type has been in usesince 1996. As air flows over the hot wire it coolsit down and this produces the output signal. Thesensor measures air mass because the air temper-ature is taken into account due to its cooling effecton the wire. The voltage output should be linear to airflow.This can be measured on an oscilloscope andshould look similar to Figure 4.6. The waveformshould show approximately 1.0 volt when the eng- Figure 4.5 Hot wire air mass meter (Source: Bosch Press)ine is at idle. This voltage will rise as the engineis accelerated and air volume is increased pro-ducing an initial peak. This peak is due to the ini- one screen, from idle, through acceleration andtial influx of air and drops momentarily before back to idle again. The ‘hash’ on the waveform isthe voltage is seen to rise again to another peak due to airflow changes caused by the inductionof approximately 4.0 to 4.5 V. This voltage will pulses as the engine is running.however depend on how hard the engine is accel-erated; a lower voltage is not necessarily a fault 4.2.4 Inductive crankshaft andwithin the meter. On deceleration the voltage will drop sharply camshaft sensor waveformas the throttle butterfly closes, reducing the airflow, The inductive type crank and cam sensors workand the engine returns back to idle. The final volt- in the same way. A single tooth, or toothedage will drop gradually on an engine fitted with wheel, induces a voltage into a winding in theidle speed control valve as this will slowly return sensor. The cam sensor provides engine positionthe engine back to base idle as an anti-stall char- information as well as which cylinder is onacteristic. This function normally only affects the which stroke (Figure 4.7). The crank sensor pro-engine speed from around 1200 rev/min back to vides engine speed. It also provides engine posi-the idle setting. tion in many cases by use of a ‘missing’ tooth. A time base of approximately 2 seconds plus In this particular waveform (Figure 4.8) weis used because this allows the output voltage on can evaluate the output voltage from the crank
  • 59. Oscilloscope diagnostics 43 Figure 4.6 Air mass meter waveform sensor. The voltage will differ between manufac- turers and it also increases with engine speed. The waveform will be an alternating voltage signal. The gap in the picture is due to the ‘missing tooth’ in the flywheel or reluctor and is used as a reference for the ECU to determine the engine’s position. Some systems use two reference points per revolution. The camshaft sensor is sometimes referred to as the cylinder identification (CID) sensor or a ‘phase’ sensor and is used as a reference to time sequential fuel injection.Figure 4.7 Crank sensor in position near the engine This particular type of sensor generates its ownflywheel signal and therefore does not require a voltage Figure 4.8 Crank and cam sensor output signals
  • 60. 44 Advanced automotive fault diagnosissupply to power it. It is recognisable by its two rotation (360° of camshaft rotation). The voltageelectrical connections, with the occasional addi- will be approximately 0.5 V peak to peak whiletion of a coaxial shielding wire. the engine is cranking, rising to around 2.5 V peak The voltage produced by the camshaft sensor to peak at idle as seen in the example show.will be determined by several factors, these beingthe engine’s speed, the proximity of the metalrotor to the pick-up and the strength of the mag- 4.2.5 Coolant temperaturenetic field offered by the sensor. The ECU needs sensor waveformto see the signal when the engine is started for itsreference; if absent it can alter the point at which Most coolant temperature sensors are NTC ther-the fuel is injected. The driver of the vehicle may mistors; their resistance decreases as tempera-not be aware that the vehicle has a problem if the ture increases (Figure 4.9). This can be measuredCID sensor fails, as the drivability may not be on most systems as a reducing voltage signalaffected. However, the MIL should illuminate. (Figure 4.10). The characteristics of a good inductive cam- The coolant temperature sensor (CTS) willshaft sensor waveform is a sinewave that increases usually be a two wire device with a voltage sup-in magnitude as the engine speed is increased and ply of approximately 5 V.usually provides one signal per 720° of crankshaft The resistance change will therefore alter the voltage seen at the sensor and can be monitored for any discrepancies across its operational range. By selecting a time scale of 500 seconds and con- necting the oscilloscope to the sensor, the output voltage can be monitored. Start the engine and in the majority of cases the voltage will start in the region of 3 to 4 V and fall gradually. The voltage will depend on the temperature of the engine. The rate of voltage change is usually linear with no sudden changes to the voltage, if the sen- sor displays a fault at a certain temperature, it will show up in this test. 4.2.6 Hall effect distributor pick-up waveform Hall sensors are now used in a number of ways.Figure 4.9 Temperature sensor The ignition distributor is very common but they Figure 4.10 Decreasing voltage from the temperature sensor
  • 61. Oscilloscope diagnostics 45are also used by ABS for monitoring wheel speed 4.2.7 Inductive distributorand as transmission speed sensors, for example pick-up waveform(Figure 4.11). This form of trigger device is a simple digital This particular type of pick-up generates its own‘on/off switch’ which produces a square wave out- signal and therefore does not require a voltageput that is recognised and processed by the igni- supply to power it. The pick-up is used as a sig-tion control module or engine management ECU. nal to trigger the ignition amplifier or an ECU. The trigger has a rotating metal disc with open- The sensor normally has two connections. If aings that pass between an electromagnet and the third connection is used it is normally a screen tosemiconductor (Hall chip). This action produces reduce interference.a square wave that is used by the ECU or ampli- As a metal rotor spins, a magnetic field is alt-fier (Figure 4.12). ered which induces an ac voltage from the pick- The sensor will usually have three connections up. This type of pick-up could be described as awhich are: (1) a stabilised supply voltage, (2) an small alternator because the output voltage risesearth and (3) the output signal. The square wave as the metal rotor approaches the winding, sharplywhen monitored on an oscilloscope may vary in dropping through zero volts as the two compo-amplitude; this is not usually a problem as it is nents are aligned and producing a voltage in thethe frequency that is important, not the height of opposite direction as the rotor passes. The wave-the voltage. However, in most cases the amplitude/ form is similar to a sine wave (Figure 4.13); how-voltage will remain constant. ever, the design of the components are such that a more rapid switching is evident. The voltage produced by the pick-up will be determined by three main factors: ● Engine speed – the voltage produced will rise from as low as 2 to 3 V when cranking, to over 50 V, at higher engine speeds ● The proximity of the metal rotor to the pick- up winding – an average air gap will be in the order of 0.2 to 0.6 mm (8 to 14 thou), a larger air gap will reduce the strength of the mag- netic field seen by the winding and the output voltage will be reduced ● The strength of the magnetic field offered by the magnet – the strength of this magnetic field determines the effect it has as it ‘cuts’Figure 4.11 Distributors usually contain a Hall effect or induc- through the windings and the output voltagetive pulse generator (Source: Bosch press) will be reduced accordingly. Figure 4.12 Hall output waveform
  • 62. 46 Advanced automotive fault diagnosis Figure 4.13 Inductive pick-up output signal an appropriate time scale must be set – in the case of the example waveform 0–500 ms and a 0–5 volt scale. The best way to test a knock sensor is to remove the knock sensor from the engine and to tap it with a small spanner; the resultant wave- form should be similar to the example shown. Note: When refitting the sensor tighten to the correct torque setting as over tightening can damage the sensor and/or cause it to produce incorrect signals.Figure 4.14 Knock sensor 4.2.9 Oxygen sensor (Titania) waveformA difference between the positive and the nega-tive voltages may also be apparent as the negative The lambda sensor, also referred to as the oxygenside of the sine wave is sometimes attenuated sensor, plays a very important role in the control(reduced) when connected to the amplifier circuit, of exhaust emissions on a catalyst equipped vehi-but will produce perfect ac when disconnected and cle (Figure 4.16).tested under cranking conditions. The main lambda sensor is fitted into the exhaust pipe before the catalytic converter. The sensor will have four electrical connections. It4.2.8 Knock sensor waveform reacts to the oxygen content in the exhaust systemThe optimal point at which the spark ignites the and will produce an oscillating voltage betweenair/fuel mixture is just before knocking occurs. 0.5 V (lean) to 4.0 V, or above (rich) when runningHowever, if the timing is set to this value, under correctly. A second sensor to monitor the catalystcertain conditions knock (detonation) will occur. performance may be fitted downstream of theThis can cause serious engine damage as well as converter.increasing emissions and reducing efficiency. Titania sensors, unlike Zirconia sensors, require A knock sensor is used by some engine man- a voltage supply as they do not generate their ownagement systems (Figure 4.14). The sensor is voltage. A vehicle equipped with a lambda sensora small piezo-electrical crystal that, when cou- is said to have ‘closed loop’, this means that afterpled with the ECU, can identify when knock the fuel has been burnt during the combustionoccurs and retard the ignition timing accordingly process, the sensor will analyse the emissions and(Figure 4.15). adjust the engine’s fuelling accordingly. The frequency of knocking is approximately Titania sensors have a heater element to assist15 kHz. As the response of the sensor is very fast the sensor reaching its optimum operating
  • 63. Oscilloscope diagnostics 47 Figure 4.15 Knock sensor output signal will produce a small voltage depending on the Air/ Fuel mixture seen at the time. The voltage range seen will, in most cases, vary between 0.2 and 0.8 V. The 0.2 V indicates a lean mixture and a voltage of 0.8 V shows a richer mixture. A vehicle equipped with a lambda sensor is said to have ‘closed loop’, this means that after the fuel has been burnt during the combustion process, the sensor will analyse the emissions and adjust the engine’s fuelling accordingly. Lambda sensors can have a heater element to assist the sensor reaching its optimum operatingFigure 4.16 Titania knock sensor in position temperature. Zirconia sensors when working cor- rectly will switch approximately once per second (1 Hz) and will only start to switch when at normaltemperature. The sensor when working correctly operating temperature. This switching can be seenwill switch approximately once per second (1 Hz) on the oscilloscope, and the waveform should lookbut will only start to switch when at normal oper- similar to the one in the example waveform ofating temperature. This switching can be seen on Figure 4.19.the oscilloscope, and the waveform should looksimilar to the one in Figure 4.17. 4.2.11 Throttle position potentiometer waveform4.2.10 Oxygen sensor (Zirconia) This sensor or potentiometer is able to indicate towaveform the ECU the exact amount of throttle opening dueThe lambda sensor is also referred to as the oxygen to its linear output (Figure 4.20).sensor or a heated exhaust gas oxygen (HEGO) The majority of modern management systemssensor and plays a very important role in control of use this type of sensor. It is located on the throt-exhaust emissions on a catalytic equipped vehicle. tle butterfly spindle. The ‘throttle pot’ is a three-The lambda sensor is fitted into the exhaust pipe wire device having a 5 V supply (usually), an earthbefore the catalytic converter (Figure 4.18). A sec- connection and a variable output from the centreond sensor to monitor the catalyst performance pin. As the output is critical to the vehicle’s per-may be fitted downstream of the converter. formance, any ‘blind spots’ within the internal The sensor will have varying electrical con- carbon track’s swept area, will cause ‘flat spots’nections and may have up to four wires; it reacts and ‘hesitations’. This lack of continuity can beto the oxygen content in the exhaust system and seen on an oscilloscope.
  • 64. 48 Advanced automotive fault diagnosis A good throttle potentiometer should show a voltages will be manufacturer specific, many aresmall voltage at the throttle closed position, grad- non-adjustable and the voltage will be in the regionually rising in voltage as the throttle is opened and of 0.5 to 1.0 V at idle rising to 4.0 V (or more) withreturning back to its initial voltage as the throttle a fully opened throttle. For the full operationalis closed. Although many throttle position sensor range, a time scale around 2 seconds is used. Figure 4.17 Titania lambda sensor output Figure 4.18 Zirconia type oxygen sensor Figure 4.19 Zirconia oxygen sensor output
  • 65. Oscilloscope diagnostics 49 Figure 4.20 Throttle pot output voltage4.2.12 Road speed sensor As the road speed is increased the frequency(Hall effect) of the switching should be seen to increase. This change can also be measured on a multimeterTo measure the output of this sensor, jack up the with frequency capabilities. The sensor will bedriven wheels of the vehicle and place on axle located on either the speedometer drive outputstands on firm level ground. Run the engine in from the gearbox or to the rear of the speedome-gear and then probe each of the three connections ter head if a speedo cable is used. The signal is(ϩ, Ϫ and signal). used by the engine ECU and if appropriate, the transmission ECU. Figure 4.21 Hall effect road speed sensor waveform4.3 Actuators by multi-pulsing of the injector in the remainder of the trace (Figure 4.23). This ‘current limiting’ section of the waveform is called the supplemen-4.3.1 Single point injector tary duration and is the part of the injection tracewaveform that expands to increase fuel quantity.Single point injection is also sometimes referredto as throttle body injection (Figure 4.22). A single injector is used (on larger engines 4.3.2 Multi-point injectortwo injectors can be used) in what may have theoutward appearance to be a carburettor housing. waveform The resultant waveform from the single point The injector is an electromechanical devicesystem shows an initial injection period followed which is fed by a 12 volt supply (Figure 4.24).
  • 66. 50 Advanced automotive fault diagnosis Figure 4.22 Throttle body with a single injector Figure 4.23 Single point injector waveform Figure 4.24 Multi-point injectors on the railThe voltage will only be present when the engine feature built into the relay; most modern systemsis cranking or running because it is controlled by control the relay from the ECU.a relay that operates only when a speed signal is The length of time the injector is held open willavailable from the engine. Early systems had this depend on the input signals seen by the ECU from
  • 67. Oscilloscope diagnostics 51 Figure 4.25 Multi-point injector waveformits various engine sensors. The held open time or Monitoring the injector waveform using both volt-‘injector duration’ will vary to compensate for cold age and amperage, allows display of the ‘correct’engine starting and warm-up periods. The duration time that the injector is physically open. The cur-time will also expand under acceleration. The rent waveform (the one starting on the zero line)injector will have a constant voltage supply while shows that the waveform is ‘split’ into two defi-the engine is running and the earth path will be ned areas.switched via the ECU, the result can be seen in the The first part of the current waveform is respon-example waveform (Figure 4.25). When the earth sible for the electromagnetic force lifting the pin-is removed a voltage is induced into the injector tle; in Figure 4.26 the time taken is approximatelyand a spike approaching 60 V is recorded. 1.5 ms; this is often referred to as the solenoid The height of the spike will vary from vehicle reaction time. The remaining 2 ms is the actualto vehicle. If the value is approximately 35 V, it time the injector is fully open. This, when takenis because a zener diode is used in the ECU to as a comparison against the injector voltage dura-clamp the voltage. Make sure the top of the spike tion, is different to the 3.5 ms shown. The secretis squared off, indicating the zener dumped the is to make sure you compare like with like!remainder of the spike. If it is not squared, thatindicates the spike is not strong enough to makethe zener fully dump, meaning there is a problem 4.3.3 Bosch common rail dieselwith a weak injector winding. If a zener diode isnot used in the computer, the spike from a good injector waveforminjector will be 60 V or more. Common rail diesel systems are becoming more Multi-point injection may be either sequential common (Figure 4.27)!or simultaneous. A simultaneous system will fire It can be clearly seen from the example wave-all four injectors at the same time with each cylin- form (Figure 4.28) that there are two distinctiveder receiving two injection pulses per cycle (720° points of injection, the first being the ‘pre-crankshaft rotation). A sequential system will injection’ phase, with the second pulse being thereceive just one injection pulse per cycle, this is ‘main’ injection phase.timed to coincide with the opening of the inlet As the throttle is opened, and the engine isvalve. accelerated, the ‘main’ injection pulse expands As a very rough guide the injector durations in a similar way to a petrol injector. As the throt-for an engine at normal operating temperature, at tle is released, the ‘main’ injection pulse disap-idle speed are: pears until such time as the engine returns to just above idle.● 2.5 ms – simultaneous Under certain engine conditions a third phase● 3.5 ms – sequential. may be seen, this is called the ‘post injection’
  • 68. 52 Advanced automotive fault diagnosis Figure 4.26 Injector voltage and current measurements Figure 4.27 Common rail diesel pump, rail, injectors and ECU (Source: Bosch Press) Figure 4.28 CR injector (current) waveform showing pre and main injection pulses
  • 69. Oscilloscope diagnostics 53phase and is predominantly concerned with con- ance the two air paths. The position of the valvetrolling the exhaust emissions. tends to take up an average position determined by the supplied signal. As the example waveform in Figure 4.30 shows,4.3.4 Electromagnetic idle speed the earth path is switched and the resultant pic-control valve waveform ture is produced. Probing onto the supply side willThis device contains a winding, plunger and spring produce a straight line at system voltage. When(Figure 4.29). When energised the port opens and the earth circuit is monitored a ‘saw tooth’ wave-when not it closes. form will be seen. The electromagnetic idle speed control valve(ISCV) will have two electrical connections; usu- 4.3.5 Rotary idle speed controlally a voltage supply at battery voltage and a swit-ched earth. valve waveform The rate at which the device is switched is The rotary idle speed control valve (ISCV) willdetermined by the ECU to maintain a prerequisite have two or three electrical connections, with aspeed according to its programming. The valve voltage supply at battery voltage and either a sin-will form an air bypass around the throttle butter- gle or a double switched earth path (Figure 4.31).fly. If the engine has an adjustable air by-pass and The device is like a motor that only ever rotatesan ISCV, it may require a specific routine to bal- about half a turn in each direction!Figure 4.29 Electromagnetic idle speed control valve Figure 4.31 Rotary idle speed control valve Figure 4.30 Signal produced by an electromagnetic idle speed control valve
  • 70. 54 Advanced automotive fault diagnosis The rate at which the earth path is switched is earthed to ground. These devices may also be useddetermined by the ECU to maintain a prerequi- to control the position of control flaps, for example,site idle speed according to its programming. as part of a heating and ventilation system. The valve will form an air bypass past the throt- The individual earth paths can be checkedtle butterfly, to form a controlled air bleed within using the oscilloscope. The waveforms should bethe induction tract. The rotary valve will have similar on each path. Variations to the examplethe choice of either single or twin earth paths, the shown in Figure 4.34 may be seen between dif-single being pulled one way electrically and ferent systems.returned to its closed position via a spring; thedouble switched earth system will switch thevalve in both directions. This can be monitored 4.4 Ignition systemon a dual trace oscilloscope. As the examplewaveform in Figure 4.32 shows, the earth path is 4.4.1 Ignition primaryswitched and the resultant picture is produced. waveformThe idle control device takes up a position deter- The ignition primary waveform is a measure-mined by the on/off ratio (duty cycle) of the sup- ment of the voltage on the negative side of theplied signal. ignition coil. The earth path of the coil can pro- Probing onto the supply side will produce a duce over 350 V. Different types of ignition coilsstraight line at system voltage and when the earthcircuit is monitored a square wave will be seen.The frequency can also be measured as can theon/off ratio.4.3.6 Stepper motor waveformThe stepper or stepper motor is a small electro-mechanical device that allows either an air by-pass circuit or a throttle opening to alter in positiondepending on the amounts that the stepper isindexed (moved in known steps) (Figure 4.33). Stepper motors are used to control the idle speedwhen an idle speed control valve is not employed.The stepper may control an ‘air bypass’ circuit byhaving four or five connections back to the ECU.The earths enable the control unit to move the Figure 4.33 Stepper motor and throttle potentiometer on amotor in a series of ‘steps’ as the contacts are throttle body Figure 4.32 Signal supplied to a rotary idle control valve
  • 71. Oscilloscope diagnostics 55 Figure 4.34 Stepper motor signals amplifier stops increasing the primary current and it is maintained until the earth is removed from the coil. This is the precise moment of ignition. The vertical line at the centre of the trace is in excess of 200 V, this is called the ‘induced volt- age’. The induced voltage is produced by magnetic inductance. At the point of ignition, the coil’s earth circuit is removed and the magnetic flux collapses across the coil’s windings. This induces a voltage between 150 and 350 V. The coil’s high tension output will be proportional to this induced volt- age. The height of the induced voltage is some- times referred to as the primary peak volts.Figure 4.35 Direct ignition coils in position From the example current waveform (in Figure 4.37), the limiting circuit can be seen in operation. The current switches on as the dwell period startsproduce slightly different traces but the funda- and rises until the required value is achieved (usu-mental parts of the trace and principles are the ally about 8A). At this point the current is main-same (Figure 4.35). tained until it is released at the point of ignition. In the waveform shown in Figure 4.36, the hor- The dwell will expand as the engine revs areizontal voltage line at the centre of the oscilloscope increased to maintain a constant coil saturationis at fairly constant voltage of approximately 40 V, time. This gives rise to the term ‘constant energy’.which then drops sharply into what is referred to The coil saturation time can be measured and thisas the coil oscillation. The length of the horizontal will remain the same regardless of engine speed.voltage line is the ‘spark duration’ or ‘burn time’, Figure 4.37 shows a charge time of about 3.5 ms.which in this particular case is about 1 ms. Thecoil oscillation period should display a minimumof four to five peaks (both upper and lower). A loss 4.4.2 Ignition secondaryof peaks would indicate a coil problem. There is no current in the coil’s primary circuit waveformuntil the dwell period. This starts when the coil is The ignition secondary waveform is a measure-earthed and the voltage drops to zero. The dwell ment of the HT output voltage from the ignitionperiod is controlled by the ignition amplifier or coil. Some coils can produce over 50,000 V. Dif-ECU and the length of the dwell is determined by ferent types of ignition coils produce slightly dif-the time it takes to build up to about 8A. When ferent traces but the fundamental parts of thethis predetermined current has been reached, the trace and principles are the same (Figure 4.38).
  • 72. 56 Advanced automotive fault diagnosis Figure 4.36 Primary ignition voltage trace Figure 4.37 Primary ignition current trace The ignition secondary picture shown in Figure4.39 waveform is from an engine fitted with elec-tronic ignition. In this case, the waveform has beentaken from the main coil lead (king lead). Suitableconnection methods mean that similar traces canbe seen for other types of ignition system. The secondary waveform shows the length oftime that the HT is flowing across the spark plugelectrode after its initial voltage, which is requiredto initially jump the plug gap. This time is referredto as either the ‘burn time’ or the ‘spark duration’.In the trace shown it can be seen that the hori-zontal voltage line in the centre of the oscilloscopeis at fairly constant voltage of approximately 3 or Figure 4.38 Spark plugs (Source: Bosch Press)4 kV, which then drops sharply into the ‘coil oscil-lation’ period. be faulty. The period between the coil oscillation The coil oscillation period should display a and the next ‘drop down’ is when the coil is at restminimum of four or five peaks (both upper and and there is no voltage in the secondary circuit.lower). A loss of peaks indicates that the coil may The ‘drop down’ is referred to as the ‘polarity
  • 73. Oscilloscope diagnostics 57peak’, and produces a small oscillation in the fluctuating and the display will be seen to moveopposite direction to the plug firing voltage. This up and down. The maximum voltage at the sparkis due to the initial switching on of the coil’s pri- plug, can be seen as the ‘Ch A: Maximum (kV)’mary current. reading at the bottom of the screen. The plug firing voltage is the voltage required It is a useful test to snap the throttle and observeto jump and bridge the gap at the plug’s electrode, the voltage requirements when the engine is undercommonly known as the ‘plug kV’. In this exam- load. This is the only time that the plugs are placedple the plug firing voltage is about 12 or 13 kV. under any strain and is a fair assessment of how When the plug kVs are recorded on a DIS or they will perform on the road.coil per cylinder ignition system, the voltage seen The second part of the waveform after the ver-on the waveform (Figure 4.40) should be in the tical line is known as the spark line voltage. This‘upright position’. If the trace is inverted it would second voltage is the voltage required to keep thesuggest that either the wrong polarity has been plug running after its initial spark to jump the gap.selected from the menu or in the case of DIS, the This voltage will be proportional to the resistanceinappropriate lead has been chosen. The plug volt- within the secondary circuit. The length of the lineage, while the engine is running, is continuously can be seen to run for approximately 2 ms. Figure 4.39 Ignition secondary trace Figure 4.40 Distributorless ignition
  • 74. 58 Advanced automotive fault diagnosis4.5 Other components If the alternator is suffering from a diode fault, long downward ‘tails’ appear from the trace at reg- ular intervals and 33% of the total current output4.5.1 Alternator waveform will be lost. A fault within one of the three phasesChecking the ripple voltage produced by an alter- will show a similar picture to the one illustratednator is a very good way of assessing its condi- but is three or four times the height, with the basetion (Figure 4.41). to peak voltage in excess of 1 V. The example waveform shown in Figure 4.42 The voltage scale at the side of the oscillo-illustrates the rectified output from the alternator. scope is not representative of the charging volt-The output shown is correct and that there is no age, but is used to show the upper and lowerfault within the phase windings or the diodes (rec- limits of the ripple. The ‘amplitude’ (voltage/tifier pack). height) of the waveform will vary under different The three phases from the alternator have conditions. A fully charged battery will show abeen rectified to dc from its original ac and the ‘flatter’ picture, while a discharged battery willwaveform shows that the three phases are all show an exaggerated amplitude until the batteryfunctioning. is charged. Variations in the average voltage of Figure 4.41 Alternator Figure 4.42 Alternator ripple voltage
  • 75. Oscilloscope diagnostics 59the waveform are due to the action of the voltage battery is charged, and the starter and associatedregulator. circuit are in good condition. The current for a typical 4 cylinder petrol/gaso- line engine is in the region of 100 to 200 A.4.5.2 Relative compression In the waveform shown, the initial peak of cur-petrol waveform rent (approximately 400 A) is the current requiredMeasuring the current drawn by the starter motor to overcome the initial friction and inertia to(Figure 4.43) is useful to determine starter condi- rotate the engine. Once the engine is rotating, thetion but it is also useful as an indicator of engine current will drop. It is also worth mentioning thecondition. small step before the initial peak, which is being The purpose of this particular waveform caused by the switching of the starter solenoid.(Figure 4.44) is therefore to measure the current The compressions can be compared againstrequired to crank the engine and to evaluate the each other by monitoring the current required torelative compressions. push each cylinder up on its compression stroke. The amperage required to crank the engine The better the compression the higher the currentdepends on many factors, such as: the capacity of demand and vice versa. It is therefore importantthe engine, the number of cylinders, the viscosity that the current draw on each cylinder is equal.of the oil, the condition of the starter motor, thecondition of the starter’s wiring circuit and 4.5.3 CAN-H and CAN-Lthe compressions in the cylinders. To evaluate waveformthe compressions therefore, it is essential that the Controller area network (CAN) is a protocol used to send information around a vehicle on data bus. It is made up of voltage pulses that rep- resent ones and zeros, in other words, binary sig- nals. The data is applied to two wires known as CAN-high and CAN-low (Figure 4.45). In this display, it is possible to verify that data is being continuously exchanged along the CAN bus. It is also possible to check that the peak to peak voltage levels are correct and that a signal is present on both CAN lines. CAN uses a differen- tial signal, and the signal on one line should be a coincident mirror image (the signals should line up) of the data on the other line (Figure 4.46). The usual reason for examining the CAN sig-Figure 4.43 Starter and ring gear nals is where a CAN fault has been indicated by Figure 4.44 Spark ignition engine cranking amps
  • 76. 60 Advanced automotive fault diagnosisOBD, or to check the CAN connection to a sus- be viewed. This enables the mirror image naturepected faulty CAN node. The vehicle manufac- of the signals, and the coincidence of the edgesturers’ manual should be referred to for precise to be verified.waveform parameters. The signal shown is captured on a fast time-base and allows the individual state changes to 4.6 Summary ‘Scope’ diagnostics is now an essential skill for the technician to develop. As with all diagnostic techniques that use test equipment, it is necessary for the user to know how: ● the vehicle system operates; ● to connect the equipment; ● readings should be interpreted. Remember that an oscilloscope is really just a voltmeter or ammeter but that it draws a picture of the readings over a set period of time. Learn what good waveforms look like, and then you willFigure 4.45 OBD socket – pin 6 is CAN-high and pin 14 is be able to make good judgements about what isCAN-low wrong when they are not so good! Figure 4.46 CAN-high and low signals on a dual trace scope Knowledge check questions To use these questions, you should first try to answer them without help but if necessary, refer back to the content of the chapter. Use notes, lists and sketches to answer them. It is not necessary to write pages and pages of text! 1. Explain the terms ‘timebase’, ‘amplitude’ and ‘voltage scale’. 2. Make a sketch of ignition primary and secondary waveforms. Label each part and state which aspects indicate that no faults are present. 3. Describe how to connect an oscilloscope to examine the signal supplied to a single point (throttle body) injector. 4. State the typical output voltage (peak to peak) of an inductive crankshaft sensor at cranking, idle and 3000 rev/min. Sketch the waveform to show the aspects that indicate engine speed and engine position. 5. Explain with the aid of a sketch, why current limiting is used on the primary circuit of an ignition system.
  • 77. 5On-board diagnostics5.1 On-board diagnostics – over a total of 24 billion miles (Figure 5.1). Already, smog was apparent and people suffereda first perspective with stinging eyes, sore throats and breathing diffi- Authors Note: I am most grateful to Alan Malby culties. Local Government initiated a study into the (Ford Motor Company) for his excellent contribution cause of the problem, and scientists at CALTEC to this chapter. and the University of California investigated the problem of smog (Figure 5.2). In 1945, after the conclusion of the war, Los5.1.1 Introduction Angeles began its air pollution control programOriginating in the USA, and subsequently fol- and established the Bureau of Smoke Control. Onlowed by Europe, Asia and many others, govern- June 10, 1947 the then California Governor, Earlments around the globe have augmented vehicle Warren, signed the Air Pollution Control Act. Byemissions control legislation. This includes arequirement that all vehicles sold within theirterritories must support an on-board diagnosticsystem that can be operated to determine the serv-iceability of the vehicle’s emission control sys-tems, sub-systems and components. Enabled by the increasing advances in elec-tronics and microprocessor software development,this system, now commonly termed as on-boarddiagnostics (OBD), has been developed overrecent years and is now implemented by all majormotor vehicle manufacturers. Furthermore, thishas been extended to allow diagnosis of none-emission related vehicle systems. Later in this chapter, and in the final chapterof the book, there is more information aboutthe development of on-board diagnostics and thepotential for further improvements. Some aspectsare repeated for reasons of clarity. Figure 5.1 Early traffic jam!5.1.2 Vehicle emissions andenvironmental healthFrom as early as 1930, the subject of vehicle engineemissions influencing environmental health wasvery topical in the State of California. Already witha population of 2 million vehicles, scores of peoplehave died and thousands have become sick due toair pollution related illnesses. Following the outbreak of WW2, the popula-tion of California had risen to some 7 millionpeople in 1943, with 2.8 million vehicles travelling Figure 5.2 Smog over Los Angeles
  • 78. 62 Advanced automotive fault diagnosis1950, California’s population had reached 11 mil- emissions standards for hydrocarbons (HC) andlion people. Total registered vehicles in California carbon monoxide (CO) and the California High-exceeded 4.5 million and Vehicle Miles Travelled way Patrol began random roadside inspections of(VMT) was 44.5 billion. The search for the root the smog control devices fitted to vehicles.cause of smog production went on. Reports of The following year the Governor of California,deaths in other countries became apparent. For Ronald Reagan, signed the Mulford-Carrell Airexample, in the early 1950s, thousands of people Resources Act. This effectively allowed the state ofdied in London of a ‘mystery fog’. California to set its own emissions standards. The In 1952, Dr. Arie Haagen-Smit determined the same year saw the formation of the California Airroot cause of smog production. He surmised that Resources Board (CARB), which was created fromengine pollutants, Carbon Monoxide (CO), Hydro- the amalgamation of the Motor Vehicle Pollutioncarbons (HC) and various Oxides of Nitrogen or Control Board and the Bureau of Air Sanitation.‘NOx’ combine to generate the smog, which con- In 1969 the first California State Ambient Airsists of Ozone and Carbon Dioxide. Quality Standards were extended by California Carbon Dioxide is a pollutant, which is now for photochemical oxidants, suspended particu-said to contribute to global warming and climate lates, sulphur dioxide (SO2), nitrogen dioxidechange. Ozone, occupying a region of the lower (NO2), and carbon monoxide (CO). California’satmosphere, is now known to cause respiratory ill population reached 20 million people. Total reg-health, lung disease and is also thought to make a istered vehicles exceeded 12 million and VMT ismuch greater contribution to the green house effect 110 billion.than even Carbon Dioxide. Total cumulative California vehicle emissions The State became a centre for environmental for HC and NOx are estimated at 1.6 million tonsactivism. Naturally, amidst a public outcry to pre- per year. In 1970, the US Environmental Protectionserve the local environment, the State began to leg- Agency (EPA) was created; its primary directiveislate for controls on motor vehicle emissions. So was, and still is, to protect all aspects of the envir-began an initiative that would span over 50 years, onment. The next seven years witnessed furtherone that would drive change in a world industry development of emissions control legislation andand lead the world in the fight for clean air. increasing employment of vehicle emissions con- trol technology. In 1971 CARB adopted the first vehicle NOx5.1.3 History of the emissions standards. The EPA announced National Ambient Air Quality Standards for particulates, hydrocar-control legislation bons (HC), carbon monoxide (CO), nitrogen diox-In 1960, The Motor Vehicle Pollution Control ide (NO2), photochemical oxidants (includingBoard was established with a mandate to certify ozone) and sulphur dioxide (SO2).devices proposed to be fitted on cars for sale The first Two-Way Catalytic Converters camein California. In addition, The Federal Motor into use in 1975 as part of CARB’s Motor Vehi-Vehicle Act of 1960 was enacted, requiring cle Emission Control Program followed by anFederal research to combat motor vehicle engine announcement that CARB will limit lead inpollution. Manufacturers made technology gasoline.improvements and during this period, California’spopulation reached 16 million people. Total regis- Table A California State-wide emissions 1969tered vehicles approached 8 million and VehicleMiles Travelled (VMT) was 71 billion. State-wide average emissions (per vehicle) In 1961, in an effort to control hydrocarbon NOx (g/mile) HC (g/mile)crankcase emissions, the first piece of vehicleemissions control legislation mandating the use of 5.3 8.6specific hardware was issued. Positive CrankcaseVentilation (PCV) controls hydrocarbon crank- Table B California State-wide emissions 1980case emissions by extracting gases from the crank-case and re-circulating them back into the fresh State-wide average emissions (per vehicle)air/fuel charge in the cylinders. A key turning point in history, in 1966 the NOx (g/mile) HC (g/mile)California Motor Vehicle Pollution Control Board 4.8 5.5pioneered the adoption of vehicle tailpipe
  • 79. On-board diagnostics 63 In 1977, Volvo introduced a vehicle marketed negative torque conditions (overrun or cruiseas ‘Smog-Free’. This vehicle supported the first down), to name but a few.Three-Way Catalytic (TWC) Converter to control This development continued and expandedhydrocarbon (HC), nitrogen oxides (NOx), and meaning that these systems demanded an ever-carbon monoxide (CO) emissions. increasing array of sensors and actuators. The reso- In 1980, the California population reached 24 lution of measurement, control of air/fuel ratio,million people. Total registered vehicles were in actuator displacement rates and accuracy of dis-the region of 17 million and VMT was 155 billion. placement, etc. was way beyond that which could Total cumulative California vehicle emissions be provided by traditional existing mechanicalfor NOx and HCs remain at 1970 levels of 1.6 mil- technologies.lion tons/year despite a rise of 45 billion in VMT At about this time, an enabler was providedover those ten years. in the form of recent advances in microprocessor The legislative controls had clearly begun to technology. The path was clear, the drivers forhave a positive effect. Spurred on by this victory, on-board diagnostic system monitoring were inCARB began a program of compliance testing on force and the enablers were available.‘in use’ vehicles in order to determine whether On-board diagnostics was born.they continue to comply with emission standardsas vehicle mileage increases. Vehicle manufac-turers commissioned the development of moredurable emission control systems. 5.2 What is on-board 1984 saw the introduction of the biennial diagnostics?California Smog Check Program, the aim of whichwas to identify vehicles in need of maintenance Fundamentally, a contemporary microprocessorand to confirm the effectiveness of their emissions based on-board diagnostics or OBD system iscontrol systems. intended to self diagnose and report when the per- The mid-term period of emissions control legis- formance of the vehicle’s emissions control sys-lation ended in 1988 with a key announcement, tems or components have degraded. This is to thewhich saw the beginning of on-board diagnostics. extent that the tailpipe emissions have exceededThe California Clean Air Act was signed and legislated levels or are likely to be exceeded in theCARB adopted regulations that required that all long term.1994 and beyond model year cars were fitted with When an issue occurs the OBD system illumin-‘On-board Diagnostic’ systems. The task of these ates a warning lamp known as the malfunctionsystems was, as it is now: indicator lamp (MIL) or Malfunction Indicator (MI) on the instrument cluster. In the United To monitor the vehicle emissions control systems States this symbol often appears with the phrase performance and alert owners when here is a ‘Check Engine’, ‘Check’ or ‘Service Engine Soon’ malfunction that results in the lack of function contained within it (Figure 5.3). European vehicles of an emissions control system/sub-system or component.5.1.4 Introduction of vehicleemissions control strategiesTo meet the ever increasing but justifiable and‘wanted’ need of vehicle emissions control legisla-tion, vehicle manufacturers were forced to investheavily in the research and development of VehicleEmission Control Strategies. Building upon thefoundation laid by PCV, the two-way and three-way catalyst, manufacturers further developedemissions control hardware. Such systems includedexhaust gas re-circulation, secondary air injection,fuel tank canister purge, spark timing adjustment,air/fuel ratio control biasing, fuel shut off under Figure 5.3 Malfunction indicator lamp symbols
  • 80. 64 Advanced automotive fault diagnosistend to use the engine symbol on an orangebackground. When the fault occurs the system stores a diag-nostic trouble code (DTC) that can be used to traceand identify the fault. The system will also storeimportant information that pertains to the operat-ing conditions of the vehicle when the fault wasset. A service technician is able to connect a diag-nostic scan tool or a code reader that will commu-nicate with the microprocessor and retrieve thisinformation. This allows the technician to diag-nose and rectify the fault, make a repair/replace-ment, reset the OBD system and restore thevehicle emissions control system to a serviceable Figure 5.4 New mass airflow sensor (Source: Bosch)status. As vehicles and their systems become morecomplex, the functionality of OBD is being within the cylinder. It may be that tailpipe emis-extended to cover vehicle systems and components sions are likely to rise beyond legislated limits.that do not have anything to do with vehicle emis- Also the MAF sensor is used by other emis-sions control. Vehicle body, chassis and accessories sions control systems on the vehicle – now thatsuch as air conditioning or door modules can now its input is unreliable it follows that those sys-also be interrogated to determine their service- tems are no longer working at their optimum levelsability as an aid to fault diagnosis. and may not work at all. This is the reason for the malfunction indication lamp (MIL) illumination,5.2.1 OBD scenario example which says, in as many words:Whilst driving, a vehicle owner observes that the An emissions control system/sub system orvehicle’s engine ‘lacks power’ and ‘jumps some- component has become unserviceable!times’. This is a problem often faced by techni- Visual inspection of the MAF sensor reveals thatcians in that customers often have no engineering it has become damaged beyond repair and needsor automotive knowledge and use lay terms to replacing. This is carried out, the techniciandescribe what is happening with a very complex clears the DTC from the OBD system memory,system. The driver does however report that the resets the system, and a short test drive later theMIL has been illuminated. diagnostic scan tool confirms that the DTC is no The technician connects a scan tool that can longer present. The road test also confirms thatcommunicate using an industry standard com- the previous drive issue is no longer apparent.munications protocol. The OBD code memory ischecked and data is presented in a way that alsoconforms to a standard. DTC P1101 with thedescription ‘MAF sensor out of self test range’ is 5.2.2 Origins of OBD in the USAstored in memory, which means that the OBD The previous example relates to the current situ-System Component Monitor has identified the ation, but when OBD was first introduced stand-mass airflow (MAF) sensor circuit voltage as ards and practices were less well defined.outside an acceptable range (Figure 5.4). Manufacturers developed and applied their own Upon confirming the fault the system was systems and code descriptions. This state ofsmart – it defaulted to a ‘safe’ value of mass air- affairs was obviously undesirable since none fran-flow, a concept know as failure mode effects chised service, and repair centres had to under-management (FMEM) to allow the driver to take stand the various subtleties of each system; thisthe vehicle to a place of repair. Whilst this meant having different scan tools, as well as aFMEM value was a good short-term solution it is multitude of leads, manuals and connectors. Thisnot a sufficient substitute for the full functional- made diagnostics unwieldy and expensive. Thisity of a serviceable MAF sensor. stage became known as ‘OBD1’, the first stage of Since the MAF sensor determines the mass air- OBD introduction.flow going into the engine intake it will be impos- In the late 1980s the Society of Automotivesible for the system to run at the optimum air/fuel Engineers (SAE) defined a list of standardratio for efficient burning of the air/fuel charge practices and recommended these to the
  • 81. On-board diagnostics 65 P1101 Fault Nature 01 – Numbers often System Designation viewed together, P – Powertrain describe ‘what is wrong’ B – Body C – Chassis U – Undesignated Indicated Sub System 1 – Fuel or Air/Fuel – MAF 2 – Fuel control – injectors DTC Type 3 – Ignition or misfire 0 – Mandated description 4 – Emissions control – catalyst 1– Manufacturer specific 5 – Engine/Vehicle speed description 6 – Microprocessor 7 – Transmission 8 – Transmission 9 – SAE designated 0 – SAE designated Figure 5.5 P Code compositionEnvironmental Protection Agency (EPA). The instrumentation, or even in-car entertainment orEPA acknowledged the benefits of these stand- telematics.ards and recommendations, and adopted them. In C Codes are requested by the microprocessorcombination, they changed the shape and applica- controlling the chassis systems that control vehi-tion of OBD. The recommendations included cle dynamics such as ride height adjustment, trac-having a standard diagnostic connector, a stand- tion control, etc.ard scan tool and a communications protocol that The four numbers that follow the letter detailthe standard scan tool could use to interface with information pertaining to what sub-system declaredthe vehicle of any manufacturer. the code. Using the example from before, see The standard also included mandatory struc- Figure 5.5.tures and descriptions for certain emission controlsystem/component defects. These were called ‘P0’ 5.2.4 European on-boardCodes. Manufacturers were still free to generatetheir own ‘manufacturer specific code descriptions’ diagnostics and global adoptionknown as ‘P1’ Codes. This phase of implementa- Europe was not immune to the environmentaltion became known as OBD2, and was adopted for issues associated with smog. As mentioned earlier,implementation by 1st January 1996. a major smog episode occurred in London in late 1952; this lasted for five days and resulted in about 4000 deaths. In 1956, the UK government passed5.2.3 P Code composition its first Clean Air Act, which aimed to controlThe diagnostic trouble code (DTC) is displayed domestic sources of smoke pollution.as a 5-character alphanumeric code. The first In 1970 the then European Community adoptedcharacter is a letter that defines which vehicle directive 70/220 EEC – ‘Measures to be takensystem set the code be it Powertrain, Body, or against Air Pollution by Emissions from MotorChassis. Vehicles’. This basically set the foundation for future legislation to curb motor vehicle pollution● P – means Powertrain System set the code in Europe. This Directive was amended over the● B – means Body System set the code next three decades when in October 1998 the● C – means Chassis System set the code amendment 98/69/EC ‘On-Board Diagnostics● U – is currently unused but has been ‘stolen’ (OBD) for Motor Vehicles’ was adopted, which to represent communication errors added Annex XI to the original 70/220 document. Annex XI details the functional aspects of OBD P Codes are requested by the microprocessor for motor vehicles in Europe and across the Globe.controlling the powertrain or transmission and This became known as EOBD.refer to the emissions control systems and theircomponents. B Codes are requested by the microprocessor 5.2.5 Summarycontrolling the body control systems. Collectively A major contributing factor to environmental healththese are grouped as lighting, air conditioning, issues in the Unites States was found to be motor
  • 82. 66 Advanced automotive fault diagnosisvehicle emissions pollution. Scientific studies by Board (CARB) in 1988 and later federally by thegovernment sponsored academic establishments Clean Air Act Amendments of 1990. This meantand vehicle manufacturers then took place over that the enforcing body, the environmental protec-several years. Legislative bodies were formed tion agency, requires that States have to developwhich later developed and enacted the vehicle state implementation plans (SIPs) that explain howemissions control legislation, which forced vehicle each state will implement a plan to clean up pollu-manufacturers to develop control strategies and tion from sources including motor vehicles. Oneincorporate them within their production vehicles. aspect of the requirement is the performance of As microprocessor technologies became more on-board diagnostic (OBD) system checks as partadvanced and commercially viable, the legisla- of the required periodic inspection.tion was augmented to include a self-diagnosing In order to be compliant with legislation andonboard diagnostic system, which would report still sell vehicles, manufacturers needed to engin-when the emissions control system was unser- eer ‘early warning’ monitoring sub-systems thatviceable. First attempts by manufacturers to use would determine when emission control systemssuch a system were applied unilaterally which had malfunctioned to the extent that tailpiperesulted in confusion, regenerative work and a emissions had (or were likely to in the long-term)poor reception of the OBD (now termed OBD1) exceed a legislated level. On-board diagnosticconcept. A revision of the legislation adopted ‘monitors’ were derived for this purpose.SAE recommended standards, which resulted inthe OBD (now termed OBD2) system becoming 5.3.3 Component monitoringlargely generic and applicable across the wholerange of vehicle manufacturers. The emission control systems integral with the As environmental activism spread across to vehicle employ many sensors and actuators. AEurope, vehicle manufacturers realised they had software program housed within a microproces-to support a philosophy of sustainable growth. sor defines their actions.Similar legislation was adopted and European The ‘component monitor’ is responsible forOBD (EOBD) manifested itself in a form very determining the serviceability of these sensors andsimilar to that observed in the United States. actuators. Intelligent component drivers linked to the microprocessor have the ability to enable/dis- able sensors/actuators, and to receive signals. The analogue inputs from the sensors are converted to5.3 Petrol/gasoline digital values within the microprocessor.on-board diagnostic In combination with these component drivers, the microprocessor possesses the functionality tomonitors detect circuit faults on the links between micro- processor and component. In addition, rationality5.3.1 Introduction tests can be performed to determine whether theThis section will cover the fundamentals of some sensor is operating out of range of its specification.of the on-board diagnostic systems employed onmainstream petrol/gasoline vehicles. The concept 5.3.4 Rationality testingof how the OBD system is divided into a series of Rationality tests can be performed on such sensorssoftware based serviceability indicators known as as the mass airflow (MAF) sensor and throttle‘OBD monitors’, is also covered. body. For example, the MAF is tested by observing its output value in comparison to a ‘mapped’ value5.3.2 Legislative drivers normalised by throttle position and engine speed. The map or table contains expected MAF outputIn Europe – The European Directive 70/220 EEC values for the engine speed/throttle set point.was supplemented by European Directive 98/ Should the MAF output lie outside of an accept-69/EC (Year: 1998. OJ Series: L – OJ Number: able range (threshold) of values for that engine350/1). This introduced legislation mandating the speed/throttle set point, then a fault is reported.use of on-board diagnostic systems in passengervehicles manufactured and sold after January 1st2001. 5.3.5 Circuit testing In the USA – Legislation was first introduced The component monitor is capable of monitoringin California by the California Air Requirements for circuit faults. Open circuits, short circuits to
  • 83. On-board diagnostics 67ground or voltage can be detected. Many manu- As the catalyst’s ability to store oxygen (andfacturers also include logic to detect intermittent hence perform three-way catalysis) deteriorates,errors. the oxygen sensor downstream of the sensor will respond to the oxygen in the exhaust gas stream and its signal response will exhibit a characteris-5.3.6 Catalyst monitor tic similar to the upstream oxygen sensor.The purpose of the catalyst is to reduce tailpipe/ An algorithm within the microprocessorexhaust emissions. The ‘catalyst monitor’ is analyses this signal and determines whether theresponsible for determining the efficiency of the efficiency of the catalyst has degraded beyond thecatalyst by inferring its ability to store oxygen. point where the vehicle tailpipe emissions exceedThe method favoured most by the majority of legislated levels (Figure 5.7). If the microproces-manufacturers is to fit an oxygen sensor before sor determines that this has occurred then a mal-and after the catalyst (Figure 5.6). function and a DTC is reported. Repeat detections Exhaust gas sensors (Air/fuel ratio sensor, Oxygen sensor) Catalyst Figure 5.6 Exhaust gas oxygen (Ceramic substrate) sensors positioned pre and post catalyst (Source: www. Engine ECU globaldensoproducts.com) 1.03 Lambda before cat Lambda after cat 1.02 1.01 Lamda [v] 1 0.99 0.98 0.97 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 Time [s]Figure 5.7 Upstream and downstream exhaust gas sensor activity – good catalyst (Source: SAE 2001-01-0933 New Cat PreparationProcedure for OBD2 Monitoring Requirements)
  • 84. 68 Advanced automotive fault diagnosis 1.03 Lamda before cat Lamda after cat 1.02 1.01 1 0.012 0.99 0.98 0.97 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 Time [s]Figure 5.8 Upstream and downstream exhaust gas sensor activity – failed catalyst (Source: SAE 2001-01-0933 New Cat PreparationProcedure for OBD2 Monitoring Requirements)of a failed catalyst will result in MIL illumination European legislation dictates that these checks(Figure 5.8). are not required. However, vehicles manufactured in the USA after 1996 and before 1999 generally employ a system that uses a pressure or vacuum5.3.7 Evaporative system system. This must be able to detect a leak in a hosemonitor or filler cap that is equivalent to that generated by a hole, which is 1 mm (0.40Љ) in diameter. VehiclesThe purpose of the evaporative (EVAP) emis- manufactured after 2000 must support diagnos-sions control system is to store and subsequently tics that are capable of detecting a 0.5 mm (0.20Љ)dispose of unburned hydrocarbon emissions thus hole.preventing them from entering the atmosphere.This is achieved by applying a vacuum across thefuel tank. The vacuum then causes fuel vapour tobe drawn through a carbon canister in which the 5.3.8 Fuel system monitoringhydrocarbon vapours are collected and stored. As vehicles accumulate mileage then so also During certain closed loop fuel control condi- do the components, sensors and actuators of thetions the microprocessor activates a solenoid con- emissions control systems. Mass airflow sensorstrolled ‘vapour management valve’. This allows become dirty and their response slows with age.the manifold vacuum to draw vapour from the car- Exhaust gas oxygen sensors also respond slowerbon canister along vapour lines, which terminate as they are subject to the in-field failure modesin the intake manifold. The fuel vapour is then such as oil and fuel contamination, thermal stresscombined and combusted with the standard air and general ageing. Fuel pressure regulators per-/fuel charge, the closed loop fuel control system form outside of their optimum capacity, fuel injec-caters for the additional air fuel ratio enrichment tors become slower in their response, and partialto ensure that stoichiometric fuelling continues. blockages mean that they deliver less and some- The evaporative system monitor is responsible times more fuel than requested.for determining the serviceability of the EVAP sys- If this component ageing were not compen-tem components and to detect leaks in the vapour sated for it would mean that the fuel system wouldlines. Most manufacturers check for fuel vapour not be able to maintain normal fuelling aroundleaks by employing a diagnostic that utilises a stoichiometric air fuel ratio as shown in Figurepressure or vacuum test on the fuel system. 5.9. The end result would be the potential to
  • 85. On-board diagnostics 69 1 2 4 6 5 Ps ∆p Pu 3 1 – Line from fuel tank to carbon canister. 4 – Canister-purge valve. 2 – Carbon canister. 5 – Line to intake manifold. 3 – Fresh air. 6 – Throttle valve. Ps–Intake-manifold pressure. ∆p–Difference between intake-manifold Pu–Atmospheric pressure. pressure and atmospheric pressure.Figure 5.9 Evaporative emissions control system (Source: Bosch)exceed emission limits. A lambda value of one is Referring to Figures 5.10 and 5.11, it can be seenrequired in order for the three-way catalyst to that when there is a component malfunction, whichwork. In addition to this, more severe fuelling causes the AFR in the exhaust stream to be rich,errors would cause noticeable effects in the per- then there is a need to adapt to this to bring theformance of the vehicle leading to customer AFR back into the region of stoichiometry. Thecomplaints and potential to damage the manufac- value of the long-term fuel trim correction mustturer’s brand image. decrease because less fuel is required. Should the This compensation strategy is known as adap- situation continue and the problem causing richtive learning. A dedicated piece of software con- AFR becomes slowly worse, then the error adap-tained within the ECU learns these deviations tion will continue with an ever-decreasing valueaway from stoichiometry, while the fuel system is for the long-term fuel trim being applied, learnedin closed loop control. They are stored in a mem- and stored in memory.ory that is only reset when commanded by a tech- The purpose of the fuel monitor is to deter-nician and which is also robust to battery changes. mine when the amount of long-term adaptive cor- These memory-stored corrections are often rection has reached the point where the systemtermed ‘long-term’ fuel corrections. They are often can no longer cope. This is also where long-termstored in memory as a function of air mass, engine fuel trim values reach a pre-defined or ‘calibrated’speed or engine load. limit at which no further adaption to error is An exhaust gas oxygen sensor detects the allowed. This limit is calibrated to coincide withamount of oxygen in the catalyst feed gas and exhaust tailpipe emissions exceeding legislatedthe sensor produces a voltage, which is fed back to levels. At this point, and when a short-term fuellingthe microprocessor. This is then processed to deter- error exceeds another ‘calibrated’ limit, a DTC ismine the instantaneous or ‘short-term’ fuel correc- stored and after consecutive drives the MI is illu-tion to be applied. This is done in order to vary the minated. The opposite occurs, with extra fuel beingfuel around stoichiometry and allow three-way added, via the long-term fuel trim parameter,catalysis to occur. should an error occur that causes the AFR at the The microprocessor then calculates the amount exhaust gas oxygen sensor to be lean.of fuel required using an equation, which is shownin its most basic form below. 5.3.9 Misfire monitor Air mass ϫ Long-term fuel trim When an engine endures a period of misfire, atFuel mass ϭ Sho rt-term fuel trim ϫ14.64 best tailpipe emissions will increase and at worst
  • 86. 70 Advanced automotive fault diagnosisVoltage characteristic of the Lambda-sensor signal Air-fuel mixture lean rich lean rich lean rich lean rich lean rich leanSensor-voltagecharacteristicLambda-correctionfactorRicherNeutral value 1.0 Figure 5.10 Rich AFR lambdaLeaner sensor signal fuelling error (Source: Time t Bosch)Cyclic change between mixture adaptation and adaptation of the cylinder-charge factorLambdacorrectionfactorRicherNeutral value 1.0LeanerAdaptionvariable Figure 5.11 Adaptive fuel strategy Time t in operation (Source: Bosch)catalyst damage and even destruction can occur.When misfire occurs, the unburned fuel and air is A ϭ Load at Neutral Idle B ϭ Load at Neutral 3000 rpmdischarged direct to the exhaust system where it C ϭ Load at Neutral Redlinepasses directly through the catalyst. D ϭ Load at 4" Hg Less than Vacuum Subsequent normal combustion events can Lcombust this air/fuel charge in something akin to o a Da bellows effect, which causes catalyst tempera- dtures to rise considerably. Catalyst damage fail- B Cure thresholds are package specific but are in theregion of 1000°C. The catalyst itself is a very A Negative Torque Disablementexpensive service item whether replaced by thecustomer or the manufacturer under warranty. Idle 3000 RPM Readline The misfire monitor is responsible for deter- Figure 5.12 Misfire enablement window (Ford Motor Company)mining when misfire has occurred, calculating therate of engine misfire and then initiating somekind of protective action in order to prevent cata-lyst damage. The misfire monitor is in operation throughout the revs range but European legislationcontinuously within a ‘calibrateable’ engine speed/ requires monitoring only up to 4500 rev/min.load window defined by the legislation (Figure The crankshaft sensor generates a signal as the5.12). The USA requires misfire monitoring wheel rotates and the microprocessor processes
  • 87. On-board diagnostics 71 EEEC Deviant Acceleration VRS Low Data Rate (Calculated by SW) (Crank Signal) Delta Times (PIP_DWN_DEL) Signal Misfire Conditioning SW EDIS Monitor Electronics SW CVRS PIP (Conditioned VRS) (Synthesised by SW) Figure 5.13 Crankshaft 36-1 Tooth Wheel Acceleration mounted wheel and sensor (Calculated by SW) source of angular acceleration (Source: Ford Motor Company)this signal to determine the angular acceleration The rate of misfire that will cause catalyst dam-of the crankshaft produced by each engine cylin- age varies as a function of engine speed and load.der when a firing event occurs. When a misfire Misfire rates in the region of 45% are required tooccurs the crankshaft decelerates and a cam pos- damage a catalyst at neutral idle whilst at 80%ition sensor identifies the cylinder that misfired. engine load and 4000 rev/min misfire rates in the Processing of the signal from the crank pos- region of only 5% are needed (Figure 5.14).ition sensor is not straightforward. A considerable A type B misfire is defined as that rate of mis-amount of post-processing takes place to filter the fire that will cause the tailpipe emissions to exceedsignal and disable monitoring in unfavourable legislated levels. This varies from vehicle to ve-conditions. The misfire monitor must learn and hicle and is dependent upon catalyst package. MIcater for the differences in manufacturing toler- operation is the same as for standard MI DTCs.ances of the crankshaft wheel and so has a spe-cific sub-algorithm for learning these differencesand allowing for them when calculating the angu- 5.3.10 Exhaust gas recirculationlar acceleration of the crankshaft (Figure 5.13).These correction factors are calculated during monitordeceleration, with the injectors switched off. They As combustion takes place within the engineshould be re-learned following driveline compo- cylinders, nitrogen and oxygen combine to formnent changes such as flywheel, torque converter, various oxides of nitrogen; collectively these arecrankshaft sensor, etc. termed NOx. NOx emissions can be reduced up The misfire monitor must be able to detect to a certain point by enriching the air/fuel ratiotwo types of misfire: beyond the point at which hydrocarbon (HC) and carbon monoxide (CO) emissions begin to● Type A misfire; increase. NOx emissions are generated as a func-● Type B misfire. tion of combustion temperature, so another wayA type A misfire is defined as that rate of misfire, to reduce these is to decrease the compressionwhich causes catalyst damage. When this occurs ratio which leads to other inefficiencies like poorthe MI will flash at a rate of 1 Hz and is allowed to fuel economy.stop flashing should the misfire disappear. The MI Most manufacturers employ an emissions con-will stay on steady state should the misfire re-occur trol sub-system known as exhaust gas recircula-on a subsequent drive and the engine operating tion (EGR). This by definition recirculates someconditions are ‘similar’ i.e. engine speed is within of the exhaust gases back into the normal intake375 rev/min, engine load is within 20%, and the charge. These ‘combusted’ gases cannot be burntengine’s warm-up status is the same as that under again so they act to dilute the intake charge. As awhich the malfunction was first detected (and no result, in-cylinder temperatures are reduced alongnew malfunctions have been detected). with NOx emissions (Figure 5.15).
  • 88. 72 Advanced automotive fault diagnosisFigure 5.14 System development screen showing type A misfire rates normalised by engine speed and load (Source: Ford MotorCompany) Electronic PCM vacuum regulator Fresh air inlet (EVR) VREF EVR SIG RTN VPWR EGR SIG DPFE Valve Intake Sensor EGR Tube DPFE Intake Manifold Side (IMS) Signal Orifice DPFE Exhaust Manifold Side (EMS) Signal ExhaustFigure 5.15 EGR system using differential pressure monitoring (Source: Ford Motor Company) The exhaust gas recirculation system monitor non-intrusive, such as a change in manifold pres-is responsible for determining the serviceability sure as EGR is flowed and then shut off.of the sensors, hoses, valves and actuators that One method monitors AFR excursions afterbelong to the EGR system. Manufacturers the EGR valve is opened and then closed as theemploy systems that can verify that the requested AFR becomes lean. Another system employs aamount of exhaust gas is flowing back into the differential pressure scheme that determines theengine intake. Methods can be both intrusive and pressure both upstream and downstream of the
  • 89. On-board diagnostics 73 Secondary Air Secondary Air Injection System Injection System OK Not OK U U t t Figure 5.16 Secondary airflow diagnostic monitoringexhaust to determine whether the requested flow Older systems support a belt driven mechan-rate is in effect. Yet another system employs a ical pump with a bypass valve for when second-temperature sensor, which reports the change in ary airflow is not required. Modern vehiclestemperature as EGR gases flow past the sensor. employ an electric air pump operated by the engineThe temperature change will be mapped against management ECU (powertrain control modulethe amount of EGR flowing so when an amount [PCM]) via relays.of EGR is requested then the flow rate is inferred The secondary air monitor is responsible forby measuring the change in temperature. determining the serviceability of the secondary air system components (Figure 5.16). Most strategies monitor the electrical components and ensure the5.3.11 Secondary air monitor system pumps air when requested by the ECU. ToThe exhaust system catalyst is not immediately check the airflow, the ECU observes the responseoperative following a start where the engine and of the exhaust gas oxygen sensor after it com-exhaust system is cool. Temperature thresholds mands the fuel control system to enter open loopabove which the catalyst is working, and three-way control and force the AFR to become rich. Thecatalysis is occurring, vary as a function of the secondary air pump is then commanded on andexhaust gas system package. Typically, this ‘light the ECU determines the time taken for the exhaustoff’ point occurs at temperatures of about 260°C/ gas oxygen sensor to indicate a lean AFR. If this500°F. Some manufacturers employ electrically time exceeds a calibrated threshold then a diag-heated catalysts to reach this temperature rapidly nostic trouble code is stored.but these are expensive to manufacture and replace. Most manufacturers rely on the exhaust gases 5.3.12 Exhaust gas oxygenas a source of heat in order to bring the catalystup to light off temperature. When the vehicle is sensor monitorstarted from cold the AFR is rich; this is required The outside surface of the ceramic measuringto ensure a stable engine start for cold pull-away. tube protrudes into the exhaust gas flow, and theFrom an emissions perspective, the impact is inner surface is in contact with the outside airobserved in the production of HC and CO in the (Figure 5.17).exhaust stream because the exhaust system cata- At high temperatures a zirconia type sensorlyst has not reached light off. allows the passage of oxygen ions between the two The secondary air system uses a pump, which platinum electrodes and a voltage is generated. Theadds more air into the exhaust stream at a point voltage is proportional to the relationship betweenbefore the catalyst following a cold start. The the residual oxygen in the exhaust gas and that ofsecondary air combusts the HC in the catalyst, the surrounding air.generating heat, which in turn, promotes light off When the AFR of the exhaust gas is rich there isand further emissions reduction. less free oxygen at the outer electrode with more
  • 90. 74 Advanced automotive fault diagnosis 5.4.1 Introduction In the mid-1980s the US environmental protection agency (EPA) introduced a policy which made the use of on-board diagnostics (OBD) compulsory for vehicles in the United States. This was fol- lowed by similar requirements introduced by the California Air Resources Board (CARB), which promoted the development of technology such that the diagnostic technician would have access to information stored within the engine electronic control unit (ECU). This information, relating to faults that have occurred and that have beenFigure 5.17 Exhaust gas oxygen sensor – zirconia type logged and stored in the ECU memory, signifi-(Source: Bosch Press) cantly assists in fault diagnosis and rectification. The main reason for this legislation is the require- ments to reduce exhaust emissions. The basicavailable at the inner electrode. This results in a objectives are:positive voltage of between 0.6 V and 0.8 V beinggenerated. When the AFR of the exhaust gas is ● to improve emissions compliance by alertinglean there is little difference in the oxygen concen- the driver immediately to a fault conditiontrations and a low voltage is produced. This volt- whilst driving;age is processed by the microprocessor as part of a ● to assist repair/diagnostics technicians in identi-closed loop fuel control system which in-turn fying system faults and faulty components inensures three-way catalysis. The exhaust gas oxy- the emission control system.gen sensor monitor is responsible for determining On-board diagnostic monitoring applies to sys-the serviceability of all of the oxygen sensors and tems which are most likely to cause an increasetheir heater elements. Manufacturers employ an in harmful exhaust emission, namely:algorithm similar to the component monitor todetect open circuits and other common shorts. ● All main engine sensors Additional diagnostics exist for when the sen- ● Fuel systemsor is ‘stuck’ lean or rich. The monitor waits for ● Ignition systemthe sensor to ‘switch’ as it normally would and if ● Exhaust gas recirculation (EGR) systemthis does not occur within a calibrated timeframethen a DTC is reported and MI illumination if the The system uses information from sensors tofault is apparent on consecutive drives. judge the performance of the emission controls Diagnostics also exist for when a sensor but these sensors do not directly measure theresponse is slowed. As the sensor ages it continues vehicle emissions.to switch but with a much reduced amplitude and An important part of the system, and the mainfrequency. When this occurs it induces fuelling driver information interface, is the ‘check engine’errors. Manufacturers are obliged to report when warning light. Also known as the malfunction indi-the performance of the sensor has been degraded cator light (MIL). This is the main source of feed-to the point where exhaust emissions exceed legis- back to the driver to indicate if an engine problemlated limits. has occurred or is present. When a malfunction or fault occurs the warning light illuminates to alert the driver. Additionally the fault is stored in ECU memory. If normal condition is re-instated, the5.4 On-board diagnostics – light extinguishes but the fault remains logged toa second perspective aid diagnostics. Circuits are monitored for open or short circuits as well as plausibility. When a Authors note: The section on OBD repeats some of malfunction is detected, information about the the information supplied previously but because this is such an important subject I decided that looking at it malfunctioning component is stored. from two different view points would be useful. I am An additional benefit allows the diagnostic most grateful to Dave Rogers (www.autoelex.co.uk) technician to be able to access fault information for his excellent contribution to this chapter. and monitor engine performance via data streamed
  • 91. On-board diagnostics 75 Californias Air Basins & Counties1943: first smog alarm in LA Air Basin N County Northeast Plateau1950: 4,5 Mio. vehicles in california Sacramen to Valley W E1952: Dr. Arie Haagen-Smit analyses the reasons for smog development North Coast S Mountain counties1960: 8 Mio. vehicles in California Lake Tahoe Lake County1961: introduction of crankcase ventilation (PCV) San Joaquin Valley1966: Federal Clean Air Act San Francisco Bay Great Basin Valleys1967: foundation of CARB, Chairman: Haagen-Smit1970: foundation of EPA North Central Coast1980: 17 Mio. vehicles in California Mojave Desert1988: CARB decides OBD II for 1994 MY South Central Coast1990: number of smog days goes down, CARB decides LEV and ZEV – program South Coast Salton Sea1995: 26 Mio. vehicles in California San Diego County1996: Ozon-pollution 59% below 1965, number of smog days 94% below 1975Figure 5.18 History of CARB Emission legislation activitydirectly from the ECU whilst the engine is running the current OBD2 standard. The OBD2 require-(on certain vehicles). This information can be ment applies to all cars sold in the United Statesaccessed via various scan tools available on the from 1996. EOBD is the European equivalentmarket and is communicated in a standardised of the American OBD2 standard, which appliesformat so one tool (more or less!) works with all to petrol cars sold in Europe from 2001 (andvehicles. The data is transmitted in a digital form diesel cars three years later).via this serial interface. Thus data values are trans- OBD2 (also OBDII) was developed to address themitted as data words and the protocol used for this shortcomings of OBD1 and make the system moredata stream has to be known in order to evaluate user friendly for service and repair technicians.the information properly. The benefits of having an OBD system arethat it: 5.4.2 OBD2 Even though new vehicles sold today are cleaner● encourages vehicle and engine manufacturers than they have ever been, the millions of cars on to have a responsible attitude to reducing the road and the ever increasing miles they travel harmful emissions from their engines via the each day make them our single greatest source of development of reliable and durable emission harmful emissions. While a new vehicle may start control systems; out with very low emissions, infrequent maint-● aids diagnosis and repair of complex elec- enance or failure of components can cause the tronic engine and vehicle control systems; vehicle emission levels to increase at an undesir-● reduces global emissions by identifying and able rate. OBD2 works to ensure that the vehicles highlighting immediately to the driver or user remain as clean as possible over their entire life emission control systems in need of repair; (Figure 5.19). The main features of OBD2 are,● provides ‘whole life’ emission control of the therefore, as follows. engine;● on-board diagnostics, or OBD, was the name ● Malfunction of emission relevant components given to the early emission control and engine- to be detected when emission threshold values management systems introduced in cars. There are exceeded. was no single standard – each manufacturer ● Storage of failures and boundary conditions in often using quite different systems (even the vehicle’s fault memory. between individual car models). OBD systems ● Diagnostic light (MIL – Malfunction Indicator have been developed and enhanced, in line with Light) to be activated in case of failures. United States government requirements, into ● Read out of failures with generic scan tool.
  • 92. 76 Advanced automotive fault diagnosis High Accelerator- pressure Injector pedal module Carbon canister pump Fuel rail Ignition coil Canister Pressure control Phase sensor purge valve valve Oxygen Fuel pressure sensor Air-mass meter with Temp. Throttle Intake- sensor (LSU) temperature sensor sensor device manifold Knock (EGAS) sensor sensor Pre-catalyst BOSCH EGR-valve Speed Exhaust-gas sensor temperature sensor Electronic NOx control unit catalyst Diagnosis interface Delivery module incl. Malfunction indicator lamp low pressure pump Oxygen Immobiliser Bosch components specifically for DE sensor CAN Bosch components (LSF)Figure 5.19 OBD2 system showing the main components of a gasoline direct injection system (Source: Bosch Press)The increased power of micro controllers (CPUs) The main features of an OBD2 compliant systemin ECUs has meant that a number of important (as compared to OBD1) are:developments could be added with the introduc- ● pre and post-catalyst oxygen sensors to moni-tion of OBD2. These include Catalyst efficiency tor conversion efficiency;monitoring, misfire detection, canister purge and ● much more powerful ECU with 32bit processor;EGR flow rate monitoring. An additional benefit ● ECU Map data held on EEPROMS such thatis the standardisation of diagnostic equipment they can be accessed and manipulated via aninterfaces. external link. No need to remove ECU from For OBD1 each manufacturer applied speci- vehicle for software updates or tuning;fic protocols. With the introduction of OBD2 a ● more sophisticated EVAP system, can detectstandardised interface was developed with a stand- minute losses of fuel vapour;ard connector for all vehicles, and a standardised ● EGR systems with feedback of position/flowtheory for fault codes relating to the engine and rate;powertrain (more about this later). This meant that ● sequential fuel injection with MAP (Manifoldgeneric scan tools could be developed and used in Air Pressure) and MAF (Mass Air Flow) sens-the repair industry by diagnostic technicians to ing for engine load.aid troubleshooting of vehicle problems. Another feature of OBD2 is that the pre-scribed thresholds at which a fault is deemed to 5.4.3 EOBDhave occurred are in relation to regulated emis-sion limits. The basic monitor function is: EOBD is an abbreviation of European on-board diagnostics. All petrol/gasoline cars sold in Europe● monitoring of catalyst efficiency, engine misfire since 1 January 2001, and diesel cars manufactured and oxygen sensors function such that crossing from 2003, must have on-board diagnostic sys- a threshold of 1.5 times the emission limit will tems to monitor engine emissions. These systems record a fault; were introduced in line with European directives to● monitoring of the evaporation control sys- monitor and reduce emissions from cars. All such tem such that a leak greater than the equiva- cars must also have a standard EOBD diagnostic lent leak from a 0.04 inch hole will record socket that provides access to this system. The a fault. EOBD standard is similar to the US OBD2
  • 93. On-board diagnostics 77 Table C Emission limits table for comparison Legislation OBD Malfunction Limit (grams/km) HC CO NOx Pm EPA у1.5 times the applicable federal standard EPA – Method Multiplicative relative to limits CARB 1 and 2 у1.5 times the relevant CARB emission limits CARB 1 and 2 – Method Multiplicative relative to limits EOBD Positive lgn. 2000 0.40 3.20 0.60 – EOBD Diesel 2003 0.40 3.20 1.20 0.18 EOBD Positive lgn. 2005 0.20 1.40 0.30 – EOBD Diesel 2008 (for indication only) 0.30 2.40 0.90 0.14 EOBD – Method Absolute limitsTable D Cars not exceeding 2.5 tonnes laden Number Fuel Directive Limit values (gm/km) Implementation dates of seats CO HC NOx HC ϩ NOx PM Type approval In-useEuro III up to 9 P 98/69/EC 2.30 0.20 0.15 – – 01/01/00 01/01/01 up to 9 D 98/69/EC 0.64 – 0.50 0.56 0.05 01/01/00 01/01/01 Note (i) D 98/69/EC 0.80 – 0.65 0.72 0.07 01/01/01 01/01/02 Note (ii) D 98/69/EC 0.95 – 0.78 0.86 0.10 01/01/01 01/01/02Euro IV up to 9 P 98/69/EC 1.00 0.10 0.08 – – 01/01/05 01/01/06 up to 9 D 98/69/EC 0.50 – 0.25 0.30 0.025 01/01/05 01/01/06Key: P – Petrol, D – Diesel, di – direct injection, CO – Carbon Monoxide, HC – Hydrocarbons, NOx – Oxides of Nitrogen, PM –Particulate massNote (i) – Temporary concession for diesel cars over 2.0 tonnes laden weight which are off-road or more than six seats (unladen weightfrom 1206 to 1660 kg). Concession ceased on 31/12/02.Note (ii) – Temporary concession for diesel cars over 2.0 tonnes laden weight which are off-road or more than six seats (unladen weightover 1660 kg). Concession ceased on 31/12/02.Source: Vehicle Certification Agency manual, May 2005.Table E Heavy motor car (more than 2.5 tonnes laden or more than six seats). Unladen weight between 1151 and 1600 kg Number Fuel Directive Limit values (gm/km) Implementation dates of seats CO HC NOx HC ϩ NOx PM Type approval In-useEuro III up to 9 P 98/69/EC 4.17 0.25 0.18 – – 01/01/01 01/01/02 up to 9 D 98/69/EC 0.80 – 0.65 0.72 0.07 01/01/01 01/01/02Euro IV up to 9 P 98/69/EC 1.81 0.13 0.10 – – 01/01/06 01/01/07 up to 9 D 98/69/EC 0.63 – 0.33 0.39 0.04 01/01/06 01/01/07Key: P – Petrol, D – Diesel, di – direct injection, CO – Carbon Monoxide, HC – Hydrocarbons, NOx – Oxides of Nitrogen,PM – Particulate massstandard. In Japan, the JOBD system is used. The ● January 2004 OBD for all new Diesel vehiclesimplementation plan for EOBD was as follows: PC/LDV; ● January 2005 OBD for all new Diesel vehicles● January 2000 OBD for all new Petrol/Gasoline HDV. vehicle models;● January 2001 OBD for all new Petrol/Gasoline The EOBD system is designed, constructed and vehicles; installed in a vehicle such as to enable it to iden-● January 2003 OBD for all new Diesel vehicle tify types of deterioration or malfunction over models PC/LDV; the entire life of the vehicle. The system must be
  • 94. 78 Advanced automotive fault diagnosisTable F Heavy motor car (more than 2.5 tonnes fully laden or more than six seats). Unladen weight over 600 kg Number Fuel Directive Limit values (gm/km) Implementation Dates of seats CO HC NOx HC ϩ NOx PM Type Approval In-useEuro III up to 9 P 98/69/EC 5.22 0.29 0.21 – – 01/01/01 01/01/02 up to 9 D 98/69/EC 0.95 – 0.78 0.86 0.10 01/01/01 01/01/02Euro IV up to 9 P 98/69/EC 2.27 0.16 0.11 – – 01/01/06 01/01/07 up to 9 D 98/69/EC 0.74 – 0.39 0.46 0.06 01/01/06 01/01/07Key: P – Petrol, D – Diesel, di – direct injection, CO – Carbon Monoxide, HC – Hydrocarbons, NOx – Oxides of Nitrogen,PM – Particulate massNote: The test procedure for Euro III and Euro IV is more severe than that for Euro I and Euro II. This results in some emission levelshaving an apparent increase when in fact they are more tightly controlled.designed, constructed and installed in a vehicle Compression ignition enginesto enable it to comply with the requirements dur- ● Where fitted, reduction in the efficiency of theing conditions of normal use. catalytic converter. In addition, EOBD and OBD2 allow access ● Where fitted, the functionality and integrity ofto manufacturer-specific features available on the particulate trap.some OBD2/EOBD compliant scan tools. This ● The fuel injection system electronic fuel quan-allows additional parameters or information to be tity and timing actuator(s) is/are monitored forextracted from the vehicle systems. These are in circuit continuity and total function failure.addition to the normal parameters and information ● Other emission control system components oravailable within the EOBD/OBD2 standard. These systems, or emission-related powertrain com-enhanced functions are highly specific and vary ponents or systems which are connected to awidely between manufacturers. computer, the failure of which may result in tailpipe emission exceeding the specified limitsEOBD monitoring requirements on given. Examples of such systems or compo- nents are those for monitoring and control of airthe vehicle massflow, air volumetric flow (and tempera-The monitoring capabilities of the EOBD system ture), boost pressure and inlet manifold pressureare defined for petrol/gasoline (spark ignition) (and relevant sensors to enable these functionsand diesel (compression ignition) engines. The to be carried out).following is an outline. ● Any other emission-related powertrain com- ponent connected to a computer must be moni-Spark ignition engines tored for circuit continuity.● Detection of the reduction in the efficiency of 5.4.4 Features and technology of the catalytic converter with respect to emis- sions of HC only. current systems● The presence of engine misfires in the engine To avoid false detection, the legislation allows operation region within the following bound- verification and healing strategies. These are out- ary conditions. lined as follows.● Oxygen sensor deterioration.● Other emission control system components or MIL activation logic for detected systems, or emission-related powertrain com- ponents or systems which are connected to a malfunctions computer, the failure of which may result in To avoid wrong detections the legislation allows tailpipe emission exceeding the specified limits. verification of the detected failure. The failure is● Any other emission-related powertrain com- stored in the fault memory as a pending code ponent connected to a computer must be moni- immediately after the first recognition but the tored for circuit continuity. MIL is not activated. The MIL will be illuminated● The electronic evaporative emission purge in the third driving cycle, in which the failure has control must, at a minimum, be monitored for been detected; the failure is then recognised as a circuit continuity. confirmed fault.
  • 95. On-board diagnostics 79 Speed (km/h) Part One Part Two 120 100 80 Elementary urban cycle 60 40 20 ES BS 0 0 Time(s) 195 195 195 195 400 1180Figure 5.20 New European driving cycle (NEDC)MIL healing ● closed or open loop operation (if available);The MIL may be de-activated after three subse- ● the fault code which caused the data to bequent sequential driving cycles during which the stored.monitoring system responsible for activating theMIL ceases to detect the malfunction and if no 5.4.5 OBD cyclesother malfunction has been identified that wouldindependently activate the MIL. Directive 98/69/EC defines three different types of driving cycle:Healing of the fault memory 1. Type 1 test (the NEDC, (Figure 5.20)) definedThe OBD system may erase a fault code, dis- in Annex III, Appendix 1 of the directive;tance travelled and freeze-frame information if 2. A ‘driving cycle consists of engine start-up, athe same fault is not re-registered in at least forty driving mode where a malfunction would beengine warm-up cycles. detected if present, and engine shut off; 3. A ‘warm-up cycle’ means sufficient vehicleFreeze frame operation such that the coolant temperatureThis is a feature that can assist in the diagnosis of has risen by at least 22°C from engine startingintermittent faults. Upon determination of the and reaches a minimum temperature of 70°C.first malfunction of any component or system,‘freeze frame’ engine conditions present at thetime must be stored in the computer memory. 5.4.6 Monitors and readinessStored engine conditions must include, but are flagsnot limited to: An important part of the OBD system is the system● calculated/derived load value; monitors and associated readiness flags (Figure● engine speed; 5.21). These readiness flags indicate when a mon-● fuel trim values (if available); itor is active. Certain monitors are continuous, for● fuel pressure (if available); example, misfire and fuel system monitors.● vehicle speed (if available); Monitor status (Ready/Not Ready) indicates● coolant temperature; if a monitor has completed its self evaluation● intake manifold pressure (if available); sequence. System monitors are set to ‘Not Ready’
  • 96. 80 Advanced automotive fault diagnosis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Figure 5.22 Sixteen Pin DLC OBD2/EOBD connector occur with the engine electronic control system; particularly faults that could affect the emission control system and this is one of its primary functions. For the diagnostic technician this is a powerful feature which can clearly assist in locating and rectifying problems on the vehicle when they occur. The diagnostic socket used by systems con- forming to EOBD/OBD2 standards (Figure 5.22) should have the following pin configuration:Figure 5.21 System monitors (marked as ‘Complete’) and livedata shown in scan tool 1. Ignition positive supply 2. Bus ϩ Line, SAE J1850 (PWM) 3. Manufacturer’s discretionif cleared by scan tool and/or the battery is discon- 4. Chassis groundnected. Some of the monitors must test their com- 5. Signal groundponents under specific, appropriate preconditions. 6. CAN bus H● The evaporative system monitor has tempera- 7. K Line ture and fuel fill level constraints. 8. Manufacturer’s discretion● The misfire monitor may ignore input on 9. Manufacturer’s discretion rough road surfaces to prevent false triggers. 10. Bus – Line (PWM)● The oxygen sensor heater must monitor from 11. Manufacturer’s discretion a cold start. 12. Manufacturer’s discretion 13. Manufacturer’s discretionMost other system monitors are not continuous 14. CAN bus Land are only active under certain conditions. If 15. L line or second K linethese conditions are not fulfilled then the readi- 16. Vehicle battery positive.ness flag for that monitor is set to ‘not ready’.Until the readiness flags are set appropriately. It With the introduction of OBD2 and EOBD thisis not possible to perform a test of the OBD sys- feature was made even more powerful by makingtem and its associated components. it more accessible. Standardisation of the interface There is no universal drive cycle that is guaran- connector known as the diagnostic link connectorteed to set all the system monitors appropriately for (DLC) and communication protocol allowed thea test of the OBD system. Most manufacturers and development of generic scan tools, which could beeven cars have their own specific requirements and used on any OBD compliant vehicle.irrespective of this, there are still some specific Most systems in use involve two types of codes.vehicles that have known issues when trying to set The generic codes associated with the OBD stand-readiness flag status. As mentioned above, some ard and manufacturer specific codes. The genericallowance has been made for vehicles of model codes have a specific structure that allows easyyear 1996 to 2000 which can show two readiness identification and are common across all manufac-flags to be ‘not ready’. After this, 2001 onwards, turers (Figure 5.23). That is, a certain fault codeone readiness flag is allowed to be ‘not ready’ prior means the same thing on any vehicle, irrespectiveto a test. of the manufacturer (Figure 5.24). All basic scan tools are capable of reading these generic codes. The second type of code available is a manu-5.4.7 Fault codes facturer specific code. These are enhanced codesAn integral feature of the OBD system is its abil- which can give additional information aboutity to store fault codes relating to problems that the engine, vehicle and powertrain electronic
  • 97. On-board diagnostics 81 P0100 Mass or Volume Air Flow Circuit Malfunction P0101 Mass or Volume Air Flow Circuit Range/Performance Problem Fault (00-99) P0102 Mass or Volume Air Flow Circuit Low Input P0103 Mass or Volume Air Flow Circuit High Input P0104 Mass or Volume Air Flow Circuit Intermittent 1-Fuel and Air Metering P0105 Manifold Absolute Pressure/Barometric Pressure Circuit Malfunction 2-Fuel and Air Metering (Injection Circuit) P0106 Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance Problem 3-Ignition Systems or Misfire P0107 Manifold Absolute Pressure/Barometric Pressure Circuit Low Input 4-Auxiliary Emission Controls P0108 Manifold Absolute Pressure/Barometric Pressure Circuit High Input 5-Vechicle Speed Control and Idle Control System P0109 Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent 6-Computer Output Circuit P0110 Intake Air Temperature Circuit Malfunction 7-Transmission P0111 Intake Air Temperature Circuit Range/Performance Problem 8-Transmission P0112 Intake Air Temperature Circuit Low Input P0113 Intake Air Temperature Circuit High Input P0114 Intake Air Temperature Circuit Intermittent 0-SAE P0115 Engine Coolant Temperature Circuit Malfunction 1-MFG P0116 Engine Coolant Temperature Circuit Range/Performance Problem P0117 Engine Coolant Temperature Circuit Low Input B-Body P0118 Engine Coolant Temperature Circuit High Input C-Chassis P0119 Engine Coolant Temperature Circuit Intermittent P-Powertrain U-Network Figure 5.24 Example fault codesFigure 5.23 Structure of generic codes Crank 615 610 Normal Firing Pulse Speed At 605 Idle 600 595 With Total Misfire°Crank rotation 0° 120° 240° 360° 480° 600° 720° #1 #2 #3 #4 #5 #6 #1 Cylinder Cylinder Cylinder Cylinder Cylinder Cylinder Cylinder Fires Fires Fires Fires Fires Fires Fires Crank position sensor 2 34 Pulses 2 Missing Missing Cam position Teeth Teeth sensor Figure 5.25 Misfire detection via crank sensorsystems and vary widely between manufacturers. these events, and integrates them over time toTypically they will cover non-emission related determine if this is a recurring problem whichcomponents; for example, ABS, SRS, etc. In would cause an emission violation or just a singleorder to be able to use these enhanced codes it is event. If the problem occurs over two consecutivenecessary to have the relevant information avail- trips, the MIL will illuminate to alert the driver.able from the manufacturer (as to identification A number of strategies for achieving this areof the codes). In addition, the relevant software available.or firmware must be available on the scan devicesuch that it can read these additional codes. Crank speed fluctuation A misfire event in a cylinder results in a lost power stroke. The gap in the torque output of the engine5.4.8 Misfire detection and a consequential momentary deceleration ofA small engine misfire can raise emissions signif- the crankshaft can be detected using the crank-icantly. If engine misfire occurs in excess of shaft position sensor (Figure 5.25). By closelyabout 17% of the time, permanent catalyst dam- monitoring the speed and acceleration of theage will occur. This clearly shows the importance crankshaft misfiring cylinders can be detected.of identifying misfire to keep engine emissions This technology is very commonly used in OBDlow (both short and medium term). The OBD sys- systems to detect non-firing cylinders that cantem monitors individual cylinder misfires, counts cause harmful emissions and catalyst damage.
  • 98. 82 Advanced automotive fault diagnosis There are a number of technical challenges that mounted directly above the spark plug (Figurehave to be overcome with this technique; the 5.26). Eliminating the distributor and high-voltageaccuracy achieved and reliability of the system is leads helps promote maximum energy transfervery dependent on the algorithms used for signal to the spark plug to ignite the mixture. In thisprocessing and analysis. Under certain condi- system the spark plug is not only used as a devicetions, misfire detection can be difficult; particu- to ignite the air/fuel mixture, but is also used aslarly at light load with high engine speed. Under an in-cylinder sensor to monitor the combustionthese conditions the damping of firing pulses is process. The operating principle used in thislow due to the light engine load and this creates technology is that an electrical current flow in anhigh momentary accelerations and decelerations ionised gas is proportional to the flame electricalof the crankshaft. This causes speed variation conductivity. By placing a direct current bias acrosswhich can be mistakenly taken by the OBD sys- the spark plug electrodes, the conductivity can betem as a misfire. With this method of misfire measured (Figure 5.27). The spark current is useddetection, careful calibration of the OBD system to create this bias voltage and this eliminates theis necessary to avoid false detection. Another requirement for any additional voltage source.vehicle operation mode that can cause problems is The ion current is monitored and if no ion gen-operation of the vehicle on rough or poorly made erating flame is produced by the spark, no currentroads. This also causes rapid crankshaft oscilla- flows through the measurement circuit during thetion that could activate false triggers – under these working part of the cycle. The ion current vs. timeconditions the misfire detection must be disabled. trace is very different from that of a cycle when normal combustion occurs and this information can be used as a differentiator to detect misfireIonising current monitoring from normal combustion. This method has provenAn ionisation current sensing ignition system to be very effective at monitoring for misfiresconsists of one ignition coil per cylinder, normally under test conditions and also in practice. Spark Event – Spark Current Flow Measurement Period – Ion Current Flow BAT BAT Charged to – 80 volts Discharging 80 volts Spark D1 C1 Ion Flow D1 C1 R4 R4 D2 ION SIGNAL D2 ION SIGNAL R1 R1 ISIM components added ISIM components added to secondary circuit to secondary circuitFigure 5.26 Ion sensing circuit in direct ignition system Ion Current Waveforms Tek Stop: 50.0kS/s 8 Acqs Tek Stop: 50.0kS/s 16 Acqs Tek Stop: Single Seq 100kS/s T T T 3Ϫ T T T T 3Ϫ 3Ϫ 3ϩ Ch Ch Ch3 200m V -w Ch2 200mV-w M500ms 2.8 V 500m V *- M1.00m* 2.8 V 500m V*- M1.00ms 2.8 V Normal combustion Misfire in one cylinder KnockFigure 5.27 Resulting waveforms from the ion sensing system
  • 99. On-board diagnostics 83 The signal the system produces contains mis- Exhaust pressure analysisfire information and in addition, can provide This solution involves using a pressure sensor inobjective knock or detonation information. This exhaust manifold combined with a Fourier analy-can be used for engine control systems where sis as the first stage of the signal processing. Usingknowledge of the actual combustion process is a sensor to analyse the gas pulses in the exhaustrequired (as mentioned above). manifold, it is possible to detect single misfires. It is also possible to identify which cylinder isCylinder pressure sensing misfiring. This method is less intrusive than theThis technology has great potential not just for above and could potentially be retrofitted at theOBD applications but also for additional feedback production stage. A sensor in the exhaust canto the engine management system about the com- detect misfiring cylinders but cannot give use-bustion process due to the direct measurement ful, qualitative information about the combustiontechnique. This additional control dimension can process. This technique has been demonstrated asbe utilised to improve engine performance and capable of detecting all misfires at engine speedsreduce emissions further. With respect to misfire up to 6000 rpm, for all engine configurations,detection, this method provides reliable detection loads, and fuels. Generally, a ceramic capacitiveof a positive combustion event and can easily type sensor is been employed which has a shortdetect misfire with utmost reliability (Figure 5.28). response time and good durability. The major drawback is the availability ofsuitable sensors that could be installed into theengine at production and would be durable 5.4.9 Testing vehicles forenough to last the life of the engine and provide compliancethe required performance expected of sensors inan OBD system. For certain engine applications The manufacturer must demonstrate the correctsensors are available, and currently combustion function of the system to the appropriate authority.sensor technology is under rapid development For EOBD compliance this requires three com-such that this technical hurdle will soon be plete emission cycle runs (NEDC). This is knownovercome. as a demonstration test. A faulty component is installed or simulated which causes a violation of the emission limits; two preconditioning cycles are run and then one complete cycle to show that the error has been recorded and highlighted via illumination of the MIL. These phases are defined in EOBD legisla- tion as: ● simulation of malfunction of a component of the engine management or emission control system; ● preconditioning of the vehicle with a simu- lated malfunction; ● driving the vehicle with a simulated malfunc- tion over the type 1 test cycle (NEDC) and measuring the emissions of the vehicle; ● determining whether the OBD system reacts to the simulated malfunction and indicates malfunction in an appropriate manner to the vehicle driver. Typical failure modes induced to be detected are: ● Petrol/Gasoline Engines – Replacement of the catalyst with a deteri- orated or defective catalyst or electronicFigure 5.28 Cylinder pressure sensor mounted in the engine simulation of such a failure
  • 100. 84 Advanced automotive fault diagnosis – Engine misfire conditions according to the 5. Hold speed steady at cruise for 3 minutes. The conditions for misfire monitoring given in OBD system monitors EGR, secondary air – Replacement of the oxygen sensor with a system, oxygen sensors and EVAP system. deteriorated or defective oxygen sensor or 6. Overrun/coast down to low speed (i.e. 20 mph) electronic simulation of such a failure without using the brake or clutch. The OBD – Electrical disconnection of any other emis- systems check EGR and EVAP systems. sion-related component connected to a pow- 7. Accelerate back up to cruise for 5 minutes at ertrain management computer three quarter throttle. OBD checks misfire, – Electrical disconnection of the electronic fuel trim and EVAP. evaporative purge control device (if 8. Hold steady speed of cruise for 5 minutes. equipped). For this specific failure mode, OBD monitors catalytic converter efficiency, the type 1 test must not be performed misfire, fuel trim, oxygen sensors and EVAP systems.● Diesel Engines 9. Slow down to a stop without braking, OBD – Where fitted, replacement of the catalyst checks EGR and EVAP. with a deteriorated or defective catalyst or electronic simulation of this condition The system is now fully reset and ready for detec- – Where fitted, total removal of the particu- tion of new faults. The necessary drive cycle to late trap or, where sensors are an integral guarantee reset of the whole system is manufac- part of the trap, a defective trap assembly turer specific and should be checked appropriately. – Electrical disconnection of any fuelling system electronic fuel quantity and timing actuator Roadside test – Electrical disconnection of any other emis- An official in-service OBD2 emission test, as car- sion related component connected to a power- ried out in the USA by inspectors from the regu- train management computer latory authority, consists of the following three parts (a likely European development therefore).Conditioning Run After FaultRectification 1. Check MIL function at ignition switch on. 2. Plug in OBD scanner, check monitor readi-If an error has occurred with a component and ness. If monitors are not all showing as ready,this error has been recorded by the OBD system, the vehicle is rejected and further road testingthen (after the problem has been rectified) it is is to be done in order to activate all the readi-necessary to clear the fault code memory and test ness flags. At this stage the scanner will alsoor condition the vehicle to ensure that: download any fault codes that are present.● the fault has really been fixed and does not 3. An additional test, scanner command illumin- reoccur; ation of MIL via ECU to verify the correct● the system is set up ready for correct future function of the OBD system. detection of any faults.This can be done by putting the vehicle throughdrive cycle. A typical manufacturer defined drive 5.5 Summarycycle would consist of the following. Clearly OBD is here to stay – and be developed. It1. A cold start (coolant temperature less than should be seen as a useful tool for the technician 50°C, coolant and air temp within 11°C of as well as a key driver towards cleaner vehicles. each other). The creating of generic standards has helped2. Switch on ignition to allow oxygen sensor those of us at the ‘sharp end’ of diagnostics heating and diagnostics. significantly.3. Idle engine for 2 minutes with typical elect- OBD has a number of key emission related rical loads on (air conditioning and rear screen systems to ‘monitor’. It saves faults in these sys- heater). tems in a standard form that can be accessed4. Turn off loads and accelerate to cruise at using a scan tool. half throttle. The OBD system will check for In the final chapter of this book there is a short misfire, fuel trim and EVAP (canister purge) discussion on OBD3 and ways in which it may systems. be implemented in the future.
  • 101. On-board diagnostics 85Knowledge check questionsTo use these questions, you should first try to answer them without help but if necessary, refer back tothe content of the chapter. Use notes, lists and sketches to answer them. It is not necessary to writepages and pages of text!1. State the main reasons why OBD was developed.2. Explain what is meant by OBD monitors and list the most common.3. Describe how the P-codes are used to indicate faults.4. Explain with the aid of a sketch, how the ‘before and after cat’ lambda sensor signals are used by the OBD system to monitor catalyst operation.5. Explain what is meant by ‘healing of the fault memory’.
  • 102. 6Sensors and actuators6.1 Introduction Note: Any figures given are average or typical values. Refer to a good reference source suchSensors and actuators have a chapter all to as a workshop manual, or ‘Autodata’ for spe-themselves because they are so important! And cific values.also because the issues and diagnostic techniques Sensor and actuator waveforms are shownare common to many systems. For example, the in Chapter 7.testing procedure for an inductive engine speedsensor on a fuel injection system, is the same 6.2 Sensorsas for an inductive speed sensor on an ABSsystem. Testing sensors to diagnose faults is usually a 6.2.1 Thermistorsmatter of measuring their output signal. In some Thermistors are the most common device used forcases the sensor will produce this on its own (an temperature measurement on the motor vehicle.inductive sensor for example). In other cases, it The principle of measurement is that a changewill be necessary to supply the correct voltage in temperature will cause a change in resistanceto the device to make it work (Hall sensor for of the thermistor and hence an electrical signalexample). proportional to the temperature being measured. Figure 6.1 shows a typical thermistor used as an engine coolant temperature sensor. Note: It is normal to check that the vehicle cir- Most thermistors in common use are of the cuit is supplying the voltage before proceeding negative temperature coefficient (NTC) type. to test the sensor. The actual response of the thermistors can vary but typical values for those used on motor vehicles After the description of most sensors, and will vary from several k⍀ at 0°C to few hundredactuators a table is included listing the sensor, ⍀ at 100°C. The large change in resistance for aequipment necessary, test method(s), results of the small change in temperature makes the thermis-tests and a scope waveform. A waveform will be tor ideal for most vehicles uses. It can also be eas-reproduced where appropriate, as this is often the ily tested with simple equipment.recommended method of testing (see Chapter 4 Thermistors are constructed of semiconductorfor more details). The waveform shown will either materials. The change in resistance with a changebe the output of a sensor or the signal supplied to in temperature is due to the electrons being ablean actuator. to break free more easily at higher temperatures.Sensor Equipment Method(s) ResultsThermistor Ohmmeter Connect across the two terminals Most thermistors have a negative temperatureCoolant sensor or, if only one, from this to earth coefficient (NTC). This means the resistance falls asAir intake temperature temperature rises. A resistance check should give sensor readings broadly as follows:Ambient temperature 0°C ϭ 4500 ⍀ sensor 20°C ϭ 1200 ⍀etc. 100°C ϭ 200 ⍀6.2.2 Inductive sensors They work on the very basic principle of electricalInductive type sensors are used mostly for measur- induction (a changing magnetic flux will induceing the speed and position of a rotating component. an electromotive force in a winding). Figure 6.2
  • 103. Sensors and actuators 87Figure 6.1 Coolant temperature sensorshows a typical device used as a crankshaft speedand position sensor. The output voltage of most inductive type sen- Figure 6.2 Inductive crankshaft sensor and reluctor wheelsors approximates to a sine wave. The amplitude ofthis signal depends on the rate of change of flux. 6.2.3 Hall effect sensorsThis is determined mostly by the original design asin number of turns, magnet strength and the gap If a conductor is carrying a current in a transversebetween the sensor and the rotating component. magnetic field then a voltage will be produced atOnce in use though the output voltage increases right angles to the supply current. This voltage iswith the speed of rotation. In the majority of appli- proportional to the supply current and to the mag-cations, it is the frequency of the signal that is used. netic field strength.Sensor Equipment Method(s) ResultsInductive Ohmmeter A resistance test with the sensor Values vary from about 200 to 400 ⍀ on someCrankshaft speed disconnected vehicles to 800 to 1200 ⍀ on others.and positionABS wheel speed AC voltmeter AC voltage output with the engine The ‘sine wave’ output should be about 5 VCamshaft position cranking (less depending on engine speed) Many distributors employ Hall effect sensors. applications and a varying DC voltage for eitherThe output of this sensor is almost a square wave position sensing or current sensing.with constant amplitude. The Hall effect can also Hall effect sensors are being used in placebe used to detect current flowing in a cable, the of inductive sensors for applications such asmagnetic field produced round the cable being engine speed and wheel speed. The two mainproportional to the current flowing. advantages are that measurement of lower (or Hall effect sensors are becoming increasingly even zero) speed is possible and that the voltagepopular. This is partly due to their reliability but output of the sensors is independent of speed.also to the fact that they directly produce a constant Figure 6.3 shows a selection of Hall effectamplitude square wave in speed measurement distributor.Sensor Equipment Method(s) ResultsHall effect DC voltmeter The voltage output is measured as the This switches between 0 and aboutIgnition distributor engine or component is rotated slowly 8 V as the Hall chip is magnetised –Engine speed or notTransmission speed Logic probe The sensor is normally supplied with A logic probe will read high andWheel speed Do not use an 10 to 12 V low as the sensor output switchesCurrent flow in a wire ohmmeter as this(ammeter amp clamp) will damage the Hall chip
  • 104. 88 Advanced automotive fault diagnosis Figure 6.3 Hall effect distributor Figure 6.4 Optical sensor6.2.4 Optical sensors diode light source. If the light is focused to a very narrow beam then the output of the circuit shownAn optical sensor for rotational position is a rela- will be a square wave with frequency propor-tively simple device. The optical rotation sensor tional to speed.and circuit shown in Figure 6.4 consists of aphototransistor as a detector and a light emittingSensor Equipment Method(s) ResultsOptical DC voltmeter The device will normally be supplied with a Clear switching between low andIgnition distributor stabilised voltage. Check the output wire signal high voltageRotational speed as the device is rotated slowly6.2.5 Variable resistance the wiper contact will be proportional to throttleThe two best examples of vehicle applications position. In many cases now the throttle potentio-for variable resistance sensors are the throttle meter is used to indicate rate of change of throttleposition sensor and the flap type airflow sensor. position. This information is used when imple-Whereas variable capacitance sensors are used to menting acceleration enrichment or inversely overmeasure small changes, variable resistance sen- run fuel cut off. The output voltage of a rotarysors generally measure larger changes in pos- potentiometer is proportional to its position.ition. This is due to lack of sensitivity inherent in The airflow sensor shown as Figure 6.6 worksthe construction of the resistive track. on the principle of measuring the force exerted on The throttle position sensor as shown in Figure the flap by the air passing through it. A calibrated6.5 is a potentiometer in which, when supplied coil spring exerts a counter force on the flap suchwith a stable voltage, often 5 V, the voltage from that the movement of the flap is proportional to
  • 105. Sensors and actuators 89the volume of air passing through the sensor. To to this design. The resistive material used for thereduce the fluctuations caused by individual track is a ceramic metal mixture, which is burntinduction strokes a compensation flap is con- into a ceramic plate at very high temperature.nected to the sensor flap. The fluctuations there- The slider potentiometer is calibrated such thatfore affect both flaps and are cancelled out. Any the output voltage is proportional to the quantitydamage due to back firing is also minimised due of inducted air.Sensor Equipment Method(s) ResultsVariable resistance DC voltmeter This sensor is a variable resistor. If the The voltage should change smoothlyThrottle potentiometer supply is left connected then check the from about 0 to the supply voltageFlap type airflow sensor output on a DC voltmeter (often 5 V)Position sensor Ohmmeter With the supply disconnected, check Resistance should change smoothly the resistance 6.2.6 Manifold absolute pressure (MAP) sensor (strain gauges) When a strain gauge is stretched its resistance will increase and when it is compressed its resistance decreases. Most strain gauges consist of a thin layer of film that is fixed to a flexible backing sheet. This in turn is bonded to the part where strain is to be measured. Most resistance strain gauges have a resistance of about 100 ⍀. Strain gauges are often used indirectly to meas- ure engine manifold pressure. Figure 6.7 shows an arrangement of four strain gauges on a diaphragmFigure 6.5 Throttle potentiometer Bypass adjustment screw Measuring vane Rubber stopperAir outlet Air inlet Compensation vane Damping chamber Potentiometer Spiral spring Figure 6.6 Air flow meter (vane type)
  • 106. 90 Advanced automotive fault diagnosis ϩ ϫ Pressure Plates Diaphragm (a) (b) bends as pressure increases Plates y Changes dielectricFigure 6.7 Strain gauge pressure sensor distance (c)forming part of an aneroid chamber used to meas- Changes plate areaure pressure. When changes in manifold pressure Figure 6.8 Variable capacitance sensors (a) liquid level,act on the diaphragm the gauges detect the strain. (b) pressure, (c) positionThe output of the circuit is via a differential ampli-fier as shown, which must have a very high inputresistance so as not to affect the bridge balance. are compensated for by using four gauges whichThe actual size of this sensor may be only a few when affected in a similar way cancel out anymillimetres in diameter. Changes in temperature changes.Sensor Equipment Method(s) ResultsStrain gauges DC voltmeter The normal supply to an externally mounted The output should change between aboutMAP sensor MAP sensor is 5 V. Check the output as manifold 0 and 5 V as the manifold pressure changes –Torque stress pressure changes either by snapping the throttle as a general guide 2.5 V at idle speed open, road testing or using a vacuum pump on the sensor pipe6.2.7 Variable capacitance (b) Pressure sensor similar to the strain gauge pressure sensor but this time the distanceThe value of a capacitor is determined by: between capacitor plates changes.● surface area of its plates; (c) Position sensor detects changes in the area● distance between the plates; of the plates.● the dielectric (insulation between the plates). An interesting sensor used to monitor oil qual-Sensors can be constructed to take advantage of ity is now available. The type shown in Figure 6.9these properties. Three sensors each using the vari- works by monitoring changes in the dielectricable capacitance technique are shown in Figure 6.8. constant of the oil. This value increases as antiox-These are: idant additives in the oil deplete. The value rap- idly increases if coolant contaminates the oil. The(a) Liquid level sensor the change in liquid sensor output increases as the dielectric constant level changes the dielectric value. increases.Sensor Equipment Method(s) ResultsVariable DC voltmeter Measure the voltage at the sensor Small changes as the input to the sensor is varied – notecapacitance this is difficult to assess because of very low capacitance values
  • 107. Sensors and actuators 91 Figure 6.10 Knock sensor spring for the mass. Figure 6.10 shows a typical accelerometer or knock sensor in use on a spark ignition vehicle. The crystal is sandwiched between the body of the sensor and the seismic mass and is keptFigure 6.9 Bosch oil quality sensor under compression by the bolt. Acceleration forces acting on the seismic mass cause variations in the amount of crystal compression and hence gener-6.2.8 Knock sensors ate the piezo-electric voltage. The sensor, whenA piezo-electric accelerometer is a seismic mass used as an engine knock sensor, will also detectaccelerometer using a piezo-electric crystal to other engine vibrations. These are kept to a min-convert the force on the mass due to acceleration imum by only looking for ‘knock’ a few degreesinto an electrical output signal. The crystal not before and after top dead centre (TDC). Unwantedonly acts as the transducer but as the suspension signals are also filtered out electrically.Sensor Equipment Method(s) ResultsAccelerometer Scope Tap the engine block lightly Oscillating output that drops back to zero. If the whole systemKnock sensors (13 mm spanner) near the sensor is operating the engine will slow down if at idle speed6.2.9 Hot wire airflow sensor involved with the hot wire sensor is a voltageThe advantage of this sensor is that it measures air across a precision resistor. Figure 6.11 shows a hotmass flow. The basic principle is that as air passes wire air mass sensor.over a hot wire it tries to cool the wire down. If a The resistance of the hot wire and the preci-circuit is created such as to increase the current sion resistor are such that the current to heat thethrough the wire then this current will be propor- wire varies between 0.5 A and 1.2 A with differenttional to the airflow. A resistor is also incorporated air mass flow rates. High resistance resistors areto compensate for temperature variations. The ‘hot used in the other arm of the bridge and so currentwire’ is made of platinum and is only a few milli- flow is very small. The temperature compensat-metres long and about 70 ␮m thick. Because of ing resistor has a resistance of about 500 ⍀ whichits small size the time constant of the sensor is must remain constant other than by way of tem-very short, in fact in the order of a few millisec- perature change. A platinum film resistor is usedonds. This is a great advantage as any pulsations for these reasons. The compensation resistor canof the airflow will be detected and reacted to in a cause the system to react to temperature changescontrol unit accordingly. The output of the circuit within about three seconds.
  • 108. 92 Advanced automotive fault diagnosis The output of this device can change if the hot a thin film of nickel is used. The response timewire becomes dirty. Heating the wire to a very of this system is even shorter than the hot wire.high temperature for one second every time the Figure 6.12 shows a nickel film airflow sensor.engine is switched off prevents this by burning The advantage which makes a nickel thick-filmoff any contamination. In some air mass sensors thermistor ideal for inlet air temperature sensing isa variable resistor is provided to set idle mixture. its very short time constant. In other words its The nickel film airflow sensor is similar to the resistance varies very quickly with a change in airhot wire system. Instead of a hot platinum wire temperature.Sensor Equipment Method(s) ResultsHot wire DC voltmeter or This sensor includes electronic circuits to The output should change between about 0 and 5 VAir flow duty cycle meter condition the signal from the hot wire. as the air flow changes. 0.4 to 1 V at idle is typical. The normal supply is either 5 or 12 V. Or depending on the system in use the output Measure the output voltage as engine may be digital speed/load is varied6.2.10 Oxygen sensors The main active component of most types of oxygen sensors is zirconium dioxide (ZrO2). ThisThe vehicle application for an oxygen sensor is to ceramic is housed in gas permeable electrodes ofprovide a closed loop feedback system for engine platinum. A further ceramic coating is applied tomanagement control of the air fuel ratio. The the side of the sensor exposed to the exhaust gas asamount of oxygen sensed in the exhaust is directly a protection against residue from the combustionrelated to the mixture strength or air fuel ratio. The process. The principle of operation is that at tem-ideal air fuel ratio of 14.7:1 by mass is known as a peratures in excess of 300°C the zirconium dioxidelambda (␭) value of one. Exhaust gas oxygen will conduct the negative oxygen ions. The sensor(EGO) sensors are placed in the exhaust pipe near is designed to be responsive very close to a lambdato the manifold to ensure adequate heating. The value of one. As one electrode of the sensor is opensensors operate reliably at temperatures over to a reference value of atmospheric air a greater300°C. In some cases, a heating element is incor- quantity of oxygen ions will be present on thisporated to ensure that this temperature is reached side. Due to electrolytic action these ions permeatequickly. This type of sensor is known as a heated the electrode and migrate through the electrolyteexhaust gas oxygen sensor or HEGO for short! The (ZrO2). This builds up a charge rather like a bat-heating element (which consumes about 10 W) tery. The size of the charge is dependent on thedoes not operate all the time to ensure that the sen- oxygen percentage in the exhaust.sor does not exceed 850°C at which temperature The closely monitored closed loop feedbackdamage may occur to the sensor. This is why the of a system using lambda sensing allows verysensors are not fitted directly in the exhaust mani- accurate control of engine fuelling. Close controlfold. Figure 6.13 shows an EGO sensor in position. of emissions is therefore possible.Figure 6.11 Hot wire mass airflow sensor Figure 6.12 Hot film mass airflow sensor
  • 109. Sensors and actuators 93Sensor Equipment Method(s) ResultsOxygen DC voltmeter The lambda sensor produces its own A voltage of about 450 mV (0.45 V) is the normalLambda sensor voltage a bit like a battery. This can be figure produced at lambda value of one. The voltageEGO sensor measured with the sensor connected output, however, should vary smoothly betweenHEGO sensor to the system 0.2 and 0.8 V as the mixture is controlled by the ECULambdasonde6.2.11 Dynamic position sensors type of dynamic position sensor. Described as an accelerometer it is based on strain gauges.A dynamic position or movement of crash sensor There are two types of piezo-electric crystalcan take a number of forms; these can be described accelerometer, one much like an engine knockas mechanical or electronic. The mechanical system sensor and the other using spring elements. Aworks by a spring holding a roller in a set position severe change in speed of the vehicle will causeuntil an impact (acceleration/deceleration) above an output from these sensors as the seismic massa predetermined limit provides enough force to moves or the springs bend. See Section 6.2.8 onovercome the spring and the roller moves, triggering knock sensors for further details.a micro switch. The switch is normally open with aresistor in parallel to allow the system to be moni- Warningtored. Two switches similar to this may be used to For safety reasons, it is not recommended toensure that an air bag is deployed only in the case test a sensor associated with an air bag circuitof sufficient frontal impact. Figure 6.14 is a further without specialist knowledge and equipment.Sensor Equipment Method(s) ResultsAcceleration switch DC voltmeter Measure the supply and output as the sensor A clear switching between say 0 and 12 VDynamic position is subjected to the required acceleration6.2.12 Rain sensor light from an LED is reflected back from the outer surface of the glass. The amount of light reflectedRain sensors are used to switch on wipers auto- changes if the screen is wet, even with a few dropsmatically. Most work on the principle of reflected of rain. Figure 6.15 shows a typical rain sensor.light. The device is fitted inside the windscreen andSensor Equipment Method(s) ResultsRain! DC voltmeter Locate output wire – by trial and error if necessary and measure A clear switching between dry/wet output (splash water on the screen with the sensor correctly voltage levels fitted in position) Fixing points Sensing resistors Moving massFigure 6.13 Wide band lambda sensor (Source: Bosch Press) Figure 6.14 Strain gauges accelerometer
  • 110. 94 Advanced automotive fault diagnosis Figure 6.15 Rain sensor (Source: Bosch)6.3 Actuators6.3.1 IntroductionThere are many ways of providing control overvariables in and around the vehicle. ‘Actuators’ isa general term used here to describe a controlmechanism. When controlled electrically theywill either work by the thermal or magnetic effect.In this section the term actuator will be used tomean a device which converts electrical signalsinto mechanical movement.6.3.2 Testing actuatorsTesting actuators is simple as many are operatedby windings. The resistance can be measured withan ohmmeter. Injectors, for example, often have aresistance of about 16 ⍀. A good tip is that wherean actuator has more than one winding (steppermotor for example), the resistance of each shouldbe about the same. Even if the expected value isnot known, it is likely that if the windings all readthe same then the device is in order. With some actuators, it is possible to powerthem up from the vehicle battery. A fuel injector Figure 6.16 Fuel injectorshould click for example and a rotary air bypassdevice should rotate about half a turn. Be carefulwith this method as some actuators could be A good example of a solenoid actuator is a fueldamaged. At the very least use a fused supply injector. Figure 6.16 shows a typical example.( jumper) wire. When the windings are energised the armature is attracted due to magnetism and compresses the6.3.3 Solenoid actuators spring. In the case of a fuel injector, the movement is restricted to about 0.1 mm. The period that anThe basic operation of solenoid actuators is very injector remains open is very small; under varioussimple. The term ‘solenoid’ means: ‘many coils operating conditions between 1.5 and 10 ms isof wire wound onto a hollow tube’. This is often typical. The time it takes an injector to open andmisused but has become so entrenched that terms close is also critical for accurate fuel metering.like ‘starter solenoid’, when really it is a starter Some systems use ballast resistors in series withrelay, are in common use. the fuel injectors. This allows lower inductance
  • 111. Sensors and actuators 95and resistance operating windings to be used, thus 6.3.4 Motorised and solenoidspeeding up reaction time. actuators Other types of solenoid actuators, for exampledoor lock actuators, have less critical reaction times. Permanent magnet electric motors are used in manyHowever, the basic principle remains the same. applications and are very versatile. The output of aActuator Equipment Method(s) ResultsSolenoid Ohmmeter Disconnect the component and The resistance of commonly used injectors is about 16 ⍀Fuel injector measure its resistance Lock and other actuators may have two windingsLock actuator (e.g. lock and unlock). The resistance values are very likely to be the samemotor is of course rotation, and this can be used in in Figure 6.17. They are used as window liftmany ways. If the motor drives a rotating ‘nut’ motors. Some of these use Hall effect sensors orthrough which a plunger is fitted on which there is an extra brush as a feedback device.a screw thread, the rotary action can easily be con- A rotary idle actuator is a type of motor actu-verted to linear movement. In most vehicle appli- ator. This device is used to control idle speed bycations the output of the motor has to be geared controlling air bypass. There are two basic typesdown, this is to reduce speed and increase torque. in common use. These are single winding types,Permanent magnet motors are almost universally which have two terminals, and double windingused now in place of older and less practical types, which have three terminals. Under ECUmotors with field windings. Some typical exam- control the motor is caused to open and close aples of the use of these motors are listed as follows: shutter controlling air bypass. These actuators● windscreen wipers; only rotate about 90° to open and close the valve.● windscreen washers; As these are permanent magnet motors the ‘sin-● headlight lift; gle or double windings’ refers to the armature.● electric windows; The single winding type is fed with a square● electric sun roof; wave signal causing it to open against a spring● electric aerial operation; and then close again, under spring tension. The● seat adjustment; on/off ratio or duty cycle of the square wave will● mirror adjustment; determine the average valve open time and hence● headlight washers; idle speed.● headlight wipers; With the double winding type the same square● fuel pumps; wave signal is sent to one winding but the inverse● ventilation fans. signal is sent to the other. As the windings are wound in opposition to each other if the duty One disadvantage of simple motor actuators is cycle is 50% then no movement will take place.that no direct feedback of position is possible. Altering the ratio will now cause the shutter toThis is not required in many applications; how- move in one direction or the other.ever, in cases such as seat adjustment when a A further type is an on/off solenoid where a‘memory’ of the position may be needed, a vari- port is opened or closed as the solenoid is oper-able resistor type sensor can be fitted to provide ated. This type is shown in Figure 6.18.feedback. Two typical motor actuators are shownActuator Equipment Method(s) ResultsMotor Battery supply (fused) Most ‘motor’ type actuators can be Normal operation with current drawSee previous list run from a battery supply after they appropriate to the ‘work’ done by the device. Ammeter are disconnected from the circuit. For example, a fuel pump motor may draw up If necessary the current draw to 10 A, but an idle actuator will only draw can be measured 1 or 2 AActuator Equipment Method(s) ResultsSolenoid actuator Duty cycle meter Most types are supplied with a variable The duty cycle will vary as a change is required(idle speed control) ratio square wave
  • 112. 96 Advanced automotive fault diagnosisFigure 6.17 Window lift motor and wiper motors6.3.5 Stepper motorsStepper motors are becoming increasingly popu-lar as actuators in the motor vehicle. This is Figure 6.18 Solenoid idle actuatormainly because of the ease with which they can 1be controlled by electronic systems. 4Ј 2 Stepper motors fall into three distinct groups, thebasic principles of which are shown in Figure 6.19. Variable 3Ј 3 reluctance● variable reluctance motors;● permanent magnet (PM) motors;● hybrid motors. 2Ј 4The underlying principle is the same for each 1Јtype. All of them have been and are being used invarious vehicle applications. Rotor The basic design for a PM stepper motor com-prises two double stators. The rotor is often made Permanent magnetof barium-ferrite in the form of a sintered annularmagnet. As the windings are energised in onedirection then the other the motor will rotate in90° steps. Half step can be achieved by switching Rotor Windingson two windings. This will cause the rotor to lineup with the two stator poles and implement a halfstep of 45°. The direction of rotation is determinedby the order in which the windings are switched Hybridon or off or reversed. The main advantages of a stepper motor arethat feedback of position is not required. This isbecause the motor can be indexed to a knownstarting point and then a calculated number of Figure 6.19 Basic principle of variable reluctance permanentsteps will move the motor to any suitable position. magnet and hybrid stepper motorActuator Equipment Method(s) ResultsStepper motor Ohmmeter Test the resistance of each winding with Winding resistances should be the same.Idle speed air bypass the motor disconnected from the Values in the region of 10 to 20 ⍀ areCarburettor choke control circuit typicalSpeedometer drivers6.3.6 Thermal actuators gauge needle. A further example is an auxiliaryAn example of a thermal actuator is the move- air device used on many earlier fuel injectionment of a traditional type fuel or temperature systems. The principle of the gauge is shown in
  • 113. Sensors and actuators 97 Heater windingFixedpoint Bimetal stripFigure 6.20 Thermal actuator principleFigure 6.20. When current is supplied to the ter-minals, a heating element operates and causes a Figure 6.21 Rotary valve EGR–Delphibimetallic strip to bend, which moves the pointer. The main advantage of this type of actuator, of its surroundings. This is ideal for applicationswhen used as an auxiliary device, apart from its such as fast idle or cold starting control where,simplicity, is that if it is placed in a suitable posi- once the engine is hot, no action is required fromtion its reaction time will vary with the temperature the actuator.Actuator Equipment Method(s) ResultsThermal Ohmmeter Check the winding for continuity. If OK Continuity and slow movementAuxiliary air device Fused battery supply power up the device and note its operation (several seconds to a few minutes) toInstrument display (for instruments, power these but use a close the valve or move as required resistor in place of the sender unit)6.3.7 Exhaust gas recirculation gas recirculation (EEGR) valve for use in diesel(EGR) valve engine applications (Lucas Varity). This device is shown in Figure 6.21. It has a self-cleaningVarious types of EGR valve are in use based on action, accurate gas flow control and a fast reac-simple solenoid operation. One development in tion speed. The waveform shown in the table isactuator technology is the rotary electric exhaust not necessarily from this type of valve.Actuator Equipment Method(s) ResultsEGR valve Ohmmeter Check the winding(s) for continuity. If OK power up Continuity and rapid movement to Fused battery supply the device and note its operation close the valve Knowledge check questions To use these questions, you should first try to answer them without help but if necessary, refer back to the content of the chapter. Use notes, lists and sketches to answer them. It is not necessary to write pages and pages of text! 1. Explain how a knock sensor operates and why it is used. 2. Describe how to test the operation of a Hall sensor using multimeter. 3. List in a logical sequence, how to diagnose a fault with one fuel injector on a V6 multipoint system. 4. Outline two methods of testing the operation of a sensor that uses a variable resistor (throttle pot or vane type airflow sensors for example). 5. Explain with the aid of a sketch, what is meant by ‘duty cycle’ in connection with an idle speed con- trol valve.
  • 114. 7Engine systems7.1 Introduction When the term ‘stroke’ is used it means the move- ment of a piston from top dead centre (TDC) toThe main sections in this chapter that relate to an bottom dead centre (BDC) or the other way round.area of the vehicle start with an explanation of The following table explains the spark ignitionthe particular system. The sections then conclude (SI) and compression ignition (CI) four strokewith appropriate diagnostic techniques and symp- cycles – for revision purposes! Figure 7.2 showstom charts. Extra tests and methods are explained the SI cycle.where necessary. Stroke Spark ignition Compression ignition Induction The fuel air mixture is Air is forced into the7.2 Engine operation forced into the cylinder cylinder through the through the open inlet open inlet valve valve because as the because as the piston7.2.1 Four stroke cycle piston moves down it moves down it makes makes a lower pressure. a lower pressure. It isFigure 7.1 shows a modern vehicle engine. Engines It is acceptable to say acceptable to say thelike this can seem very complex at first but keep in the mixture is drawn air is drawn into themind when carrying out diagnostic work that, with into the cylinder cylindervery few exceptions, all engines operate on the Compression As the piston moves As the piston movesfour stroke principle. The complexity is in the sys- back up the cylinder back up the cylindertems around the engine to make it operate to its the fuel air mixture is the fuel air mixture ismaximum efficiency or best performance. With compressed to about compressed in some an eighth of its original engines to about athis in mind then, back to basics! volume because the sixteenth of its The engine components are combined to use inlet and exhaust valves original volumethe power of expanding gas to drive the engine. are closed. This is a because the inlet and Figure 7.1 The BMW 2.8 litre six cylinder engine uses variable camshaft control
  • 115. Engine systems 99Figure 7.2 Four stroke cycle compression ratio of exhaust valves are in their standard family cars. Larger cars do, how- 8:1, which is typical for closed. This is a ever, make use of the ‘Vee’ configuration. The many normal engines compression ratio of 16:1, which causes a opposed layout whilst still used is less popular. large build up of heat Engine firing order is important. This means thePower At a suitable time At a suitable time order in which the power strokes occur. The fig- before top dead centre, before top dead centre, ures above have the cylinders numbered, and a spark at the plug very high pressure listed by each are some common firing orders. It ignites the compressed atomised diesel fuel is is important to check in the workshop manual or mixture. The mixture injected into the data book when working on a particular engine. now burns very quickly combustion chamber. and the powerful The mixture burns very expansion pushes the quickly and the piston back down the powerful expansion 7.2.3 Camshaft drives cylinder. Both valves pushes the piston back are closed down the cylinder. The engine drives the camshaft in one of three The valves are closed ways, gear drive, chain drive or by a drive belt.Exhaust The final stroke occurs The final stroke occurs The last of these is now the most popular as it as the piston moves as the piston moves back tends to be simpler and quieter. Note in all cases back up the cylinder up the cylinder and that the cam is driven at half the engine speed. and pushes the spent pushes the spent gases This is done by the ratio of teeth between the gases out of the now out of the now open crank and cam cogs which is 1:2, for example 20 open exhaust valve exhaust valve crank teeth and 40 cam teeth. ● Camshaft drive gears Gears are not used7.2.2 Cylinder layouts very often on petrol engines but are used onGreat improvements can be made to the perform- larger diesel engines. They ensure a good pos-ance and balance of an engine by using more than itive drive from the crankshaft gear to theone cylinder. Once this is agreed the actual layout camshaft.of the cylinders must be considered. The layout ● Camshaft chain drive Chain drive is stillcan be one of three possibilities as follows. used but was even more popular a few years ago. The problems with it are that a way must● In-line or straight The cylinders are in a be found to tension the chain and also provide straight line. They can be vertical, inclined or lubrication. horizontal. ● Camshaft drive belt Camshaft drive belts● Vee The cylinders are in two rows at a set have become very popular. The main reasons angle. The actual angle varies but is often 60° for this are that they are quieter, do not need or 90°. lubrication and are less complicated. They do● Opposed The cylinders are in two rows break now and then but this is usually due to opposing each other and are usually horizontal. lack of servicing. Cam belts should be renewed By far the most common arrangement is the at set intervals. Figure 7.3 shows an examplestraight four and this is used by all manufacturers of the data available relating to camshaft drive
  • 116. 100 Advanced automotive fault diagnosis belt fitting. This is one of the many areas will be noisy. If the clearance is too small the valves where data is essential for diagnostic checks. will not close and no compression will be possible. When an engine is running the valves become very hot and therefore expand. The exhaust valve clear-7.2.4 Valve mechanisms ance is usually larger than the inlet, because it getsA number of methods are used to operate the hotter. Regular servicing is vital for all componentsvalves. Three common types are shown as Figure but, in particular, the valve operating mechanism7.4 and a basic explanation of each follows. needs a good supply of clean oil at all times.● Overhead valve with push rods and rockers The method has been used for many years and although it is not used as much now, many vehicles still on the road are described as overhead valve (OHV). As the cam turns it moves the follower, which in turn pushes the push rod. The push rod moves the rocker, which pivots on the rocker shaft and pushes the valve open. As the cam moves further it allows the spring to close the valve.● Overhead cam with followers Using an overhead cam (OHC) reduces the number of moving parts. In the system shown here the lobe of the cam acts directly on the follower which pivots on its adjuster and pushes the valve open.● Overhead cam, direct acting and automatic adjusters Most new engines now use an OHC with automatic adjustment. This saves on repair and service time and keeps the cost to the cus- tomer lower. Systems vary between manufac- turers, some use followers and some have the cam acting directly on to the valve. In each case though the adjustment is by oil pressure. A type of plunger, which has a chamber where oil can be pumped under pressure, operates the valve. This expands the plunger and takes up any unwanted clearance. Valve clearance adjustment is very important.If it is too large the valves will not open fully and Figure 7.3 Timing belt data is essential Figure 7.4 Valve operating mechanisms
  • 117. Engine systems 1017.2.5 Valve and ignition timing 7.3 Diagnostics – enginesValve timing is important. The diagram of Figure7.5 shows accurately the degrees of rotation of 7.3.1 Systematic testing examplethe crankshaft where the inlet and exhaust valves If the reported fault is excessive use of engine oilopen and close during the four stroke cycle. The proceed as follows.actual position in the cycle of operation whenvalves open and close depends on many factors 1. Question the customer to find out how muchand will vary slightly with different designs of oil is being used.engine. Some cars now control valve timing by 2. Examine the vehicle for oil leaks and blueelectronics. The diagram is marked to show what smoke from the exhaust.is meant by valve lead, lag and overlap. Ignition 3. For example, oil may be leaking from a gaskettiming is marked on the diagram. Note how this or seal – if no leaks are found the engine maychanges as engine speed changes. be burning the oil. The valve timing diagram shows that the valves 4. A compression test, if the results were accept-of a four stroke engine open just before and close able, would indicate a leak to be the most likelyjust after the particular stroke. Looking at the tim- fault. Clean down the engine and run for aing diagram, if you start at position IVO, the piston while, the leak might show up.is nearly at the top of the exhaust stroke when the 5. For example change the gasket or seals.inlet valve opens (IVO). The piston reaches the top 6. Run a thorough inspection of vehicle systems,and then moves down on the intake stroke. Just particularly those associated with the engine.after starting the compression stroke the inlet valve Double check that the fault has been recti-closes (IVC). The piston continues upwards and, at fied and that you have not caused any othera point several degrees before top dead centre, the problems.spark occurs and starts the mixture burning. The maximum expansion is ‘timed’ to occur 7.3.2 Test equipmentafter top dead centre, therefore the piston is pusheddown on its power stroke. Before the end of this Note: You should always refer to the manufac-stroke the exhaust valve opens (EVO). Most of turer’s instructions appropriate to the equipmentthe exhaust gases now leave because of their very you are using.high pressure. The piston pushes the rest of the Compression testerspent gases out as it moves back up the cylinder.The exhaust valve closes (EVC) just after the end With this device the spark plugs are removed andof this stroke and the inlet has already opened, the tester screwed or held in to each spark plugready to start the cycle once again. hole in turn. The engine is cranked over by the The reason for the valves opening and closing starter and the gauge will read the compressionlike this is that it makes the engine more efficient or pressure of each cylinder.by giving more time for the mixture to enter and Cylinder leakage testerthe spent gases to leave. The outgoing exhaustgases in fact help to draw in the fuel air mixture A leakage tester uses compressed air to pressurisefrom the inlet. Overall this makes the engine have each cylinder in turn by a fitting to the spark pluga better ‘volumetric efficiency’. hole. The cylinder under test is set to TDC com- pression. The percentage of air leaking out and where it is leaking from helps you determine the engine condition. For example if air is leaking through the exhaust pipe then the exhaust valves are not sealing. If air leaks into the cooling system then a leak from the cylinder to the water jacket may be the problem (blown head gasket is possible). Figure 7.6 shows a selection of snap-on diagnostic gauges – vacuum, compression and leakage. 7.3.3 Test results Some of the information you may have to getFigure 7.5 Valve and ignition timing from other sources such as data books, or a
  • 118. 102 Advanced automotive fault diagnosisworkshop manual is listed in the following table. check the oil pressure Incorrect valve Adjust clearances toTest carried out Information required clearances or correct settings or defective automatic replace defectiveCompression test Expected readings for the particular adjuster adjuster engine under test. For example the Piston slap on side Engine overhaul pressure reach for each cylinder may of cylinder required now or be expected to read 800 kPa Ϯ 15% quite soonCylinder leakage test The percentage leak that is allowed Vibration Engine mountings Secure or renew for the tester you are using; some loose or worn allow about 15% leakage as the limit Misfiring Check engine ancillary systems such as fuel and7.3.4 Engine fault diagnosis ignitiontable 1Symptom Possible causes Suggested action 7.3.5 Engine fault diagnosis or faults table 2Oil consumption Worn piston rings Engine overhaul Please note that this section covers related engine and/or cylinders systems as well as the engine itself. Worn valve stems, Replace valves guides or stem oil (guides if possible) seals and oil seals Symptom Possible causeOil on engine Leaking gaskets or Replace appropriate Engine does not rotate Battery connection loose oror floor seals gasket or seal when trying to start corroded Build up of pressure Check engine Battery discharged or faulty in the crankcase breather system Broken loose or disconnectedMechanical Worn engine Replace bearings or wiring in the starter circuitknocking noises bearings (big ends or overhaul engine. Defective starter switch or automatic mains for example) Good idea to also gearbox inhibitor switchFigure 7.6 Diagnostic gauges
  • 119. Engine systems 103 Starter pinion or flywheel ring gear Incorrect plugs or plug gaps loose HT leads breaking down Earth strap broken. Loose or Engine stalls Idle speed incorrect corroded CO setting incorrectEngine rotates but No fuel in the tank! Fuel filter blockeddoes not start Discharged battery (slow rotation) Air filter blocked Battery terminals loose or corroded Intake air leak Air filter dirty or blocked Idle control system not working Low cylinder compressions Lack of power Fuel filter blocked Broken timing belt Air filter blocked Damp ignition components Ignition timing incorrect Fuel system fault Low fuel pump delivery Spark plugs worn to excess Uneven or low cylinder Ignition system open circuit compressions (maybe valves)Difficult to start when Discharged battery (slow rotation) Fuel injectors blockedcold Battery terminals loose or corroded Brakes binding or clutch slipping Air filter dirty or blocked Backfires Incorrect ignition timing Low cylinder compressions Incorrect valve timing (cam belt not Fuel system fault fitted correctly) Spark plugs worn to excess Fuel system fault (airflow sensor on Enrichment device not working some cars) (choke or injection circuit) Oil pressure gauge low Low engine oil levelDifficult to start when Discharged battery (slow rotation) or warning light on Faulty sensor or switchhot Battery terminals loose or corroded Worn engine oil pump and/or engine Air filter dirty or blocked bearings Low cylinder compressions Engine overheating Fuel system fault Oil pickup filter blockedStarter noisy Starter pinion or flywheel ring gear Pressure relief valve not working loose Runs on when Ignition timing incorrect Starter mounting bolts loose switched off Idle speed too high Starter worn (bearings, etc.) Anti-run on device not working Discharged battery (starter may Carbon build up in engine jump in and out) Engine overheatingStarter turns engine Discharged battery (slow rotation) Pinking or knocking Ignition timing incorrectslowly Battery terminals loose or corroded under load Ignition system fault Earth strap or starter supply loose Carbon build up in engine or disconnected Knock sensor not working Internal starter fault Sucking or whistling Leaking exhaust manifold gasketEngine starts but then Ignition wiring connection noises Leaking inlet manifold gasketstops immediately intermittent Cylinder head gasket Fuel system contamination Inlet air leak Fuel pump or circuit fault (relay) Water pump or alternator Intake system air leak bearing Ballast resistor open circuit (older cars) Rattling or tapping Incorrect valve clearances Worn valve gear or camshaftErratic idle Air filter blocked Loose component Incorrect plug gaps Inlet system air leak Thumping or knocking Worn main bearings (deep Incorrect CO setting noises knocking/rumbling noise) Uneven or low cylinder Worn big end bearings (heavy compressions (maybe valves) knocking noise under load) Fuel injector fault Piston slap (worse when cold) Incorrect ignition timing Loose component Incorrect valve timing Rumbling noises Bearings on ancillary componentMisfire at idle speed Ignition coil or distributor cap tracking Poor cylinder compressions Engine breather blocked 7.4 Fuel system Inlet system air leak Faulty plugs Authors Note: Even though carburettor fuel systemsMisfire through all Fuel filter blocked are now very rare, they are still used on some specialistspeeds Fuel pump delivery low vehicles. For this reason, and because it serves as a Fuel tank ventilation system blocked good introduction to fuel systems, I decided to include Poor cylinder compressions this section.
  • 120. 104 Advanced automotive fault diagnosis7.4.1 Introduction 7.4.2 CarburationAll vehicle fuel systems consist of the carburettor Figure 7.7 shows a simple fixed choke carburet-or fuel injectors, the fuel tank, the fuel pump, and tor operating under various conditions. The floatthe fuel filter, together with connecting pipes. An and needle valve assembly ensures a constantengine works by the massive expansion of an level of petrol in the float chamber. The venturiignited fuel air mixture acting on a piston. The job causes an increase in air speed and hence a dropof the fuel system is to produce this mixture at just in pressure in the area of the outlet. The main jetthe right ratio to run the engine under all operat- regulates how much fuel can be forced into thising conditions. There are three main ways this is intake air stream by the higher pressure now appar-achieved: ent in the float chamber. The basic principle is that as more air is forced into the engine then more● petrol is mixed with air in a carburettor; fuel will be mixed in to the air stream.● petrol is injected into the manifold, throttle The problem with this system is that the amount body cylinder or to mix with the air; of fuel forced into the air stream does not linearly● diesel is injected under very high pressure follow the increase in air quantity, unless further directly into the air already in the engine com- compensation fuel and air jets are used. A vari- bustion chamber. able venturi carburettor, which keeps the air pres-This section will only examine the carburettor sure in the venturi constant but uses a taperedsystems; diesel and injection comes under engine needle to control the amount of fuel, is anothermanagement later. method used to control fuel air ratio. Choke flap Air-correction Air vent Idling jet jetThrottlevalvenearlyclosed Emulsion tube High vacuum Progression High vacuum moves in this area drilling to main outlet On idling, high vacuum below the throttle Fuel is drawn from the main outlet as the vacuum valve draws fuel through a separate circuit around it increasesChoke flap Choke flap Pump outlet Accelerator pump Throttle Throttle valve valve Accelerator linkage A flap is used to partially block the barrel for The accelerator pump squirts an enriching shot of fuel cold starts. It increases vacuum around the down the barrel to provide rapid response when the fuel outlet and draws more fuel to provide a throttle is opened quickly, when extra power is needed rich mixtureFigure 7.7 A simple fixed choke carburettor
  • 121. Engine systems 1057.4.3 Stages of carburation stages to consider. This can help a lot with diag- nosing faults because it helps you ‘zoom in’ onThe basic principle of a carburettor is to mix fuel the area where the problem is likely to be found.and air together in the correct ratios dependent Although the examples given relate to a standardon engine loads and temperature. Fuel flow is fixed choke carburettor, the stages are still rele-caused by the low air pressure around a spray vant to all other types. The six stages along withoutlet and atmospheric pressure acting on the problems and possible solutions are listedfuel in the float chamber. below. Whilst the engine’s requirement for air fuel mix-ture is infinitely variable, there are six discernibleStage Query or problem Possible solution or symptomsCold starting when a richer What would be the result of the choke not Difficult starting due to a weak mixturemixture is required to reduce the closing fully when starting a cold engine?effects of condensation within the When starting a cold engine with full choke To decrease the depression below theinlet manifold and to aid combustion why must the choke valve partially open choke valve thus preventing the mixture when the engine is running? from becoming too richIdle when the minimum amount of A customer complains of erratic idling and Idling fuel jet restrictedfuel should be provided to ensure hesitation when moving off from rest? Mixture strength too weak at idlecomplete combustion and efficiency What would be the result of exchanging the Weak idling air to fuel mixture idle fuel jet for one of a smaller size? Erratic idle and flat spots when accelerating from stationaryProgression when a smooth What is the purpose of the progression Ensures an even changeover to the mainsequence of change is necessary drilling? systemfrom a range of drillings. This is What would be the result of the progression Lack of response during initial accelerationnormally from idle until the main drillings becoming restricted? with warm enginejets come into playAcceleration when a measured What function does the accelerator pump Enriches the mixture for hard accelerationincrease in the supply of fuel is perform?required to sustain an initial burst The customer complains of a flat spot during Faulty non-return valve in the pump circuitof speed hard acceleration when engine is hot? Accelerator pump diaphragm holedCruising where the need is for What complaint would the customer have if Poor mid throttle range performancemetered fuel to maintain speed at the main air correction jet was restricted? combined with high fuel consumptionthe most efficient setting If mixture was too weak on cruise, what Possible misfiring and poor performance would be the effect on operation? Flat spots on accelerationHigh speeds where a slightly richer What operating symptoms could be caused Reduced top speedmixture is required to maintain by blocked full load enrichment tube?efficient combustion and to avoid What symptoms would be observed if the Possible poor fuel consumption anddamage to the engine mixture was too rich at high speed? reduced engine performance7.4.4 Electronic control of Choke A rotary choke or some other form of valve or flap operates the choke mechanismcarburation depending on engine and ambient temperature conditionsElectronic control of a carburettor is made in the Overrun A small solenoid operated valve or similarfollowing areas. fuel cut off cuts off the fuel under particular conditions. These conditions are often that the engineIdle speed Controlled by a stepper motor to prevent temperature must be above a set level, engine stalling but still allow a very low idle speed to speed above a set level and the accelerator improve economy and reduce emissions. Idle pedal is in the off position speed may also be changed in response to a signal from an automatic gearbox to prevent either the engine from stalling or the car from The air fuel ratio is set by the mechanical design trying to creep of the carburettor, so it is very difficult to controlFast idle The same stepper motor as above controls fast idle in response to a signal from the by electrical means. Some systems have used engine temperature sensor during the warm electronic control of, say, a needle and jet but this up period has not proved to be very popular.
  • 122. 106 Advanced automotive fault diagnosis Figure 7.8 shows the main components of the on switching off the ignition. When the ignition issystem used on some vehicles. As with any con- next turned on the stepper will drive the idle andtrol system it can be represented as a series of choke mechanism by a certain number of stepsinputs, a form of control and a number of out- determined as at the end of the last paragraph.puts. The inputs to this system are as follows. The other main output is the overrun fuel cut off solenoid. This controls the air pressure in theEngine speed From a signal wire to the negative side of the float chamber and when operated causes pres- ignition coil as is common with many systems sure in the float chamber and pressure in the ven-Engine This is taken from a thermistor located in the turi at the jet outlet to equalise. This prevents anycoolant cylinder head waterways. The same sensor is fuel from being ‘drawn’ into the air stream.temperature used for the programmed ignition system if fittedAmbient A thermistor sensor is placed such as totemperature register the air temperature. A typical position is at the rear of a headlight 7.5 Diagnostics – fuelThrottle This switch is placed under the actual pedal systemswitch and only operates when the pedal is fully off, that is when the butterfly valve in the carburettor is closed 7.5.1 Systematic testing example If the reported fault is excessive fuel consump- The main controlling actuator of this system is tion proceed as follows.the stepper motor. This motor controls by reduc-tion gears a rotary choke valve for cold starting 1. Check that the consumption is excessive for theconditions. The same stepper motor controls idle particular vehicle. Test it yourself if necessary.and fast idle with a rod that works on a snail type 2. Are there any other problems with the vehicle,cam. The system can operate this way because the misfiring for example or difficult starting?first part of the movement of the stepper motor does 3. For example if the vehicle is misfiring as wellnot affect the choke valve; it only affects the idle this may indicate that an ignition fault is thespeed by opening the throttle butterfly slightly. cause of the problem.Further rotation then puts on the choke. The extent, 4. Remove and examine spark plugs, check HTto which the choke is on is determined from engine lead resistance and ignition timing. Check COtemperature and ambient temperature. emissions. The ECU ‘knows’ the position of the stepper 5. Renew plugs and set fuel mixture.motor before setting the choke position by a 6. Road test vehicle for correct engine operation.process known as indexing. This involves thestepper motor being driven to say its least setting 7.5.2 Test equipment Note: You should always refer to the manufac- turer’s instructions appropriate to the equip- ment you are using. Exhaust gas analyser (Figure 7.9) This is a sophisticated piece of test equipment used to measure the make up of the vehicle’s exhaust gas. The most common requirement is the measuring of carbon monoxide (CO). A sam- ple probe is placed in the exhaust tail pipe or a special position before the catalytic converter if fitted, and the machine reads out the percentage of certain gases produced. A digital readout is most common. The fuel mixture can then be adjusted until the required readings are obtained. Fuel pressure gauge The output pressure of the fuel pump can be tested to ensure adequate delivery. The device isFigure 7.8 HIF variable venturi carburettor with electronic a simple pressure gauge but note the added pre-control components cautions necessary when dealing with petrol.
  • 123. Engine systems 107Figure 7.9 Exhaust gas analyser7.5.3 Test results Defective fuel pump Renew/check it is being drivenSome of the information you may have to get No electrical supply Check fuses/tracefrom other sources such as data books or a work- to pump faultshop manual is listed in the following table. Engine will not or Choke or enrichment Check linkages is difficult to start device not working or automatic actuatorTest carried out Information required Engine stalls or Idle speed incorrectly Look up correct will not idle set settings and adjustExhaust gas analysis CO setting. Most modern vehicles smoothly Mixture setting Look up correct will have settings of about 1% or less. wrong settings and adjust If a ‘cat’ is fitted then the readings will Ignition problem Check ignition be even lower when measured at the system tail pipe Poor acceleration Blockage in Strip down andFuel pressure The expected pressure readings will carburettor clean out or try a vary depending on the type of fuel accelerator pump carburettor cleaner system. Fuel injection pressure will be first about 2.5 bar whereas fuel pressure Partially blocked filter Renew for a carburettor will be about 0.3 bar Injection electrical Refer to specialistFuel delivery How much fuel the pump should fault information move in a set time. This will again vary Excessive fuel Incorrect mixture Look up correct with the type of fuel system. I litre in consumption settings settings and 30 seconds is typical for some adjust injection fuel pumps Driving technique! Explain to the customer – but be diplomatic!7.5.4 Fuel fault diagnosis table 1 Black smoke from Excessively rich Look up correct exhaust mixture settings and adjustSymptom Possible faults Suggested action Flooding Check and adjust carburettor floatNo fuel at Empty tank! Fill it! settings andcarburettor or Blocked filter or line Replace filter, operationinjection fuel rail renew/repair line
  • 124. 108 Advanced automotive fault diagnosis7.5.5 Fuel fault diagnosis table 2 approximately 8 kV is required. For higher com- pression ratios and weaker mixtures, a voltage upSymptom Possible cause to 20 kV may be necessary. The ignition system has to transform the normal battery voltage ofExcessive consumption Blocked air filter 12 V to approximately 8 to 20 kV and, in addition, Incorrect CO adjustment Fuel injectors leaking has to deliver this high voltage to the right cylin- Ignition timing incorrect der, at the right time. Some ignition systems will Temperature sensor fault supply up to 40 kV to the spark plugs. Load sensor fault Conventional ignition is the forerunner of the Low tyre pressures more advanced systems controlled by electron- Driving style! ics. However, the fundamental operation of mostFuel leakage Damaged pipes or unions Fuel tank damaged ignition systems is very similar; one winding of a Tank breathers blocked coil is switched on and off causing a high voltageFuel smell Fuel leak to be induced in a second winding. A coil igni- Breather incorrectly fitted tion system is composed of various components Fuel cap loose and sub-assemblies; the actual design and con- Engine flooding struction of these depend mainly on the engineIncorrect emissions Incorrect adjustments with which the system is to be used. Fuel system fault Air leak into inlet Blocked fuel filter Blocked air filter 7.7.2 Advance angle (timing) Ignition system fault For optimum efficiency the ignition advance angle should be such as to cause the maximum combustion pressure to occur about 10° after7.6 Introduction to engine TDC. The ideal ignition timing is dependent onmanagement two main factors, engine speed and engine load. An increase in engine speed requires the ignitionEngine management is a general term that timing to be advanced. The cylinder charge, ofdescribes the control of engine operation. This can air fuel mixture, requires a certain time to burnrange from a simple carburettor to control or man- (normally about 2 ms). At higher engine speedsage the fuel, with an ignition distributor with con- the time taken for the piston to travel the sametact breakers to control the ignition to a very distance reduces. Advancing the time of the sparksophisticated electronic control system. The funda- ensures that full burning is achieved.mental tasks of an engine management system are A change in timing due to engine load is alsoto manage the ignition and fuelling, as well as other required as the weaker mixture used on low loadaspects, and to refine the basic control of an engine. conditions burns at a slower rate. In this situation Many of the procedures and explanations in this further ignition advance is necessary. Greater loadchapter are generic. In other words the ignition on the engine requires a richer mixture, whichsystem explained in the next sections may be the burns more rapidly. In this case some retardationsame as the system used by a combined ignition of timing is necessary. Overall, under any condi-and fuel control system. tion of engine speed and load an ideal advance angle is required to ensure maximum pressure is achieved in the cylinder just after TDC. The ideal7.7 Ignition advance angle may also be determined by engine temperature and any risk of detonation. Spark advance is achieved in a number of ways.7.7.1 Basics The simplest of these is the mechanical systemThe purpose of the ignition system is to supply a comprising a centrifugal advance mechanism andspark inside the cylinder, near the end of the com- a vacuum (load sensitive) control unit. Manifoldpression stroke, to ignite the compressed charge of depression is almost inversely proportional to theair fuel vapour. For a spark to jump across an air engine load. I prefer to consider manifold pressure,gap of 0.6 mm under normal atmospheric condi- albeit less than atmospheric pressure; the absolutetions (1 bar) a voltage of 2 to 3 kV is required. manifold pressure (MAP) is proportional to engineFor a spark to jump across a similar gap in an load. Digital ignition systems may adjust the tim-engine cylinder having a compression ratio of 8:1 ing in relation to the temperature as well as speed
  • 125. Engine systems 109and load. The values of all ignition timing func-tions are combined either mechanically or electron-ically in order to determine the ideal ignition point. The energy storage takes place in the ignitioncoil. The energy is stored in the form of a magneticfield. To ensure that the coil is charged before theignition point a dwell period is required. Ignitiontiming is at the end of the dwell period.7.7.3 Electronic ignitionElectronic ignition is now fitted to all spark ignitionvehicles. This is because the conventional mech- Figure 7.10 Electronic ignition systemanical system has some major disadvantages. In order for a constant energy electronic igni-● Mechanical problems with the contact break- tion system to operate the dwell must increase ers not least of which is the limited lifetime. with engine speed. This will only be of benefit,● Current flow in the primary circuit is limited to however, if the ignition coil can be charged up to about 4 A or damage will occur to the contacts – its full capacity, in a very short time (the time avail- or at least the lifetime will be seriously reduced. able for maximum dwell at the highest expected● Legislation requires stringent emission limits engine speed). To this end constant energy coils are which means the ignition timing must stay in very low resistance and low inductance. Typical tune for a long period of time. resistance values are less than 1 ⍀ (often 0.5 ⍀).● Weaker mixtures require more energy from Constant energy means that, within limits, the the spark to ensure successful ignition, even at energy available to the spark plug remains constant very high engine speed. under all operating conditions. These problems can be overcome by using a Due to the high energy nature of constantpower transistor to carry out the switching func- energy ignition coils, the coil cannot be allowedtion and a pulse generator to provide the timing to remain switched on for more than a certainsignal. Very early forms of electronic ignition time. This is not a problem when the engine isused the existing contact breakers as the signal running, as the variable dwell or current limitingprovider. This was a step in the right direction circuit prevents the coil from overheating. Somebut did not overcome all the mechanical limita- form of protection must be provided, however,tions such as contact bounce and timing slip. All for when the ignition is switched on but the enginesystems nowadays are constant energy ensuring is not running. This is known as stationary enginehigh performance ignition even at high engine primary current cut off.speed. Figure 7.10 shows the circuit of a standardelectronic ignition system. The term ‘dwell’ when applied to ignition is a 7.7.4 Hall effect distributormeasure of the time during which the ignition coil The Hall effect distributor has become very popu-is charging, in other words when primary current lar with many manufacturers. Figure 7.11 showsis flowing. The dwell in conventional systems was a typical example. As the central shaft of thesimply the time during which the contact breakers distributor rotates, the chopper plate attachedwere closed. This is now often expressed as a per- under the rotor arm alternately covers and un-centage of one charge-discharge cycle. Constant covers the Hall chip. The number of vanes corres-dwell electronic ignition systems have now been ponds with the number of cylinders. In constantreplaced almost without exception by constant dwell systems the dwell is determined by theenergy systems discussed in the next section. width of the vanes. The vanes cause the Hall chip Whilst this was a very good system in its time, to be alternately in and out of a magnetic field.constant dwell still meant that at very high engine The result of this is that the device will producespeeds, the time available to charge the coil could almost a square wave output, which can then eas-only produce a lower power spark. Note that as ily be used to switch further electronic circuits.engine speed increases dwell angle or dwell per- The three terminals on the distributor arecentage remains the same but the actual time is marked ‘ϩ 0 Ϫ’; the terminals ϩ and Ϫ are for areduced. voltage supply and terminal ‘0’ is the output
  • 126. 110 Advanced automotive fault diagnosisFigure 7.11 Ignition system with Hall generatorsignal. Typically the output from a Hall effectsensor will switch between 0 V and about 8 V.The supply voltage is taken from the ignitionECU and on some systems is stabilised at about10 V to prevent changes to the output of the sen-sor when the engine is being cranked. Hall effect distributors are very common due tothe accurate signal produced and long-term reli-ability. They are suitable for use on both constantdwell and constant energy systems. Operation of aHall effect pulse generator can easily be tested witha DC voltmeter or a logic probe. Note that testsmust not be carried out using an ohmmeter as thevoltage from the meter can damage the Hall chip.7.7.5 Inductive distributorMany forms of inductive type distributors existand all are based around a coil of wire and a per-manent magnet. The example distributor shown in Figure 7.12 Inductive distributor (early type)Figure 7.12 has the coil of wire wound on the pickup and as the reluctor rotates the magnetic flux construction of the amplifier module. This tech-varies due to the peaks on the reluctor. The num- nique, when combined with dwell angle control, isber of peaks or teeth on the reluctor corresponds to known as closed loop control as the actual value ofthe number of engine cylinders. The gap between the primary current is fed back to the control stages.the reluctor and pick up can be important and A very low resistance, high power precisionmanufacturers have recommended settings. resistor is used in this circuit. The resistor is con- nected in series with the power transistor and the7.7.6 Current limiting and ignition coil. A voltage sensing circuit connected across this resistor will be activated at a pre-setclosed loop dwell voltage (which is proportional to the current), andPrimary current limiting ensures that no damage causes the output stage to hold the current at acan be caused to the system by excessive primary constant value. Figure 7.13 shows a block dia-current, but also forms a part of a constant energy gram of a closed loop dwell control system.system. The primary current is allowed to build Stationary current cut off is for when the ignitionup to its pre-set maximum as soon as possible is on but the engine not running. This is achieved inand is then held at this value. The value of this many cases by a simple timer circuit, which will cutcurrent is calculated and then pre-set during the output stage after about one second.
  • 127. Engine systems 111 Battery Ignition coil Closed Stationary Pulse Pulse loop dwell engine primary Driven Output generator shaping control cutoff stage stage Current Current limiting sensingFigure 7.13 Closed loop dwell control system7.7.7 Programmed ignition timing and dwell outputs, certain input informa- tion is required.Programmed ignition is the term used by some The crankshaft sensor consists of a permanentmanufacturers; others call it electronic spark magnet, a winding and a soft iron core. It isadvance (ESA). Constant energy electronic igni- mounted in proximity to a reluctor disc. The disction was a major step forwards and is still used has 34 teeth spaced at 10° intervals around toon countless applications. However, its limita- periphery. It has two teeth missing 180° apart, attions lay in still having to rely upon mechanical a known position BTDC. Many manufacturerscomponents for speed and load advance charac- use this technique with minor differences. As ateristics. In many cases these did not match ideally tooth from the reluctor disc passes the core of thethe requirements of the engine. sensor the reluctance of the magnetic circuit is Programmed ignition systems have a major changed. This induces a voltage in the winding,difference compared to earlier systems in that the frequency of the waveform being proportionalthey operate digitally. Information about the oper- to the engine speed. The missing tooth causes aating requirements of a particular engine is pro- ‘missed’ output wave and hence engine positiongrammed in to memory inside the ECU. The data can be determined.for storage in ROM is obtained from rigorous Engine load is proportional to manifold pres-testing on an engine dynamometer and further sure in that high load conditions produce highdevelopment work in the vehicle under various pressure and lower load conditions, such as cruise,operating conditions. Programmed ignition has produce lower pressure. Load sensors are there-several advantages. fore pressure transducers. They are either mounted● The ignition timing can be accurately matched in the ECU or as a separate unit and are con- to the individual application under a range of nected to the inlet manifold with a pipe. The pipe operating conditions. often incorporates a restriction to damp out fluc-● Other control input can be utilised such tuations and a vapour trap to prevent petrol fumes as coolant temperature and ambient air reaching the sensor. temperature. Coolant temperature measurement is carried● Starting is improved, fuel consumption is out by a simple thermistor. In many cases the reduced as are emissions and idle control is same sensor is used for the operation of the tem- better. perature gauge and to provide information to the● Other inputs can be taken into account such as fuel control system. A separate memory map is engine knock. used to correct the basic timing settings. Timing● The number of wearing components in the may be retarded when the engine is cold to assist ignition system is considerably reduced. in more rapid warm up. Combustion knock can cause serious damage toProgrammed ignition or ESA can be a separate an engine if sustained for long periods. This knocksystem or included as part of the fuel control sys- or detonation is caused by over advanced ignitiontem. In order for the ECU to calculate suitable timing. At variance with this is that an engine in
  • 128. 112 Advanced automotive fault diagnosisgeneral will run at its most efficient when the tim- longer dwell and a higher voltage a slightlying is advanced as far as possible. To achieve this shorter dwell. A Windows® shareware programthe data stored in the basic timing map will be as that simulates the ignition system (as well as manyclose to the knock limit of the engine as possible. other systems) is available for download fromThe knock sensor provides a margin for error. The my web site.sensor itself is an accelerometer often of the piezo- The output of a system such as this programmedelectric type. It is fitted in the engine block between ignition is very simple. The output stage, in com-cylinders two and three on in-line four cylinder mon with most electronic ignition, consists of aengines. Vee engine’s require two sensors, one on heavy-duty transistor which forms part of, or iseach side. The ECU responds to signals from the driven by, a Darlington pair. This is simply toknock sensor in the engine’s knock window for allow the high ignition primary current to be con-each cylinder; this is often just a few degrees each trolled. The switch off point of the coil will con-side of TDC. This prevents clatter from the valve trol ignition timing and the switch on point willmechanism being interpreted as knock. The signal control the dwell period.from the sensor is also filtered in the ECU to The high tension distribution is similar to aremove unwanted noise. If detonation is detected more conventional system. The rotor arm, how-the ignition timing is retarded on the fourth ignition ever, is mounted on the end of the camshaft withpulse after detection (four cylinder engine), in steps the distributor cap positioned over the top. Figureuntil knock is no longer detected. The steps vary 7.15 shows a programmed ignition system.between manufacturers but about 2° is typical. Thetiming is then advanced slowly in steps of say 1°over a number of engine revolutions, until the 7.7.8 Distributorless ignitionadvance required by memory is restored. This fine Distributorless ignition has all the features of pro-control allows the engine to be run very close to the grammed ignition systems but, by using a specialknock limit without risk of engine damage. type of ignition coil, outputs to the spark plugs Correction to dwell settings is required if the without the need for an HT distributor. The systembattery voltage falls, as a lower voltage supply to is generally only used on four cylinder engines asthe coil will require a slightly larger dwell figure. the control system becomes too complex forThis information is often stored in the form of a higher numbers. The basic principle is that ofdwell correction map. the ‘lost spark’. The distribution of the spark is As the sophistication of systems has increased achieved by using double ended coils, which arethe information held in the memory chips of the fired alternately by the ECU. The timing is deter-ECU has also increased. The earlier versions of mined from a crankshaft speed and position sen-programmed ignition system produced by Rover sor as well as load and other corrections. Whenachieved accuracy in ignition timing of Ϯ1.8° one of the coils is fired a spark is delivered to twowhereas a conventional distributor is Ϯ8°. The engine cylinders, either 1 and 4, or 2 and 3. Theinformation, which is derived from dynamom- spark delivered to the cylinder on the compres-eter tests as well as running tests in the vehicle, is sion stroke will ignite the mixture as normal. Thestored in ROM. The basic timing map consists of spark produced in the other cylinder will have nothe correct ignition advance for 16 engine speeds effect, as this cylinder will be just completing itsand 16 engine load conditions. exhaust stroke. A separate three-dimensional map is used Because of the low compression and thewhich has eight speed and eight temperature exhaust gases in the ‘lost spark’ cylinder the volt-sites. This is used to add corrections for engine age used for the spark to jump the gap is onlycoolant temperature to the basic timing settings. about 3 kV. This is similar to the more conven-This improves driveability and can be used to tional rotor arm to cap voltage. The spark pro-decrease the warm-up time of the engine. The duced in the compression cylinder is therefore notdata is also subjected to an additional load cor- affected.rection below 70°C. Figure 7.14 shows a flow An interesting point here is that the spark onchart representing the logical selection of the one of the cylinders will jump from the earthoptimum ignition setting. Note that the ECU will electrode to the spark plug centre. Many yearsalso make corrections to the dwell angle, both as ago this would not have been acceptable as thea function of engine speed to provide constant spark quality when jumping this way would notenergy output and due to changes in battery volt- have been as good as when it jumps from theage. A lower battery voltage will require a slightly centre electrode. However, the energy available
  • 129. Engine systems 113 Figure 7.14 Ignition calculation flow diagramFigure 7.15 Programmed ignition system component layout
  • 130. 114 Advanced automotive fault diagnosisfrom modern constant energy systems will pro-duce a spark of suitable quality in either direction. The direct ignition system (DIS) consists ofthree main components, the electronic module,a crankshaft position sensor and the DIS coil. Inmany systems a MAP sensor is integrated in themodule. The module functions in much the sameway as has been described for the electronic sparkadvance system. The crankshaft position sensor is similar inoperation to the one described in the previoussection. It is again a reluctance sensor and ispositioned against the front of the flywheel or Figure 7.16 DIS coilagainst a reluctor wheel just behind the frontcrankshaft pulley. The tooth pattern consists of35 teeth. These are spaced at 10° intervals with agap where the 36th tooth would be. The missingtooth is positioned at 90° BTDC for numbers 1and 4 cylinders. This reference position is placeda fixed number of degrees before TDC, in orderto allow the timing or ignition point to be calcu-lated as a fixed angle after the reference mark. The low tension winding is supplied with bat-tery voltage to a centre terminal. The appropriatehalf of the winding is then switched to earth inthe module. The high tension windings are sep-arate and are specific to cylinders 1 and 4, or 2and 3. Figure 7.16 shows a typical DIS coil for asix cylinder engine.7.7.9 Direct ignitionDirect ignition is in a way the follow on from dis-tributorless ignition. This system utilises an induc-tive coil for each cylinder. These coils are mounteddirectly on the spark plugs. Figure 7.17 shows across section of the direct ignition coil. The use of Figure 7.17 Direct ignition systeman individual coil for each plug ensures that the risetime for the low inductance primary winding isvery fast. This ensures that a very high voltage, this on some systems is a camshaft sensor to pro-high energy spark is produced. This voltage, which vide information as to which cylinder is on thecan be in excess of 400 kV, provides efficient initi- compression stroke. A system which does notation of the combustion process under cold starting require a sensor to determine which cylinder isconditions and with weak mixtures. Some direct on compression (engine position is known from aignition systems use capacitor discharge ignition. crank sensor) determines the information by In order to switch the ignition coils igniter initially firing all of the coils. The voltage acrossunits are used. These can control up to three coils the plugs allows measurement of the current forand are simply the power stages of the control each spark and will indicate which cylinder is onunit but in a separate container. This allows less its combustion stroke. This works because a burn-interference to be caused in the main ECU due to ing mixture has a lower resistance. The cylinderheavy current switching and shorter runs of wires with the highest current at this point will be thecarrying higher currents. cylinder on the combustion stroke. Ignition timing and dwell are controlled in A further feature of some systems is the casea manner similar to the previously described pro- when the engine is cranked over for an excessivegrammed system. The one important addition to time making flooding likely. The plugs are all
  • 131. Engine systems 115fired with multisparks for a period of time afterthe ignition is left in the on position for five sec-onds. This will burn away any excess fuel. During difficult starting conditions, multispark-ing is also used by some systems during 70°of crank rotation before TDC. This assists withstarting and then once the engine is running,the timing will return to its normal calculatedposition.7.7.10 Spark plugsFigure 7.18 shows a standard spark plug. Thecentre electrode is connected to the top terminalby a stud. The electrode is constructed of a nickelbased alloy. Silver and platinum are also used forsome applications. If a copper core is used in theelectrode this improves the thermal conductionproperties. The insulating material is ceramic based andof a very high grade. The electrically conductiveglass seal between the electrode and terminalstud is also used as a resistor. This resistor hastwo functions: firstly to prevent burn off of thecentre electrode; and secondly to reduce radiointerference. In both cases the desired effect isachieved because the resistor damps the currentat the instant of ignition. Flashover or tracking down the outside of Figure 7.18 Construction of a typical spark plugthe plug insulation is prevented by ribs. Theseeffectively increase the surface distance from theterminal to the metal fixing bolt, which is of combustion temperature and not to the efficiencycourse earthed to the engine. of the cooling system. Due to the many and varied constructional The following factors determine the thermalfeatures involved in the design of an engine, the capacity of a spark plug.range of temperatures a spark plug is exposed tocan vary significantly. The operating temperature ● insulator nose lengthof the centre electrode of a spark plug is critical. ● electrode materialIf the temperature becomes too high then pre- ● thread contact lengthignition may occur as the fuel air mixture may ● projection of the electrodebecome ignited due to the incandescence of theplug electrode. On the other hand if the electrode It has been found that a longer projection oftemperature is too low then carbon and oil foul- the electrode helps to reduce fouling problemsing can occur, as deposits are not burnt off. Fouling due to low power operation, stop go driving andof the plug nose can cause shunts (a circuit in high altitude conditions. In order to use greaterparallel with the spark gap). It has been shown projection of the electrode better quality thermalthrough experimentation and experience that the conduction is required to allow suitable heat trans-ideal operating temperature of the plug electrode fer at higher power outputs. Figure 7.19 shows theis between 400 and 900°C. heat conducting paths of a spark plug together with The heat range of a spark plug then is a meas- changes in design for heat ranges. Also shown isure of its ability to transfer heat away from the the range of part numbers for NGK plugs.centre electrode. A hot running engine will require For normal applications alloys of nickel areplugs with a higher thermal loading ability than a used for the electrode material. Chromium, man-colder running engine. Note that hot and cold ganese, silicon and magnesium are examples ofrunning of an engine in this sense refers to the the alloying constituents. These alloys exhibit
  • 132. 116 Advanced automotive fault diagnosis particular application. Plug gaps in the region of 0.6 to 1.2 mm seem to be the norm at present. 7.8 Diagnostic – ignition systems 7.8.1 Testing procedure Warning Caution/Achtung/Attention – high voltages can seriously damage your health! The following procedure is generic and with a little adaptation can be applied to any ignition system. Refer to manufacturer’s recommenda-Figure 7.19 ‘Hot’ and ‘Cold’ spark plugs tions if in any doubt. Ignition systems diagnostic chartexcellent properties with respect to corrosion and Startburn off resistance. To improve on the thermal Hand and eye checks (loose wires,conductivity compound electrodes are used. This loose switches and other obvious faults) – all connections clean and tightallows a greater nose projection for the sametemperature range as discussed in the last sec-tion. A common example of this type of plug is Check battery – must be 70% chargedthe copper core spark plug. Silver electrodes are used for specialist appli- Check supply to ignitioncations as silver has very good thermal and elec- coil (within 0.5 V of battery)trical properties. Again with these plugs noselength can be increased within the same temper-ature range. Platinum tips are used for some Spark from coil via known good HT No Yesspark plug applications due to the very high burn lead (jumps about 10 mm, but do not try a greateroff resistance of this material. It is also possible If no spark or it will distance)?because of this to use much smaller diameter only jump a short If good spark then distance continue check HT system forelectrodes thus increasing mixture accessibility. with this procedure tracking and open (colour of spark circuitsPlatinum also has a catalytic effect further accel- is not relevant)erating the combustion process. Check plug condition Check continuity Spark plug electrode gaps in general have of coil windings (leads should be a maximum resistanceincreased as the power of the ignition systems driv- (primary 0.5 to 3 of about 30 k/m) ohms, secondarying the spark has increased. The simple relationship several k ohms)between plug gap and voltage required is that as Supply to pulse Check/replace plugs Supply and earth generator ifthe gap increases so must the voltage (leaving to ‘module’ (12 V appropriate (5 or minimum supply,aside engine operating conditions). Further, the earth drop 0.5 V 10 to 12 V)energy available to form a spark at a fixed engine maximum)speed is constant, which means that a larger gap Output of pulseusing higher voltage will result in a shorter dura- Replace pulse No generator (inductive about 1 V AC when cranking, Halltion spark. A smaller gap will allow a longer dura- generator type switches 0 V to 8 V Yestion spark. For cold starting an engine and for DC)?igniting weak mixtures the duration of the spark Continuity of LT wires (0 to 0.1 ohm)is critical. Likewise the plug gap must be as largeas possible to allow easy access for the mixture Replace ‘module’ butto prevent quenching of the flame. only if all tests above are satisfactory The final choice is therefore a compromise Endreached through testing and development of a
  • 133. Engine systems 1177.8.2 Ignition fault diagnosis high voltages, pressures secondary waveform and temperatures when the engine istable under load Ignition coil Stores energy in the Resistance checksSymptom Possible fault form of magnetism of the primary and and delivers it to the secondary windingsEngine rotates but Damp ignition components distributor via thedoes not start Spark plugs worn to excess HT lead Ignition system open circuit Consists of primary and Primary: 1.5 ⍀Difficult to start Spark plugs worn to excess secondary windings (ballasted) to 3 ⍀when cold High resistance in ignition circuit Secondary: 5 to 10 k⍀Engine starts but then Ignition wiring connection Ignition Provides driver control Voltage drop acrossstops immediately intermittent switch of the ignition system the contactsErratic idle Incorrect plug gaps and is usually also used to Incorrect ignition timing cause the starter to crank HT Directs the spark Visual inspectionMisfire at idle speed Ignition coil or distributor distributor from the coil to each tracking (conducting cap tracking cylinder in a pre-set lines) and Spark plugs worn to excess sequence contaminationMisfire through all Incorrect plugs or plug gaps Engine Changes the ignition Measure the timingspeeds HT leads breaking down speed timing with engine at certain speeds Timing incorrect advance speed using an ‘advance’Lack of power Ignition timing incorrect As speed increases timing light. Refer HT components tracking the timing is advanced to dataBackfires Incorrect ignition timing Engine load Changes timing Apply a known Tracking (Vacuum) depending on engine vacuum and noteRuns on when Ignition timing incorrect advance load timing changesswitched off Carbon buildup in engine Idle speed too high Anti-run on device inoperative 7.8.4 DIS diagnosticsPinking or knocking Ignition timing incorrectunder load Ignition system electronic fault The DIS system is very reliable due to the lack of Knock sensor not working any moving parts. Some problems can be experi- enced when trying to examine HT oscilloscope pat-Figure 7.20 shows a typical ignition timing light, terns due to the lack of a king lead. This can oftenessential to ensure correct settings where these be overcome with a special adapter but it is still nec-are adjustable, or to check programmed advance essary to move the sensing clip to each lead in turn.systems for correct operation. The DIS coil can be tested with an ohmmeter. The resistance of each primary winding should be 0.5 ⍀ and the secondary windings between 11 and7.8.3 Ignition components and 16 k⍀. The coil will produce in excess of 37 kV intesting an open circuit condition. The plug leads have integral retaining clips to prevent water ingressComponent Description Test method and vibration problems. The maximum resistance for the HT leads is 30 k⍀ per lead.Spark plug Seals electrodes for Compare nose No service adjustments are possible with this the spark to jump condition to a system with the exception of octane adjustment across in the cylinder. manufacturer’s chart Must withstand very Inspect ignition on some models. This involves connecting two pins together on the module for normal operation, or earthing one pin or the other to change to a dif- ferent fuel. The actual procedure must be checked with the manufacturer for each particular model. 7.8.5 Spark plug diagnostics Examination of the spark plugs is a good way of assessing engine and associated systems condition. Figure 7.21 a) shows a new plug and b) to f) showFigure 7.20 Ignition timing light various conditions with diagnostic notes added.
  • 134. 118 Advanced automotive fault diagnosis a) New spark plug Use this image to compare with used spark plugs. Not in particular, on this standard design, how the end of the nose is flat and that the earth/ground electrode is a consistent size and shape. b) Carbon fouled (standard plug) This plug has black deposits over the centre electrode and insulator in particular. It is likely that this engine was running too rich – or on an older vehicle the choke was used excessively. However, carbon fouling may also be due to: ● Poor quality spark due to ignition fault ● Incorrect plug gap ● Over retarded timing ● Loss of cylinder compression ● Prolonged low speed driving ● Incorrect (too cold) spark plug fitted. c) Deposits The deposits on this plug are most likely to be caused by oil leaking into the cylinder. Alterna- tively, poor quality fuel mixture supply or very short, cold engine operation could result in a similar condition.Figure 7.21(a,b,c)
  • 135. Engine systems 119 d) Damaged insulation A plug that is damaged in this way is because of either overheating or impact damage. Impact is most likely in this case. The damage can of course be caused as the plug is being fitted! However, in this case a possible cause would be that the reach was too long for the engine and the piston hit the earth/ground electrode, closing up the gap and breaking the insulation. e) Carbon fouled (platinum plug) The carbon build upon this plug would suggest an incorrect mixture. However, before diagnos- ing a fault based on spark plug condition, make sure the engine has been run up to temperature – ideally by a good road test. The engine from which this plug was removed is in good condi- tion – it had just been started from cold and only run for a few minutes. f) Overheating When a plug overheats the insulator tip becomes glossy and/or they are blistered or melted away. The electrodes also wear quickly. Excessive overheating can result in the electrodes melting and serious piston damage is likely to occur. Causes of overheating are: ● Over advanced ignition ● Mixture too lean ● Cooling system fault ● Incorrect plug (too hot) ● Incorrect fuel (octane low).Figure 7.21 (d,e,f) Spark plug diagnostics
  • 136. 120 Advanced automotive fault diagnosis intake manifold drawing the vapour7.9 Emissions through the charcoal canister. This must be controlled by the manage-7.9.1 Introduction ment system, however, as even a 1% concentration of fuel vapour wouldThe following table lists the four main exhaust shift the lambda value by 20%. This isemissions which are hazardous to health, together done by using a ‘purge valve’, which under some conditions is closedwith a short description of each. (full load and idle for example) and can be progressively opened underSubstance Description other conditions. The system moni- tors the effect by use of the lambdaCarbon monoxide This gas is very dangerous even in sensor signal(CO) low concentrations. It has no smell or Crankcase fumes Hydrocarbons become concentrated taste and is colourless. When inhaled (blow by) in the crankcase mostly due to it combines in the body with the red pressure blowing past the piston blood cells preventing them from rings. These gases must be conducted carrying oxygen. If absorbed by the back into the combustion process. body it can be fatal in a very short time This is usually via the air intakeNitrogen oxides Oxides of nitrogen are colourless and system. This is described as positive(NOx) odourless when they leave the engine crankcase ventilation but as soon as they reach the atmosphere and mix with more oxygen, nitrogen oxides are formed. They are 7.9.2 Exhaust gas recirculation reddish brown and have an acrid and pungent smell. These gasses damage (EGR) the body’s respiratory system when This technique is used primarily to reduce peak inhaled. When combined with water vapour nitric acid can be formed which combustion temperatures and hence the produc- is very damaging to the windpipe and tion of nitrogen oxides (NOx). EGR can be either lungs. Nitrogen oxides are also a internal due to valve overlap, or external via a sim- contributing factor to acid rain ple arrangement of pipes and a valve (Figure 7.22Hydrocarbons (HC) A number of different hydrocarbons shows an example) connecting the exhaust mani- are emitted from an engine and are fold back to the inlet manifold. A proportion of part or unburnt fuel. When they mix exhaust gas is simply returned to the inlet side of with the atmosphere they can help to form smog. It is also believed that the engine. hydrocarbons may be carcinogenic This process is controlled electronically asParticulate matter This heading in the main covers lead determined by a ROM in the ECU. This ensures(PM) and carbon. Lead was traditionally that driveability is not effected and also that the added to petrol to slow its burning rate of EGR is controlled. If the rate is too high, rate to reduce detonation. It is then the production of hydrocarbons increases. detrimental to health and is thought to cause brain damage especially in One drawback of EGR systems is that they children. Lead will eventually be can become restricted by exhaust residue over a phased out as all new engines now period of time thus changing the actual percent- run on unleaded fuel. Particles of age of recirculation. However, valves are now soot or carbon are more of a problem available that reduce this particular problem. on diesel fuelled vehicles and these now have limits set by legislationThe following table describes two further sourcesof emissions from a vehicle.Source CommentsFuel evaporation Fuel evaporation causes hydrocarbonsfrom the tank and to be produced. The effect is greatersystem as temperature increases. A charcoal canister is the preferred method for reducing this problem. The fuel tank is usually run at a pressure just under atmospheric by a connection to the Figure 7.22 EGR valve
  • 137. Engine systems 1217.9.3 Catalytic converters the delay in the catalyst reaching this temperature. This is known as catalyst light off time. VariousStringent regulations in most parts of the world methods have been used to reduce this time as sig-have made the use of a catalytic converter almost nificant emissions are produced before light offindispensable. The three-way catalyst (TWC) is occurs. Electrical heating is one solution, as is aused to great effect by most manufacturers. It is a form of burner which involves lighting fuel insidevery simple device and looks similar to a stand- the converter. Another possibility is positioningard exhaust box. Note that in order to operate the converter as part of the exhaust manifold andcorrectly, however, the engine must be run at or down pipe assembly. This greatly reduces light offvery near to stoichiometry. This is to ensure that time but gas flow problems, vibration and exces-the right ‘ingredients’ are available for the cata- sive temperature variations can be problems thatlyst to perform its function. reduce the potential life of the unit. Figure 7.23 shows some new metallic sub- Catalytic converters can be damaged in twostrates for use inside a catalytic converter. There ways. The first is by the use of leaded fuel whichare many types of hydrocarbons but the example causes lead compounds to be deposited on theillustrates the main reaction. Note that the reac- active surfaces thus reducing effective area. Thetions rely on some CO being produced by the second is engine misfire which can cause the cat-engine in order to reduce the NOx. This is one of alytic converter to overheat due to burning insidethe reasons that manufacturers have been forced the unit. BMW, for example, use a system on someto run the engine at stoichiometry. The legisla- vehicles where a sensor monitors output of thetion has tended to stifle the development of lean ignition HT system and will not allow fuel to beburn techniques. The fine details of the emission injected if the spark is not present.regulations can in fact have a very marked effect For a catalytic converter to operate at its opti-on the type of reduction techniques used. The mum conversion rate to oxidise CO and HC whilstmain reactions in the ‘cat’ are as follows: reducing NOx, a narrow band within 0.5% of● 2CO ϩ O2 → 2CO2 lambda value 1 is essential. Lambda sensors in● 2C2H6 ϩ 2CO → 4CO2 ϩ 6H2O use at present tend to operate within about 3% of● 2NO ϩ 2CO → N2 ϩ 2CO2 the lambda mean value. When a catalytic con- verter is in prime condition this is not a problemNoble metals are used for the catalysts; platinum due to storage capacity within the converter forpromotes the oxidation of HC and CO, and CO and O2. Damaged converters, however, cannotrhodium helps the reduction of NOx. The whole store sufficient quantity of these gases and hencethree-way catalytic converter only contains about become less efficient. The damage as suggestedthree to four grams of the precious metals. earlier in this section can be due to overheating The ideal operating temperature range is from or by ‘poisoning’ due to lead or even silicon. Ifabout 400 to 800°C. A serious problem to counter is the control can be kept within 0.5% of lambdaFigure 7.23 Catalytic converter metallic substrates
  • 138. 122 Advanced automotive fault diagnosisthe converter will continue to be effective even if 7.10.2 Emissions fault diagnosisdamaged to some extent. Sensors are becoming tableavailable which can work to this tolerance. Asecond sensor fitted after the converter can be Symptom Possible causeused to ensure ideal operation. EGR valve sticking Buildup of carbon Electrical fault High CO and high HC Rich mixture7.10 Diagnostics – Blocked air filter Damaged catalytic converteremissions Engine management system fault Low CO and high HC Misfire Fouled plug(s)7.10.1 Testing procedure Weak mixture Low CO and low or Exhaust leakIf the reported fault is incorrect exhaust emis- normal HC Fouled injectorsions the following procedure should be utilised. Figure 7.24 is typical of the emissions dataavailable. 7.11 Fuel injection 7.11.1 Introduction The ideal air fuel ratio is about 14.7:1. This is the Emissions systems diagnostic chart theoretical amount of air required to completely Start burn the fuel. It is given a ‘lambda (l)’ value of 1. l ϭ actual air quantity Hand and eye checks (loose wires, loose pipes, blocked ÷ theoretical air quantity filters and other obvious faults) – all connections clean and tight Air fuel ratio is altered during the following operat- ing conditions of an engine to improve its perform- ance, driveability, consumption and emissions: Run the vehicle up to temperature by road testing – note any unusual conditions ● cold starting richer mixture is needed to compensate for fuel condensation and improve Connect revcounter and driveability; connect exhaust analyser ● load or acceleration richer to improve performance; Using the throttle pedal, hold ● cruise or light loads weaker for economy; the engine speed at about 3000 rev/min for 30 seconds ● overrun very weak (if any) fuel, to improve emissions and economy. Allow the engine to idle, check The more accurately the air fuel ratio is controlled idle speed take gas readings when stable (usually after just a to cater for external conditions, then the better the few seconds) overall operation of the engine. The major advantage, therefore, of a fuel injec- tion system is accurate control of the fuel quan- No Readings compare Yes Carry out adjustments with manufacturer’s tity injected into the engine. The basic principle recommended settings? of fuel injection is that if petrol is supplied to an Remove all test equipment injector (electrically controlled valve), at a con- stant differential pressure, then the amount of Yes fuel injected will be directly proportional to the injector open time. No Readings compareCheck EGR systemand check for leaks with manufacturer’s Most systems are now electronically controlled recommended settings? even if containing some mechanical metering components. This allows the operation of the Check enginemanagement system injection system to be very closely matched to the requirements of the engine. This matching process End is carried out during development on test beds and
  • 139. Engine systems 123 Figure 7.24 Typical emissions data Pressure regulator Injector Hot wire mass air flow meter Temp. sensor Throttle position Idle speed λ-Sensor switch actuator Fuel filter Electronic Electric Figure 7.25 LH-Jetronic fuel control unit fuel pump injectiondynamometers, as well as development in the car. 7.11.2 Injection systemsThe ideal operating data for a large number of Fuel injection systems can be classified into twoengine operating conditions is stored in a ROM in main categories, single point injection and multi-the ECU. Close control of fuel quantity injected point injection. Figure 7.26 shows these tech-allows the optimum setting for mixture strength niques together with a third known as continuouswhen all operating factors are taken into account. injection (K/KE Jetronic). Depending on the Further advantages of electronic fuel injection sophistication of the system, idle speed and idlecontrol are that overrun cut off can easily be mixture adjustment can be either mechanicallyimplemented, fuel can be cut at the engines rev or electronically controlled.limit and information on fuel used can be sup- Figure 7.27 shows a block diagram of inputs andplied to a trip computer. Figure 7.25 shows a typ- outputs common to most fuel injection systems.ical fuel injection system layout for LH-Jetronic. Note that the two most important input sensors to
  • 140. 124 Advanced automotive fault diagnosis Figure 7.26 Petrol injection systems Engine speed Engine load Coolant Fuel temperature injectors Throttle Idle speed position control Exhaust gas O2 content Figure 7.28 Engine management ECU 7.11.3 Fuel injection components Battery voltage Many of the sensors and actuators associated with fuel injection are covered in Chapter 6. Figure 7.29Figure 7.27 Fuel injection system block diagram shows those associated with the LH-Jetronic injec- tion system. Starting at the top left and working clockwise the components are as follows.the system are speed and load. The basic fuellingrequirement is determined from these inputs in a Air flow metersimilar way to the determination of ignition timing. An engine’s fuelling requirements are stored as The type shown is a hot-wire meter. This allowspart of a ROM chip in the ECU. When the ECU has direct measurement of air mass as temperaturedetermined the ‘look up value’ of the fuel required compensation is built in. The air quantity helps(injector open time), corrections to this figure can to determine the fuel required.be added for battery voltage, temperature, throttlechange or position and fuel cut off. Figure 7.28 Electronic control unit (ECU)shows an injection system ECU. This is also referred to as the electronic control Idle speed and fast idle are also generally con- module (ECM). The circuitry to react to the sen-trolled by the ECU and a suitable actuator. It is sor signals by controlling the actuators is in thealso possible to have a form of closed loop control ECU. The data is stored in ROM.with electronic fuel injection. This involves alambda sensor to monitor exhaust gas oxygen con- Fuel pumptent. This allows very accurate control of the mix- Pressurised fuel is supplied to the injectors. Mostture strength, as the oxygen content of the exhaust pumps work on the centrifugal roller principle.is proportional to the air fuel ratio. The signal The pump ensures a constant supply of fuel tofrom the lambda sensor is used to adjust the injec- the fuel rail. The volume in the rail acts as a swamptor open time. to prevent pressure fluctuations as the injectors
  • 141. Engine systems 125Figure 7.29 Injection components in positionoperate. The pump must be able to maintain a Fuel pressure regulatorpressure of about 3 bar. This device is to ensure a constant differential pressure across the injectors. It is a mechanicalFuel filter device and has a connection to the inlet manifold.The fuel supplied to the injectors must be freefrom any contamination or else the injector noz- Throttle position switchzle will be damaged or blocked. This is used to supply information as to whether the throttle is at idle, full load or somewhere inLambda sensor between.The quantity of oxygen in the exhaust, whenaccurately measured, ensures that the fuel air mix-ture is kept within the lambda window (0.97 to 7.11.4 Fuel mixture calculation1.03). The quantity of fuel to be injected is determined primarily by the quantity of air drawn into theTemperature sensor engine. This is dependent on two factors:A simple thermistor is used to determine the ● engine speed (rev/min);engine coolant temperature. ● engine load (inlet manifold pressure).Fuel injectors This speed load characteristic is held in the ECU memory in ROM lookup tables.These are simple solenoid operated valves A sensor connected to the manifold by a pipedesigned to operate very quickly and produce a senses manifold absolute pressure. The sensorfinely atomised spray pattern. is fed with a stabilised 5 V supply and transmits an output voltage according to the pressure. TheIdle or fast idle control actuator sensor is fitted away from the manifold and henceThe rotary actuator is shown here. It is used to a pipe is required to connect it. The output signalprovide extra air for cold fast idle conditions as varies between about 0.25 V at 0.17 bar to aboutwell as controlling idle speed. It is supplied with 4.75 V at 1.05 bar. The density of air varies witha variable duty cycle square wave. temperature such that the information from the
  • 142. 126 Advanced automotive fault diagnosisMAP sensor on air quantity will be incorrect over 7.12 Diagnostics – fuelwide temperature variations. An air temperaturesensor is used to inform the ECU of the inlet air injection systemstemperature such that the quantity of fuel injectedmay be corrected. As the temperature of air 7.12.1 Testing proceduredecreases its density increases and hence the Warningquantity of fuel injected must also be increased. Caution/Achtung/Attention – burning fuel canThe other method of sensing engine load is direct seriously damage your health!measurement of air intake quantity using a hot-wire meter or a flap type air flow meter. The following procedure is generic and with a In order to operate the injectors the ECU needs little adaptation can be applied to any fuel injec-to know, in addition to air pressure, the engine tion system. Refer to manufacturer’s recommen-speed to determine the injection quantity. The dations if in any doubt. It is assumed that thesame flywheel sensor used by the ignition system ignition system is operating correctly. Most testsprovides this information. All four injectors are carried out while cranking the engine.operate simultaneously once per engine revolution,injecting half of the required fuel. This helps toensure balanced combustion. The start of injec- 7.12.2 Fuel injection faulttion varies according to ignition timing. diagnosis table A basic open period for the injectors is deter-mined by using the ROM information relating to Symptom Possible faultmanifold pressure and engine speed. Two correc- Engine rotates but No fuel in the tank!tions are then made, one relative to air tempera- does not start Air filter dirty or blockedture and another depending on whether the engine Fuel pump not runningis idling, at full or partial load. No fuel being injected The ECU then carries out another group of Difficult to start Air filter dirty or blockedcorrections, if applicable: when cold Fuel system wiring fault Enrichment device not working● after start enrichment; Coolant temperature sensor● operational enrichment; short circuit● acceleration enrichment; Difficult to start Air filter dirty or blocked● weakening on deceleration; when hot Fuel system wiring fault Coolant temperature sensor open● cut off on overrun; circuit● reinstatement of injection after cut off; Engine starts but then Fuel system contamination● correction for battery voltage variation. stops immediately Fuel pump or circuit fault (relay)Under starting conditions the injection period is cal- Intake system air leakculated differently. This is determined mostly from Erratic idle Air filter blocked Inlet system air leaka set figure varied as a function of temperature. Incorrect CO setting The coolant temperature sensor is a thermistor Idle air control valve not operatingand is used to provide a signal to the ECU relat- Fuel injectors not spraying correctlying to engine coolant temperature. The ECU can Misfire through all Fuel filter blockedthen calculate any corrections to fuel injection speeds Fuel pump delivery lowand ignition timing. The operation of this sensor Fuel tank ventilation system blockedis the same as the air temperature sensor. Engine stalls Idle speed incorrect The throttle potentiometer is fixed on the CO setting incorrect Fuel filter blockedthrottle butterfly spindle and informs the ECU of Air filter blockedthrottle position and rate of change of throttle Intake air leakposition. The sensor provides information on accel- Idle control system not workingeration, deceleration and whether the throttle is Lack of power Fuel filter blockedin the full load or idle position. It comprises a Air filter blockedvariable resistance and a fixed resistance. As is Low fuel pump deliverycommon with many sensors a fixed supply of 5 V Fuel injectors blockedis provided and the return signal will vary Backfires Fuel system fault (air flow sensor on some cars)approximately between 0 and 5 V. The voltage Ignition timingincreases as the throttle is opened.
  • 143. Engine systems 127 Fuel injection system diagnostic chart Start Hand and eye checks (loose wires, loose switches and other faults No MIL off and such as filters) – all system ok? No Yes connections clean and tight. Check battery – must be 70% charged Follow route identified by Yes the DTC – check sensor, DTC available? actuator or wiring as appropriate No Check fuel pressure at rail (multipoint systems it will be about 2.5 Yes No bar but check)? Is injector operation ok – (suitable Supply voltage to pump (within spray pattern or dwell reading across 0.5 V battery – pump or regulator fault injector supply) if supply is ok) Check supply circuits from main Check pump relay and circuit relay (battery volts minimum) (note in mostcases the ECU closes the relay but this may be by passed on cranking) Continuity of injector wiring (0 to 0.2) Check continuity of windings – (note that many injectors are connected in parallel) Ensure all connections (electrical and fuel are remade correctly) – return to earlier stage if necessary Sensor readings and continuity of wiring (0 ohms for the wiring sensors will vary with type) If no fuel is being injected and all tests so far are ok then suspect ECU End7.13 Diesel injection The timing of a diesel fuel injection pump to an engine is usually done using start of delivery as the reference mark. The actual start of injec-7.13.1 Introduction tion, in other words when fuel starts to leave theThe basic principle of the four stroke diesel injector, is slightly later than start of delivery, asengine is very similar to the petrol system. The this is influenced by the compression ratio of themain difference is that the mixture formation engine, the compressibility of the fuel and thetakes place in the cylinder combustion chamber length of the delivery pipes. This timing has aas the fuel is injected under very high pressure. great effect on the production of carbon particlesThe timing and quantity of the fuel injected is (soot), if too early, and increases the hydrocar-important from the usual issues of performance, bon emissions, if too late.economy and emissions. The duration of the injection is expressed in Fuel is metered into the combustion chamber degrees of crankshaft rotation in milliseconds.by way of a high pressure pump connected to This clearly influences fuel quantity but the rateinjectors via heavy duty pipes. When the fuel is of discharge is also important. This rate is notinjected it mixes with the air in the cylinder and constant due to the mechanical characteristics ofwill self ignite at about 800°C. The mixture for- the injection pump.mation in the cylinder is influenced by the fol- Pressure of injection will affect the quantity oflowing factors. fuel but the most important issue here is the effect
  • 144. 128 Advanced automotive fault diagnosisFigure 7.30 Bosch VR Pump (Source: Bosch Press)on atomisation. At higher pressures the fuel will mechanical with all current systems. The followingatomise into smaller droplets with a correspon- advantages are apparent over the non-electronicding improvement in the burn quality. Indirect control system:injection systems use pressures up to about 350 ● more precise control of fuel quantity injected;bar and direct injection systems can be up to about ● better control of start of injection;1000 bar. Emissions of soot are greatly reduced by ● idle speed control;higher pressure injection. ● control of exhaust gas recirculation; The direction of injection must match very ● drive by wire system (potentiometer on throt-closely the swirl and combustion chamber design. tle pedal);Deviations of only 2° from the ideal can greatly ● an anti-surge function;increase particulate emissions. ● output to data acquisition systems, etc.; Diesel engines do not in general use a throttle ● temperature compensation;butterfly as the throttle acts directly on the injec- ● cruise control.tion pump to control fuel quantity. At low speedsin particular the very high excess air factor ensures Because fuel must be injected at high pressurecomplete burning and very low emissions. Diesel the hydraulic head, pressure pump and drive elem-engines operate where possible with an excess air ents are still used. An electromagnetic movingfactor even at high speeds. iron actuator adjusts the position of the control Figure 7.30 shows a typical diesel fuel injec- collar, which in turn controls the delivery stroketion pump. Detailed operation of the components and therefore the injected quantity of fuel. Fuelis beyond the scope of this book. The principles pressure is applied to a roller ring and this con-and problems are the issues under consideration, trols the start of injection. A solenoid operatedin particular the way electronics can be employed valve controls the supply to the roller ring. Theseto solve some of the problems. actuators together allow control of start of injec- tion and injection quantity. Ideal values for fuel quantity and timing are7.13.2 Electronic control of stored in memory maps in the ECU. The injecteddiesel injection fuel quantity is calculated from the accelerator position and the engine speed. Start of injectionThe advent of electronic control over the diesel is determined from the following:injection pump has allowed many advances overthe purely mechanical system. The production ● fuel quantity;of high pressure and injection is, however, still ● engine speed;
  • 145. Engine systems 1291 Air mass meter 12 Engine ECU 23 High pressure pump H SC O B4 Common rail5 Injectors 36 Engine speed 5 sensor BOSC H7 Coolant temp. 4 9 sensor 78 Filter 89 Accelerator pedal sensor 6 Figure 7.31 Common rail diesel system components (Source: Bosch Press)● engine temperature; combustion phase during the main injection● air pressure. period, is softer and more efficient. Fuel injection pressures are varied – through-The ECU is able to compare start of injection out the engine speed and load range – to suit thewith actual delivery from a signal produced by instantaneous conditions of driver demand andthe needle motion sensor in the injector. engine speed and load conditions. Data input, from Control of exhaust gas recirculation is a sim- other vehicle system ECUs, is used to further adaptple solenoid valve. This is controlled as a func- the engine output, to suit changing conditions else-tion of engine speed, temperature and injected where on the vehicle. Examples are traction con-quantity. The ECU is also in control of the stop trol, cruise control and automatic transmissionsolenoid and glow plugs via a suitable relay. gearshifts. The electronic diesel control (EDC) module7.13.3 Common rail (CR) diesel carries out calculations to determine the quantitysystems of fuel delivered. It also determines the injection timing based on engine speed and load conditions.The development of diesel fuel systems is con- The actuation of the injectors, at a specifictinuing, with many new electronic changes to the crankshaft angle, and for a specific duration iscontrol and injection processes. One of the latest made by signal currents from the EDC module.developments is the ‘common rail’ system, oper- A further function of the EDC module is to con-ating at very high injection pressures. It also has trol the accumulator (rail) pressure.piloted and phased injection to reduce noise and In summary, common rail diesel fuel injectionvibration. systems consist of four main component areas. The common rail system (Figure 7.31) hasmade it possible, on small high speed diesel 1. Low pressure delivery.engines, to have direct injection when previously 2. High pressure delivery with a high pressurethey would have been of indirect injection design. pump and accumulator (the rail).These developments are showing improvements 3. Electronically controlled injectors (Figure 7.32).in fuel consumption and performance of up to 4. Electronic control unit and associated sensors20% over the earlier indirect injection engines and switches.of a similar capacity. The common rail injection The main sensors for calculation of the fuel quan-system can be used on the full range of diesel tity and injection advance requirements are theengine capacities. accelerator pedal sensor, crankshaft speed and The combustion process, with common rail position sensor, air-mass meter and the engineinjection, is improved by a pilot injection of a coolant temperature sensor.very small quantity of fuel, at between 40° and90° btdc. This pilot fuel ignites in the compress-ing air charge so that the cylinder temperatureand pressure are higher than in a conventional 7.13.4 Diesel exhaust emissionsdiesel injection engine at the start of injection. Exhaust emissions from diesel engines have beenThe higher temperature and pressure reduces reduced considerably by changes in the design ofignition lag to a minimum, so that the controlled combustion chambers and injection techniques.
  • 146. 130 Advanced automotive fault diagnosisFigure 7.32 Sectioned details of the CR injector (Source: Bosch Press)More accurate control of start of injection and are always run with excess air to ensure betterspill timing has allowed further improvements and more efficient burning of the fuel. A normalto be made. Electronic control has also made a catalyst therefore will not strip the oxygen off thesignificant contribution. A number of further tech- NOx to oxidise the hydrocarbons because theniques can be employed to control emissions. excess oxygen will be used. Special NOx convert- Overall the emissions from diesel combustion ers are becoming available.are far lower than emission from petrol combus-tion. The CO, HC and NOx emissions are lower 7.13.6 Filtersmainly due to the higher compression ratio andexcess air factor. The higher compression ratio To reduce the emission of particulate matter (soot),improves the thermal efficiency and thus lowers filters can be used. These can vary from a finethe fuel consumption. The excess air factor ensures grid design made from a ceramic material to cen-more complete burning of the fuel. trifugal filters and water trap techniques. The prob- The main problem area is that of particulate lem to overcome is that the filters can get blocked,emissions. These particle chains of carbon mol- which adversely affects the overall performance.ecules can also contain hydrocarbons, aldehydes Several techniques are employed including cen-mostly. The dirt effect of this emission is a pollu- trifugal filters.tion problem but the possible carcinogenic effectof this soot gives cause for concern. The diameterof these particles is only a few ten thousandths of 7.14 Diagnostics – diesela millimetre. This means they float in the air and injection systemscan be inhaled. In much the same way as with petrol enginesEGR is employed primarily to reduce NOx emis- 7.14.1 Test equipmentsions by reducing the reaction temperature in the Note: You should always refer to the manufac-combustion chamber. However if the percentage of turer’s instructions appropriate to the equipmentEGR is too high, increased hydrocarbons and soot you are using.are produced. This is appropriate to turbochargedengines such that if the air is passed through an Smoke meter (Figure 7.33)intercooler, as well as improvements in volumetricefficiency, lower temperature will again reduce the This is an essential device in the UK and otherproduction of NOx. The intercooler is fitted in the countries where the level of smoke in the exhaustsame way as the cooling system radiator. forms part of the annual test. Most devices use infrared light to ‘count’ the number of soot parti- cles in the exhaust sample. This particulate matter7.13.5 Catalytic converter – (PM) is highly suspected of being carcinogenic.dieselOn a diesel engine a catalyst can be used to reduce Injector tester (Figure 7.34)the emission of hydrocarbons but will have less The pressure required to ‘crack’ (lift the nozzle)effect on nitrogen oxides. This is because diesels on an injector can be tested.
  • 147. Engine systems 131 7.14.3 Diesel engine smoke Diesel fuel is a hydrocarbon fuel. When it is burned in the cylinder it will produce carbon dioxide and water. There are, however, many cir- cumstances under which the fuel may not be com- pletely burned and one of the results is smoke. Despite the fact that diesel engines are designed to run under all conditions with an excess of air, problems still occur. Very often these smoke prob- lems are easily avoided by proper maintenance and servicing of the engine and its fuel system.Figure 7.33 Smoke meter The emission of smoke is usually due to a short- age of air (oxygen). If insufficient air is available for complete combustion then unburnt fuel will be exhausted as tiny particles of fuel (smoke). The identification of the colour of diesel smoke and under what conditions it occurs can be help- ful in diagnosing what caused it in the first place. Poor quality fuel reduces engine performance, increases smoke and reduces engine life. There are three colours of smoke; white, blue and black. All smoke diagnosis tests must be carried out with the engine at normal operating temperature. White or grey smokeFigure 7.34 Diesel injector tester White smoke is vaporised unburnt fuel and is caused by there being sufficient heat in the cylin- der to vaporise it but not enough remaining heat to burn it. All diesel engines generate white smoke7.14.2 Diesel injection fault when starting from cold and it is not detrimental todiagnosis table the engine in any way – it is a diesel characteristic. Possible causes of white smoke are listed below.Symptom Possible fault ● Faulty cold starting equipment cold enginesEngine rotates but No fuel in the tank! suffer from a delay in the combustion process.does not start Cam belt broken A cold start unit is fitted to advance the injec- Fuel pump drive broken tion timing to counteract this delay. This means Open circuit supply to stop solenoid that white smoke could be a cold start unit Fuel filter blocked problem.Excessive smoke Refer to the next section ● Restrictions in the air supply a partiallyLack of power Timing incorrect blocked air cleaner will restrict the air supply; Governor set too low an easy cause to rectify but often overlooked. Injector nozzles worn Injector operating pressure incorrect Incidentally, a blocked air cleaner element atDifficult to start Timing incorrect light load in the workshop becomes a black Glow plugs not working smoke problem when the engine is underFuel smell in the car Fuel lines leaking load. In both cases there will not be sufficient Leak off pipes broken air entering the cylinder for the piston to com-Diesel knock Timing incorrect press and generate full heat for combustion.(particularly when cold) Glow plug hold on for idle circuit ● Cold running check the cooling system not working thermostat to see if the correct rated thermo-Engine oil contaminated Piston broke (like me after a good stat is fitted.with fuel holiday!) ● Incorrect fuel injection pump timing if Worn piston rings fuel is injected late (retarded timing) it may be Excessive fuel injected vaporised but not burned.
  • 148. 132 Advanced automotive fault diagnosis● Poor compressions poor compressions may Ignition switch lead to leakage during the compression stroke Coolant temperature sensor ECU and inevitably less heat would be generated.● Leaking cylinder head gasket if coolant were leaking into the combustion area, the 12 V result would be less temperature in the cylinder WL glow causing white smoke. Steam may also be gen- plugs erated if the leak is sufficient. All internal com- Low valve bustion engines have water as a by-product Sensing resistor from burning fuel – you will have noticed your Figure 7.35 Glow plug circuit own car exhaust, especially on a cold morning. of glow plugs used; most are 12 V and connectedBlue smoke in parallel but some are connected in series (4 ϫBlue smoke is almost certainly a lubricating oil 3 V plugs). To check the operation of most 12 Vburning problem. Possible causes of blue smoke glow plug circuits, use the following steps.are listed: 1. Hand and eye checks.● incorrect grade of lubricating oil; 2. Battery condition – at least 70%.● worn or damaged valve stem oil seals, valve 3. Engine must be cold – it may be possible to guides or stems where lubricating oil is get- simulate this by disconnecting the tempera- ting into the combustion chamber; ture sensor.● worn or sticking piston rings; 4. Voltage supplied to plugs when ignition is● worn cylinder bores. switched on (spring loaded position in some cases) – 10 to 12 V.Black smoke 5. Warning light operation – should go out afterBlack smoke is partly burned fuel. Possible causes a few seconds.are listed below. 6. Voltage supplied to plugs while cranking – 9 to 11 V.● Restriction in air intake system a blocked 7. Voltage supplied to plugs after engine has air cleaner element will not let enough air in started – 0 V or if silent idle system is used 5 to burn all the fuel. to 6 V for several minutes.● Incorrect valve clearances excessive valve 8. Same tests with engine at running temperature – clearances will cause the valves not to fully glow plugs may not be energised or only for open and to close sooner. This is another form the starting phase. of insufficient air supply.● Poor compressions air required for com- bustion may leak from the cylinder. 7.14.5 Diesel systems● Defective or incorrect injectors check the It is recommended that when the injection pump injector to see if the spray is fully atomised or the injectors are diagnosed as being at fault, and solid fuel is not being injected. reconditioned units should be fitted. Other than● Incorrect fuel injection pump timing this basic settings of timing, idle speed and governor is less likely because the timing would need to speed, major overhaul is often required. Figure be advanced to the point where additional 7.36 shows a general diagnosis pattern for diesel engine noise would be evident. systems produced by ‘Autologic’.● Low boost pressure if a turbocharger is fit- ted and is not supplying enough air for the fuel injected this is another form of air starvation. 7.15 Engine management7.14.4 Glow plug circuit 7.15.1 IntroductionFigure 7.35 shows a typical glow plug circuit con- As the requirement for lower and lower emis-trolled by an ECU. Most timer circuits put the sions continues together with the need for betterglow plugs on for a few seconds prior to cranking. performance, other areas of engine control areA warning light may be used to indicate the ‘ready’ constantly being investigated. This is becomingcondition to the driver. Take care to note the type even more important as the possibility of carbon
  • 149. Engine systems 133 Engine does not start Check battery voltage Check for fuel supply Check vehicle security Check glow plug system is disarmed operation Check lift pump operation Check condition of air filter Check fuel filter is Check glow plug clean and for fuel at resistance Check valve clearances injection pump Check compression Check injectors for Check engine stop pressures spray pattern andsolenoid is not activated buildup of deposits Check valve timing is correct Check for air in Check starter turns fuel system above 150 rev/min Check injection pump timing Figure 7.36 General diagnosis patterndioxide emissions being included in the regula- valves. The length of the inlet tract has an effecttions increases. Some of the current and potential on the frequency of these waves.areas for further control of engine operation are With the widespread use of twin cam engines,included in this section. Most of the common one cam for the inlet valves and one for the exhaustareas of ‘control’ have been covered under either valves, it is possible to vary the valve overlap whileIgnition (Section 7.7) or Fuel injection (Section the engine is running. Honda has a system that7.11). The main areas of control are as follows: improves the power and torque range by opening both of the inlet valves only at higher speed.● ignition timing; A BMW system uses oil pressure controlled● dwell angle; by valves to turn the cam with respect to its drive● fuel quantity; gear. This alters the cam phasing or relative pos-● idle speed. ition. The position of the cams is determined fromFurther areas of engine control may include: a suitable map held in ROM in the control unit.● EGR;● canister purge; 7.15.2 Closed loop lambda● valve timing; control● inlet manifold length; Current regulations have almost made closed● closed loop lambda control. loop control of air fuel mixture in conjunctionIt is not possible for an engine to operate at its with a three way catalytic converter mandatory.best volumetric efficiency with fixed manifolds. It is under discussion that a lambda value of oneThis is because the length of the inlet tract deter- may become compulsory for all operating condi-mines the velocity of the intake air and in particu- tions, but this is yet to be agreed.lar the propagation of the pressure waves set up Lambda control is a closed loop feedback sys-by the pumping action of the cylinders. These tem in that the signal from a lambda sensor instanding waves can be used to improve the ram the exhaust can directly affect the fuel quantityeffect of the charge as it enters the cylinder but injected. The lambda sensor is described in moreonly if they coincide with the opening of the inlet detail in Chapter 6.
  • 150. 134 Advanced automotive fault diagnosisFigure 7.37 Catalytic convertor conversion rate – effect of lambda control A graph to show the effect of lambda control in the lambda window (0.97 to 1.03), which is theconjunction with a catalytic converter is shown in region in which the TWC is at its most efficient.Figure 7.37. The principle of operation is as fol-lows; the lambda sensor produces a voltage which 7.15.3 Engine managementis proportional to the oxygen content of the exhaustwhich is in turn proportional to the air fuel ratio. operationAt the ideal setting this voltage is about 450 mV. The combination of ignition and injection controlIf the voltage received by the ECU is below this has several advantages. The information receivedvalue (weak mixture) the quantity of fuel injected from various sensors is used for computing bothis increased slightly. If the signal voltage is above fuelling and ignition requirements. Perhaps morethe threshold (rich mixture) the fuel quantity is importantly ignition and injection are closelyreduced. This alteration in air fuel ratio must not be linked. The influence they have on each othertoo sudden as it could cause the engine to buck. To can be easily taken into account to ensure that theprevent this the ECU contains an integrator, which engine is working at its optimum, under all oper-changes the mixture over a period of time. ating conditions. Figure 7.38 shows the layout A delay also exists between the mixture for- and components of a common system.mation in the manifold and the measurement of Overall this type of system is less complicatedthe exhaust gas oxygen. This is due to the engine’s than separate fuel and ignition systems and inworking cycle and the speed of the inlet mixture, many cases the ECU is able to work in an emer-the time for the exhaust to reach the sensor and gency mode by substituting missing informationthe sensor’s response time. This is sometimes from sensors with pre-programmed values. Thisknown as dead time and can be as much as one will allow limited but continued operation in thesecond at idle speed but only a few hundred milli- event of certain system failures.seconds at higher engine speeds. The ignition system is integrated and is oper- Due to the dead time the mixture cannot be ated without a high tension (HT) distributor. Thecontrolled to an exact value of lambda equals one. ignition process is controlled digitally by theIf the integrator is adjusted to allow for engine ECU. The data for the ideal characteristics arespeed then it is possible to keep the mixture in stored in ROM from information gathered during
  • 151. Engine systems 135Figure 7.38 Engine management – Motronicboth prototyping and development of the engine. 12° gap positioned 114° before top dead centreThe main parameters for ignition advance are (BTDC) for number 1 cylinder. The signal pro-engine speed and load but greater accuracy can be duced by the flywheel sensor is essentially a sineachieved by taking further parameters into account wave with a cycle missing corresponding to the gapsuch as engine temperature. This provides both in the teeth of the reluctor plate. The informationoptimum output and close control of anti-pollution provided to the ECU is engine speed from the fre-levels. Performance and pollution level control quency of the signal and engine position from themeans that the actual ignition point must be in number of pulses before or after the missed pulses.many cases a trade off between the two. The basic ignition advance angle is obtained The injection system is multipoint and, as is from a memorised cartographic map. This is heldthe case for all fuel systems, the amount of fuel in a ROM chip within the ECU. The parametersdelivered is primarily determined by the amount for this are:of air ‘drawn’ into the engine. The method for ● engine rev/min given by the flywheel sensor;measuring this data is indirect in the case of this ● inlet air pressure given by the MAP sensor.system as a pressure sensor is used to determinethe air quantity. The above two parameters (speed and load) give Electromagnetic injectors control fuel supply the basic setting but to ensure optimum advanceinto the engine. The injector open period is deter- angle the timing is corrected by:mined by the ECU. This will obtain very accurate ● coolant temperaturecontrol of the air fuel mixture under all operating ● air temperatureconditions of the engine. The data for this is stored ● throttle butterfly positionin ROM in the same way as for the ignition. The main source of reference for the ignition The ignition is set to a predetermined advancesystem is from the crankshaft position sensor. This during the starting phase. Figure 7.39 shows ais a magnetic inductive pick up sensor positioned typical advance, fuelling and other maps used bynext to a flywheel ring containing 58 teeth. Each the Motronic system. This data is held in ROM.tooth takes up a 6° angle of the flywheel with one For full ignition control, the ECU has to first
  • 152. 136 Advanced automotive fault diagnosis Ignition angle ● Partial throttle is the main area of control and, Part load as already stated, the basic timing is set ini- Full load Trailing tially by a programme as a function of engine throttle speed and manifold pressure. Corrections are the added according to: Load gine speed Cranking Idle En ● operational strategy ● knock protection Inverse Lambda factor ● phase correction Full load Part load Overrun The ECU will also control ignition timing vari- fuel cut off ation during overrun fuel cut off and reinstate- ment and also to ensure anti-jerk control. When speed starting the ignition timing plan is replaced by a Load ngine Idle E specific starting strategy. Phase correction is when EGR valve position the ECU adjusts the timing to take into account the time taken for the HT pulse to reach the spark plugs. To ensure good driveability the ECU can limit the variations between the two ignition sys- ed tems to a maximum value, which varies according Load e spe Engin to engine speed and the basic injection period. Dwell angle An anti jerk function operates when the basic injection period is less than 2.5 ms and the engine speed is between 720 and 3200 rev/min. This func- tion operates to correct the programmed ignition timing in relation to the instantaneous engine ed spe speed and a set filtered speed. This is done to sta- Battery voltage ine Eng bilise the engine rotational characteristics as much Opening ratio (air bypass) as possible. In order to maintain constant energy HT the dwell period must increase in line with engine speed. So that the ignition primary current reaches its maximum at the point of ignition the ECU con- Engin e tem pera e sp eed trols the dwell by use of another memory map, ture Engin which takes battery voltage into account. Transition compensation Fuel is collected from the tank by a pump either immersed in it or outside, but near the tank. The immersed type is quieter in operation and has better cooling and no internal leaks. The fuel is directed forwards to the fuel rail or mani- fold, via a paper filter. ed Fuel pressure is maintained at about 2.5 bar Load spe ine Eng above manifold pressure by a regulator mountedFigure 7.39 Motronic control maps (samples) on the fuel rail. Excess fuel is returned to the tank. The fuel is usually picked up via a swirl pot in the tank to prevent aeration of the fuel. Each ofdetermine the basic timing for three different the four inlet manifold tracts has its own injector.conditions. The fuel pump is a high pressure type and is a● Under idling conditions ignition timing is often two stage device: a low pressure stage created by moved very quickly by the ECU in order to con- a turbine drawing fuel from the tank; and a high trol idle speed. When timing is advanced engine pressure stage created by a gear pump delivering speed will increase within certain limits. fuel to the filter. It is powered by a 12 V supply● Full load conditions require careful control of from the fuel pump relay, which is controlled by ignition timing to prevent combustion knock. the ECU as a safety measure. When a full load signal is sensed by the ECU The rotation of the turbine draws fuel in via (high manifold pressure) the ignition advance the inlet. The fuel passes through the turbine and angle is reduced. enters the pump housing where it is pressurised
  • 153. Engine systems 137 The purpose of the fuel pressure regulator is to maintain differential pressure across the injectors at a predetermined constant. This means the regu- lator must adjust the fuel pressure in response to changes in manifold pressure. It is made of two compressed cases containing a diaphragm, a spring and a valve. The calibration of the regulator valve is deter- mined by the spring tension. Changes in manifold pressure vary the basic setting. When the fuel pressure is sufficient to move the diaphragm, the valve opens and allows fuel to return to the tank. The decrease in pressure in the manifold, also act- ing on the diaphragm at say idle speed, will allow the valve to open more easily, hence maintainingFigure 7.40 Roller cell fuel pump a constant differential pressure between the fuel rail and the inlet manifold. This is a constant acrossby rotation of the pump and the reduction of the the injectors and hence the quantity of fuel injectedvolume in the gear chambers. This pressure opens is determined only by the open time of the injec-a residual valve and fuel passes to the filter. tors. The differential pressure is maintained atWhen the pump stops, pressure is maintained by about 2.5 bar.this valve, which prevents the fuel returning. If, The air supply circuit will vary considerablydue to a faulty regulator or a blockage in the line, between manufacturers but an individual mani-fuel pressure rises above 7 bar an over pressure fold from a collector housing, into which the airvalve will open releasing fuel back to the tank. is fed via a simple butterfly, essentially suppliesFigure 7.40 shows this type of pump. each cylinder. The air is supplied from a suitable The fuel filter is placed between the fuel pump filter. A supplementary air circuit is utilised dur-and the fuel rail. It is fitted one way only to ensure ing the warm-up period after a cold start and tothat the outlet screen traps any paper particles control idle speed.from the filter element. The filter will stop con-tamination down to between 8 and 10 microns. 7.15.4 Gasoline directReplacement varies between manufacturers but injection (GDI)80 000 km (50 000 miles) is often recommended. The fuel rail, in addition to providing a uniform High-pressure injection systems for petrol/gas-supply to the injectors, acts as an accumulator. oline engines is based on a pressure reservoir andDepending on the size of the fuel rail some sys- a fuel rail, which a high-pressure pump chargestems also use an extra accumulator. The volume of to a regulated pressure of up to 120 bar. The fuelthe fuel rail is large enough to act as a pressure can therefore be injected directly into the com-fluctuation damper ensuring that all injectors are bustion chamber via electromagnetic injectors.supplied with fuel at a constant pressure. The air mass drawn in can be adjusted through Multipoint systems use one injector for each the electronically controlled throttle valve and iscylinder although very high performance vehicles measured with the help of an air-mass meter. Formay use two. The injectors are connected to the mixture control, a wide-band oxygen sensor isfuel rail by a rubber seal. The injector is an elec- used in the exhaust, before the catalytic converters.trically operated valve manufactured to a very This sensor can measure a range between a lambdahigh precision. The injector comprises a body and value of 0.8 and infinity. The engine electronicneedle attached to a magnetic core. When the control unit regulates the operating modes of thewinding in the injector housing is energised the engine with gasoline direct injection in three ways.core or armature is attracted and the valve opens 1. Stratified charge operation – with lambda val-compressing a return spring. The fuel is delivered ues greater than 1.in a fine spray to wait behind the closed inlet 2. Homogeneous operation – at lambda ϭ 1.valve until the induction stroke begins. Providing 3. Rich homogeneous operation – with lambdathe pressure across the injector remains constant ϭ 0.8.the quantity of fuel admitted is related to the openperiod, which in turn is determined by the time Compared to the traditional manifold injectionthe electromagnetic circuit is energised. system, the Bosch DI-Motronic must inject the
  • 154. 138 Advanced automotive fault diagnosis Figure 7.41 GDI system showing the main components (Source: Bosch Press) operation, the lambda value in the combustion chamber is between about 1.5 and 3. In the part- load range, gasoline direct injection achieves the greatest fuel savings with up to 40% at idle com- pared to conventional petrol injection processes. With increasing engine load, and therefore increas- ing injection quantities, the stratified charge cloud becomes even richer and emission characteristics become worse. Because soot may form under these conditions, the DI-Motronic engine control converts to a homo- geneous cylinder charge at a pre-defined engine load. The system injects very early during theFigure 7.42 Atomization in a GDI engine (Source: Bosch Press) intake process in order to achieve a good mixture of fuel and air at a ratio of lambda ϭ 1. As is the caseentire fuel amount in full-load operation in a for conventional manifold injection systems, thequarter of the time. The available time is signifi- amount of air drawn in for all operating modes, iscantly shorter during stratified charge operation adjusted through the throttle valve according toin part-load. Especially at idle, injection times of the desired torque specified by the driver.less than 0.5 ms are required due to the lower fuel Diagnosing faults with a GDI system is littleconsumption (Figure 7.41). This is only one-fifth different from the manifold injection types. Extraof the available time for manifold injection. care is needed because of the higher fuel pressures The fuel must be atomised very finely in order to of course. Injector waveforms can be checked ascreate an optimal mixture in the brief moment can those associated with the other sensors andbetween injection and ignition (Figure 7.42). The actuators.fuel droplets for direct injection are on averagesmaller than 20 ␮m. This is only one-fifth of thedroplet size reached with the traditional manifold 7.16 Diagnostics –injection and one-third of the diameter of a singlehuman hair. This improves efficiency considerably. combined injection and Direct injection engines operate according to fuel control systemsthe stratified charge concept in the part-load rangeand function with high excess air. In return, verylow fuel consumption is achieved. 7.16.1 Testing procedure The engine operates with an almost completely Warningopened throttle valve, which avoids additional Caution/Achtung/Attention – burning fuel canalternating charge losses. With stratified charge seriously damage your health!
  • 155. Engine systems 139 Engine management system diagnostic chart Start Hand and eye checks (loose wires, loose switches and other faults such as No MIL off and filters) – all connections clean system ok? and tight. Check battery – must Yes be 70% charged Yes Follow route identified by DTC available? the DTC – check sensor, actuator or wiring as No appropriate Spark at plug? Yes No Fuel Spark from pressure is coil? correct? No Yes No Yes If no spark or it will only Supply voltage to pump Is injector operation ok – jump a short distance If good spark then check (within 0.5 V battery – pump (suitable spray pattern or continue with this HT system for tracking and or regulator fault if supply dwell reading across procedure (colour of spark open circuits is ok) injector supply) is not relevant) Check pump relay and Check supply circuits from Check continuity of coil Check plug condition (leads circuit (note in most cases main relay (battery volts windings (primary 0.5 to 3 should be a maximum the ECU closes the relay minimum) ohms, secondary several resistance of about 30 k/m) but this may be bypassed k ohms) on cranking) Ensure all connections Continuity of injector wiring Supply and earth to (electrical and fuel are (0 ohms) Check continuity ‘module’ (12 V minimum of windings – (note that Check/replace plugs remade correctly) – return supply, earth drop 0.5 V to earlier stage if necessary many injectors are maximum) connected in parallel) Sensor readings and Supply to pulse generator if continuity of wiring (0 ohms appropriate (5 or 10 to 12 V). for the wiring sensors will Output of pulse generator vary with type) (inductive 1 V AC cranking, Hall 0 V to 8 V DC) If no fuel is being injected and all tests so far are ok Continuity of LT wires then suspect ECU (0 ohms) Replace ‘module’ but only if all tests above are satisfactory End Warning 7.16.2 Combined injection and Caution/Achtung/Attention – high voltages can fuel control fault diagnosis table seriously damage your health! Symptom Possible faultThe following procedure is very generic but with Engine will not Engine and battery earth connectionsa little adaptation can be applied to any system. start Fuel filter and fuel pumpRefer to manufacturer’s recommendations if in Air intake system for leaksany doubt. Fuses/fuel pump/system relays
  • 156. 140 Advanced automotive fault diagnosis Fuel injection system wiring and connections Fuel pressure regulator and delivery rate Coolant temperature sensor Air-mass meter Auxiliary air valve/idle speed control valve ECU and connector Fuel pressure regulator and delivery rate Limp home function – if fitted ECU and connector Hesitation Engine and battery earth connections Limp home function – if fitted at constant Throttle linkageEngine Engine and battery earth connections speed Vacuum hoses for leaksdifficult to Fuel injection system wiring and connections Auxiliary air valve/idle speed control valvestart when Fuses/fuel pump/system relays Fuel lines for blockage, fuel filter and fuel pumpcold Fuel filter and fuel pump Injector valves Air intake system for leaks ECU and connector Coolant temperature sensor Limp home function – if fitted Auxiliary air valve/idle speed control valve Hesitation Air intake system for leaks Fuel pressure regulator and delivery rate on overrun Fuel injection system wiring and connections ECU and connector Coolant temperature sensor Limp home function – if fitted Throttle potentiometerEngine Engine and battery earth connections Fuses/fuel pump/system relaysdifficult to Fuses/fuel pump/system relays Air sensor filterstart when Fuel filter and fuel pump Injector valveswarm Air intake system for leaks Air-mass meter Coolant temperature sensor Knock Knock control – if fitted Fuel injection system wiring and connections during Fuel injection system wiring and connections Air-mass meter acceleration Air-mass meter Fuel pressure regulator and delivery rate ECU and connector Air sensor filter Poor engine Engine and battery earth connections ECU and connector response Air intake system for leaks Knock control – if fitted Fuel injection system wiring and connectionsEngine starts Engine and battery earth connections Throttle linkagethen stops Fuel filter and fuel pump Coolant temperature sensor Air intake system for leaks Fuel pressure regulator and delivery rate Fuses/fuel pump/system relays Air-mass meter Idle speed and CO content ECU and connector Throttle potentiometer Limp home function – if fitted Coolant temperature sensor Excessive Engine and battery earth connections Fuel injection system wiring and connections fuel Idle speed and CO content ECU and connector consumption Throttle potentiometer Limp home function – if fitted Throttle valve/housing/sticking/initial positionErratic idling Engine and battery earth connections Fuel pressure regulator and delivery ratespeed Air intake system for leaks Coolant temperature sensor Auxiliary air valve/idle speed control valve Air-mass meter Idle speed and CO content Limp home function – if fitted Fuel injection system wiring and connections CO level Limp home function – if fitted Coolant temperature sensor too high ECU and connector Knock control – if fitted Emission control and EGR valve – if fitted Air-mass meter Fuel injection system wiring and connections Fuel pressure regulator and delivery rate Air intake system for leaks ECU and connector Coolant temperature sensor Limp home function – if fitted Fuel pressure regulator and delivery rateIncorrect Air intake system for leaks CO level Engine and battery earth connectionsidle speed Vacuum hoses for leaks too low Air intake system for leaks Auxiliary air valve/idle speed control valve Idle speed and CO content Idle speed and CO content Coolant temperature sensor Coolant temperature sensor Fuel injection system wiring and connectionsMisfire at Engine and battery earth connections Injector valvesidle speed Air intake system for leaks ECU and connector Fuel injection system wiring and connections Limp home function – if fitted Coolant temperature sensor Air-mass meter Fuel pressure regulator and delivery rate Fuel pressure regulator and delivery rate Air-mass meter Poor Engine and battery earth connections Fuses/fuel pump/system relays performance Air intake system for leaksMisfire at Air flow sensor Throttle valve/housing/sticking/initial positionconstant Fuel injection system wiring and connectionsspeed Coolant temperature sensor Fuel pressure regulator/fuel pressure andHesitation Engine and battery earth connections delivery ratewhen Air intake system for leaks Air-mass meteraccelerating Fuel injection system wiring and connections ECU and connector Vacuum hoses for leaks Limp home function – if fitted Coolant temperature sensor
  • 157. Engine systems 141 Figure 7.43 Air flow meter under test7.16.3 On-board diagnostics intake pressure sensor and a valve are needed to(OBD) control the activated charcoal filter to reduce and monitor evaporative emissions from the fuel tank.Figure 7.44 shows the Bosch Motronic M5 with A differential pressure sensor also monitors thethe OBD2 system. On-board diagnostics are fuel tank permeability. Besides the driver’s faultbecoming essential for the longer term operation lamp a considerable increase in the electronicsof a system for it to produce a clean exhaust. is required in the control unit in order to operateMany countries now require a very comprehen- this system. For more information on OBD,sive diagnosis of all components in the system please refer to Chapter 6.which affect the exhaust. Any fault detected willbe indicated to the driver by a warning light.OBD2 is intended to standardise the many varying 7.16.4 Fuel pump testingmethods used by different manufacturers. EOBD Typical high-pressure fuel pump characteris-is the European version; however, it is also thought tics are:that an extension to total vehicle diagnosticsthrough a common interface is possible in the ● delivery 120 litres per hour (1 litre in 30 s)near future. at 3 bar; Digital electronics allow both sensors and actu- ● resistance 0.8 ⍀ (static);ators to be monitored. Allocating values to all ● voltage 12 V;operating states of the sensors and actuators does ● current 10.5 A.this. If a deviation from these figures is detectedthis is stored in memory and can be output in the An ideal test for a fuel pump is its delivery.workshop to assist with faultfinding. Using a suitable measuring receptacle, bypass Monitoring of the ignition system is very impor- the pump relay and check the quantity of fueltant as misfiring not only produces more emis- delivered in a set time (refer to manufacturer’ssions of hydrocarbons but the unburned fuel enters specifications). A reduced amount would indi-the catalytic converter and burns there. This can cate either a fuel blockage, a reduced electricalcause higher than normal temperatures and may supply to the pump or an inefficient pump.damage the catalytic converter. An accurate crankshaft speed sensor is used tomonitor ignition and combustion in the cylin- 7.16.5 Injector testingders. Misfiring alters the torque of the crankshaft Injectors typically have the characteristics asfor an instant, which causes irregular rotation. listed:This allows a misfire to be recognised instantly. A number of further sensors are required for ● supply voltage 12 V;the OBD2 functions. Another lambda sensor after ● resistance 16 ⍀;the catalytic converter monitors its operation. An ● static output 150 cc per minute at 3 bar.
  • 158. 142 Advanced automotive fault diagnosis Activated charcoal container Secondary Pressure adjuster air pump Fuel pressure controller Ignition coil Tank Isolating valve airbleed Intake pipe valve pressure Phase Air mass flow meter sensor sensor Secondary Injection valve air valve Knock Tempe- Air sensor Fuel rature temp. filter sensor sensor Idle Lambda running sensor Exhaust adjustor return valve Engine rev/min sensor Lambda Differential sensor pressure Diagnostic interface sensor Diagnostic lamp Electric Car body acceleration sensor fuel pumpFigure 7.44 Motronic M5 with OBD II. Bosch press photo
  • 159. Engine systems 143Resistance checks (with the supply disconnected) 7.17 Engine managementare an ideal start to testing injectors. Further testswith the fuel pressurised by the pump and each and faultfindinginjector in turn held in a suitable receptacle, informationinclude:● spray pattern usually a nice cone shape 7.17.1 Diagnostic charts with good atomisation; ‘Autodata’ supply diagnostic charts specific to● delivery set quantity over a set time; particular management systems. Figure 7.45 is a● leakage any more than two drops a minute typical example. Note that some boxes refer you is considered excessive (zero is desirable). to a further publication.Figure 7.45 Bosch Mono-Jetronic (single point injection) (Source: Autodata)
  • 160. 144 Advanced automotive fault diagnosis7.17.2 Circuit diagrams 7.18 Air supply andCircuit diagrams can be printed out from some exhaust systems‘Workshop manual CDs’. Figure 7.46 is an exam-ple of this. 7.18.1 Exhaust system A vehicle exhaust system directs combustion products away from the passenger compartment,7.17.3 Component testing data reduces combustion noise and, on most modernFigure 7.47 is a printout from a CD, showing vehicles, reduces harmful pollutants in thewhat data is available for testing a specific exhaust stream. The main parts of the systemcomponent. are the exhaust manifold, the silencer or muffler,Figure 7.46 Engine management circuit diagram
  • 161. Engine systems 145the pipes connecting them, and a catalytic- allow movement because the engine is also rubberconverter. mounted, and they also reduce vibration noise. Most exhaust systems are made from mild An exhaust manifold links the engine exhauststeel, but some are made from stainless steel ports to the down pipe and main system. It alsowhich lasts much longer. The system is suspended reduces combustion noise and transfers heat down-under the vehicle on rubber mountings. These stream to allow the continued burning of hydro- carbons and carbon monoxide. The manifold is connected to the down pipe, which in turn can be connected to the catalytic converter. Most exhaust manifolds are made from cast iron, as this has the necessary strength and heat transfer properties. The silencer’s main function is to reduce engine noise to an acceptable level. Engine noise is a mixed up collection of its firing frequencies (the number of times per second each cylinder fires). These range from about 100 to 400 Hz (cycles/ sec). A silencer reduces noise in two main ways: ● interior chambers using baffles, which are tuned to set up cancelling vibrations; ● absorptive surfaces function like sound- deadening wall and ceiling panels to absorb noise. When the exhaust gases finally leave the exhaust system, their temperature, pressure and noise have been reduced considerably. The over- all length of an exhaust system including the silencers can affect the smooth flow of gases. For this reason do not alter the length or change the layout of an exhaust system. Figure 7.48 shows aFigure 7.47 Testing data silencer/muffler box. Figure 7.48 Exhaust noise reduction methods
  • 162. 146 Advanced automotive fault diagnosis7.18.2 Catalytic converters The core has traditionally been made from ceramic of magnesium aluminium silicate. DueStringent regulations in most parts of the world to the several thousand very small channels, thishave made the use of a catalytic converter neces- provides a large surface area. It is coated withsary. The three-way catalyst (TWC) is used to a wash coat of aluminium oxide, which againgreat effect by most manufacturers. It is in effect increases its effective surface area by about sev-a very simple device; it looks similar to a stand- eral thousand times. ‘Noble’ metals are used forard exhaust silencer box. Note that in order for the catalysts. Platinum helps to burn off thethe ‘cat’ to operate correctly, the engine must be hydrocarbons (HC) and carbon monoxide (CO),always well tuned. This is to ensure that the right and rhodium helps in the reduction of nitrogen‘ingredients’ are available for the catalyst to oxides (NOx). The whole three-way catalytic con-perform its function. A catalytic converter works verter only contains about three to four grams ofby converting the dangerous exhaust gases into these precious metals. Some converters now usegases which are non-toxic. metal cores (substrates). Figure 7.49 shows the e xid n dio oge on nitr carb ater N2 O 2 w C H2O des oxi de gen i n itro onox NOx bon m car bo n CO rocar hy d HCDuring the catalytic conversion become carbon dioxideof exhaust pollutants and water (steam) throughinto environmentally compatible oxidation whereas nitrogencomponents carbon monoxide is produced from nitrogenand hydrocarbon oxides through reduction.Lambda sensor controlled mixtureSince the NOx emissions behave contrarily to Precious metalthe CO+HC values the exhaust gas purificationcannot start from the respective minimum. Thesmallest common denominator lies at the stoi-chiometric airfuel ratio of 14.7:1, the lambda Washcoatwindow. An oxygen sensor in the exhaust flow,the lambda sensor, controls the optimum mix- NOxture via control electronics, thus ensuring this COoptimum in all engine load cases. HC Ceramic carrier Top: the structure of Below: the active catalytic Conversion λ-window a ceramic monolith layer in the exhaust gas flow [%] 100 CO 90 NOx HC 80 70 60 50 40 30 20 Since pollutants behave 10 very differently in the exhaust flow the common 0.925 0.95 0.975 1.0 1.025 1.05 1.075 optimum has to be determined rich Stoichiometric lean for conversion: this is λ lambda = 1. Figure 7.49 Catalytic converter operation
  • 163. Engine systems 147operation of a catalytic converter and how the modern low styled bonnets. Because it can belambda window is important. cleaned and fresh oil added, an oil bath air cleaner The engine can damage a catalytic converter might still be used for vehicles operating in dustyin one of two ways: conditions. Air temperature control is used to help the● firstly by the use of leaded fuel which can vehicle conform to emission control regulations cause lead compounds to be deposited on the and for good driveability when the engine is cold. active surfaces; Good vaporisation of the fuel is the key. An auto-● secondly by engine misfire which can cause matic control is often fitted to make sure that the the catalytic converter to overheat due to air intake temperature is always correct. The air burning fuel inside the unit. cleaner has two intake pipes, one for cold air andSome manufacturers use a system on some vehicles the other for hot air from the exhaust manifold orwhere a sensor checks the output of the ignition hot box. The proportion of hot and cold air is con-HT system and, if the spark is not present, will trolled by a flap, which is moved by a diaphragmnot allow fuel to be injected. Misfire detection is acted on by low pressure from the inlet manifold.also part of current on-board diagnostic (OBD) The flap rests in the hot air pick up position.legislation in some countries and future legisla- A thermo-valve in the air stream senses thetion in others. temperature of the air going into the engine. When a temperature of about 25°C is reached, the valve opens. This removes the connection to the7.18.3 Air supply system manifold, which in turn increases the pressureThere are three purposes of the complete air sup- acting on the diaphragm. The flap is now causedply system: to move and the pick up is now from the cool air position. The flap is constantly moving ensuring● clean the air; that the temperature of air entering the engine● control air temperature; remains constant. Picking up hot air when the● reduce noise. engine is still cold can also help to prevent icing A filter does the air cleaning and drawing air in a carburettor.from around the exhaust manifold helps to controlair temperature. When large quantities of air aredrawn into the engine it causes the air to vibrate 7.19 Diagnostics – exhaustand this makes it noisy. In the same way as with theexhaust system, baffles are used to stop resonance. and air supplyResonance means that when vibrations reach a nat-ural level they tend to increase and keep going. A 7.19.1 Systematic testinggood example of how much noise is reduced by the If the reported fault is a noisy exhaust proceed asair intake system is to compare the noise when an follows.engine is run with the air filter removed. Two types of air filter are in use, the first of 1. Check if the noise is due to the exhaust knock-these being by far the most popular: ing or blowing. 2. Examine the vehicle on the lift.● paper element; 3. Are further tests required or is it obvious?● oil bath and mesh. 4. Cover the end of the exhaust pipe with a ragThe paper element is made of resin-impregnated for a second or two to highlight where thepaper. Air filters using this type of replaceable exhaust may be blowing.element are used both for car and commercial 5. Renew the exhaust section or complete sys-vehicles. They provide a very high filtering tem as appropriate.efficiency and reasonable service life. They can 6. Run and test for leaks and knocking.be mounted in any position available under thebonnet. Service intervals vary so check recom-mendations. 7.19.2 Test results The oil bath and mesh type of air cleaner was Some of the information you may have to getwidely used on non-turbo charged commercial from other sources such as data books or a work-vehicles. However, it is not very practical for shop manual is listed in the following table.
  • 164. 148 Advanced automotive fault diagnosis to restrict the movement of air. When the engineTest carried out Information required reaches its operating temperature the flap opensAir filter condition Clearly a physical examination but note and allows the air to flow over the engine. The the required service intervals cooling fan is a large device and is driven from theExhaust noise An idea of the normal noise level – engine by a belt. This belt must not be allowed to note that ‘big bore’ exhausts will make slip or break, because serious damage will occur. more noise than the ‘correct’ type Car heating is not easy to arrange with an air- cooled engine. Some vehicles use a heat exchanger7.19.3 Exhaust and air supply around the exhaust pipe. Air is passed throughfault diagnosis table I this device where it is warmed. It can then be used for demisting and heating with the aid of anSymptom Possible faults Suggested action electric motor and fan.Exhaust noise Hole in pipe, box Renew as appropriate or at joints 7.20.2 Water cooled systemKnocking noise Exhaust incorrectly Reposition The main parts of a water cooled system are as positioned Broken mountings Renew follows:Rich mixture/ Blocked air filter Replace ● water jacket;smoke ● water pump;Noisy air intake Intake trunking or Repair or secure as ● thermostat; filter box leaking required ● radiator; or loose ● cooling fan.Poor cold Hot air pick up not Check pipedriveability operating connections to inlet Water-cooled engines work on the principle of manifold for leaks. surrounding the hot areas inside the engine with Renew temperature a water jacket. The water takes on heat from the valve or actuator engine and, as it circulates through the radiator, gives it off to atmosphere. The heat concentra-7.19.4 Exhaust fault diagnosis tion around the top of the engine means a watertable 2 pump is needed to ensure proper circulation. The water pump circulates water through theSymptom Possible cause radiator and around the engine when the thermo- stat is open. Water circulates only round the engineExcessive noise Leaking exhaust system or manifold joints when the thermostat is closed and not through Hole in exhaust system the radiator. Forcing water around the engineExcessive fumes Leaking exhaust system or manifold jointsin car prevents vapour pockets forming in very hot areas. This circulation is assisted by the thermo-Rattling noise Incorrect fitting of exhaust system Broken exhaust mountings siphon action. The thermo-siphon action causes Engine mountings worn the water to circulate because as the water is heated it rises and moves to the top of the radi- ator. This pushes down on the colder water under-7.20 Cooling neath which moves into the engine. This water is heated, rises and so on. Coolant from the engine water jacket passes7.20.1 Air-cooled system through a hose to the radiator at the top. It thenAir-cooled engines with multi-cylinders, espe- passes through thin pipes called the radiatorcially under a bonnet, must have some form of fan matrix to the lower tank and then back to thecooling and ducting. This is to make sure all cylin- lower part of the engine.ders are cooled evenly. The cylinders and cylinder Many water passages between the top andheads are finned. Hotter areas, such as near the bottom tanks of the radiator are used, to increaseexhaust ports on the cylinders, have bigger fins. the surface area. Fins further increase the surface Fan-blown air is directed by a metal cowling so area to make the radiator even more efficient. Ait stays close to the finned areas. A thermostatic- cooling fan assists air flow. The heat from theally controlled flap will control airflow. When the coolant passes to the pipes and fins and then toengine is warming up, the flap will be closed the air as it is blown by a fan over the fins.
  • 165. Engine systems 149 Many modern radiators are made from alu- 7.20.3 Sealed and semi-sealedminium pipes and fins with plastic tanks top and systemsbottom (down flow), or at each end (cross flow).The cross flow radiators with tanks at each end Cooling systems on most vehicles today are sealedare becoming the most popular. The more trad- or semi-sealed. This allows them to operate atitional method was to use copper and brass. pressures as much as 100 N/m2 (100 Pascal) over A thermostat is a temperature controlled valve. atmospheric pressure, raising the boiling point ofIts purpose is to allow coolant to heat up more the coolant to as much as 126.6°C (rememberquickly and then be kept at a constant temperature. water boils at 100°C at atmospheric pressure). TheThe total coolant volume in an engine takes time to system can therefore operate at a higher tempera-heat up. Modern engines run more efficiently when ture and with greater efficiency.at the correct operating temperature. The action of The pressure buildup is made possible by thethe thermostat is such as to prevent water circula- radiator pressure cap. The cap contains a pressuretion from the engine to the radiator, until a set tem- valve which opens at a set pressure, and a vacuumperature is reached. When the valve opens there is valve which opens at a set vacuum. On a semi-a full circuit for the coolant and a good cooling sealed system, air is pushed out to atmosphereaction occurs because of full flow through the radi- through the pressure valve as the coolant expands.ator. The constant action of the thermostat ensures Air is then drawn back into the radiator throughthat the engine temperature remains at a constant the vacuum valve as the coolant cools and con-level. The thermostat used by almost all modern tracts. A sealed system has an expansion tank intoengine is a wax capsule type. If the thermostat is which coolant is forced as it expands, and whenfaulty ensure that the correct type for the engine is the engine cools, coolant can flow from the tankfitted as some work at different temperatures. back into the cooling system. Figure 7.50 shows a The water pump is driven by a V-belt or multi semi-sealed type cooling system.V-belt from the crankshaft pulley or by the cam Correct levels in the expansion tank or in anbelt. The pump is a simple impeller type and is unsealed radiator are very important. If too muchusually fitted at the front of the engine (where the coolant is used it will be expelled on to the floorpulleys are). It assists with the thermo-siphon when the engine gets hot. If not enough is usedaction of the cooling system, forcing water around then the level could become low and overheatingthe engine block and radiator. could take place. The engine fan, which maintains the flow of airthrough the radiator, is mounted on the water-pump Warningpulley on older systems. Most cooling fans now are If a pressure cap is removed from a hot sys-electric. These are more efficient because they only tem, hot water under pressure will boil thework when needed. The forward motion of the car instant pressure is released. This can be veryalso helps the air movement through the radiator. dangerous. Figure 7.50 Semi-sealed cooling system
  • 166. 150 Advanced automotive fault diagnosis Heat from the engine can be used to increase 7.21.2 Test equipmentthe temperature of the car interior. This isachieved by use of a heat exchanger, often called Note: You should always refer to the manufac-the heater matrix. Due to the action of the thermo- turer’s instructions appropriate to the equip-stat in the engine cooling system the water tem- ment you are using.perature remains nearly constant. The air beingpassed over the heater matrix is therefore heated Cooling system pressure testerto a set level. (Figure 7.51) A source of hot air is now available for heat-ing the vehicle interior. Some form of control is This is a pump with a pressure gauge built in,required over how much heat is required. The together with suitable adapters for fitting to themethod used on most modern vehicles is blend- header tank or radiator filler. The system can thening. This is a control flap that determines how be pressurized to check for leaks. The pressuremuch of the air being passed into the vehicle is can be looked up or it is often stamped on the fillerdirected over the heater matrix. Some systems cap. A good way of doing this test is to pressuriseuse a valve to control the hot coolant flowing to the system when cold and then start the enginethe heater matrix. and allow it to warm up. You can be looking for By a suitable arrangement of flaps it is possible leaks but beware of rotating components.to direct air of the chosen temperature to selectedareas of the vehicle interior. In general, basic sys- Antifreeze testertems allow the warm air to be adjusted betweenthe inside of the windscreen and the driver and This piece of equipment is a hydrometer used topassenger footwells. Fresh cool air outlets with measure the relative density of the coolant. Thedirectional nozzles are also fitted. relative density of coolant varies with the amount One final facility, which is available on many of antifreeze. A table can be used to determinevehicles, is the choice between fresh or recir- how much more antifreeze should be added to giveculated air. The primary reason for this is to the required protection.decrease the time taken to demist or defrost thevehicle windows and simply to heat the car inter- Temperature meter/thermometerior more quickly, and to a higher temperature. Sometimes the dashboard temperature gauge read-The other reason is that for example, in heavy ing too high can create the symptoms of an over-congested traffic, the outside air may not be very heating problem. A suitable meter or thermometerclean. can be used to check the temperature. Note though7.21 Diagnostics – cooling7.21.1 Systematic testingIf the reported fault is loss of coolant proceed asfollows.1. Check coolant level and discuss with cus- tomer how much is being lost.2. Run the engine to see if it is overheating.3. If the engine is not overheating a leak would seem to be most likely.4. Pressure test the cooling system and check for leaks from hoses, gaskets and the radiator.5. Renew a gasket or the radiator, clips or hoses as required. Top up the coolant and check antifreeze content.6. Road test the vehicle to confirm the fault is cured and that no other problems have occurred. Figure 7.51 Cooling system pressure tester
  • 167. Engine systems 151that normal operating temperature is often well Airlock in system (some systems have aabove 90°C (hot enough to burn badly). complex bleeding procedure) Pressure cap faulty Overcooling Thermostat stuck open Temperature gauge inaccurate7.21.3 Test results Cooling fan operating when not neededSome of the information you may have to get External coolant Loose or damaged hose leak Radiator leakfrom other sources such as data books or a work- Pressure cap seal faultyshop manual is listed in the following table. Water pump leak from seal or bearing Boiling due to overheating or faulty pressure capTest carried out Information required Core plug leakingLeakage test System pressure. Printed on the cap or Internal coolant Cylinder head gasket leaking from data books. About I bar is normal leak Cylinder head crackedAntifreeze content Cooling system capacity and required Corrosion Incorrect coolant (antifreeze, etc.) percentage of antifreeze. If the system Infrequent flushing holds six litres then for a 50% antifreeze Freezing Lack of antifreeze content you will need to add three litres Incorrect antifreeze of antifreeze. Don’t forget you will need to drain out three litres of water to make room for the antifreeze!Operating This is about the same as the thermostat 7.22 Lubricationtemperature opening temperature Ϫ 88 to 92°C is a typical range 7.22.1 Lubrication system From the sump reservoir under the crankshaft oil is7.21.4 Cooling fault diagnosis drawn through a strainer into the pump. Oil pumpstable I have an output of tens of litres per minute and operating pressures of over 5 bar at high speeds.Symptom Possible faults Suggested action A pressure relief valve limits the pressure of the lubrication system to between 2.5 and bar2. ThisOverheating Lack of coolant Top up but then control is needed because the pump would pro- check for leaks duce excessive pressure at high speeds. After leav- Thermostat stuck Renew closed ing the pump, oil passes into a filter and then into a Electric cooling fan Check operation of main oil gallery in the engine block or crankcase. not operating thermal switch Drillings connect the gallery to the crankshaft Blocked radiator Renew bearing housings and, when the engine is run- Water pump/fan Check, adjust/renew ning, oil is forced under pressure between the belt slipping rotating crank journals and the main bearings.Loss of coolant Leaks Pressure test when The crankshaft is drilled so that the oil supply cold and hot, look for leaks and repair from the main bearings is also to the big end as required bearing bases of the connecting rods.Engine does not Thermostat stuck in Renew The con-rods are often drilled near the base soreach normal the open position that a jet of oil sprays the cylinder walls and thetemperature or it underside of the pistons. In some cases the con-takes a long time rod may be drilled along its entire length so that oil from the big end bearing is taken directly to the gudgeon pin (small end). The surplus then7.21.5 Cooling fault diagnosis splashes out to cool the underside of the pistontable 2 and cylinder. The camshaft operates at half crankshaft speed,Symptom Possible cause but it still needs good lubrication because as the high pressure loads on the cams. It is usual toOverheating Low coolant level (maybe due to a leak) supply pressurised oil to the camshaft bearings Thermostat stuck closed Radiator core blocked and splash or spray oil on the cam lobes. On over- Cooling fan not operating head camshaft engines, two systems are used. In Temperature gauge inaccurate the simplest system the rotating cam lobes dip into
  • 168. 152 Advanced automotive fault diagnosisa trough of oil. Another method is to spray the oil pump. This is normally on the end of the oilcam lobes with oil. This is usually done by an oil pick-up pipe. An extra filter is also used that stopspipe with small holes in it alongside the camshaft. very fine particles. The most common type has aThe small holes in the side of the pipe aim a jet of folded, resin impregnated paper element. Pumpingoil at each rotating cam lobe. The surplus splashes oil through it removes all but smallest solidsover the valve assembly and then falls back into from the oil.the sump. Most engines use a full-flow system to filter On cars where a chain drives the cam, a small all of the oil after it leaves the pump. The mosttapping from the main oil gallery sprays oil on popular method is to pump the oil into a canisterthe chain as it moves past or the chain may sim- containing a cylindrical filter. From the innerply dip in the sump oil. Figure 7.52 shows a typ- walls of the canister, the oil flows through the fil-ical lubrication system. ter and out from the centre to the main oil gallery. Full-flow filtration works well provided the filter is renewed at regular intervals. If it is left in service7.22.2 Oil filters too long it may become blocked. When this hap-Even new engines can contain very small par- pens the buildup of pressure inside the filter forcesticles of metal left over from the manufacturing open a spring-loaded relief valve in the housingprocess or grains of sand which have not been and the oil bypasses the filter. This valve pre-removed from the crankcase after casting. Old vents engine failure, but the engine will be lubri-engines continually deposit tiny bits of metal cated with dirty oil until the filter is renewed. Thisworn from highly loaded components such as the is better than no oil!piston rings. To prevent any of these lodging in A bypass filtration system was used on olderbearings or blocking oil ways, the oil is filtered. vehicles. This system only filters a proportion of The primary filter is a wire mesh strainer that the oil pump output. The remainder is fed directlystops particles of dirt or swarf from entering the to the oil gallery. At first view this seems a strangeFigure 7.52 Lubrication system
  • 169. Engine systems 153idea but all of the oil does eventually get filtered. Crankase breathing or ventilation of the engineThe smaller amount through the filter allows a was first done by what is known as an open sys-higher degree of filtration. tem, but this has now been completely replaced by the closed system. The gases escaping from7.22.3 Oil pumps an engine with open crankcase ventilation as described above are very toxic. Legislation nowIn its simplest form an oil pump consists of two demands a positive closed system of ventilation.gear wheels meshed together in a tight space so This makes the pollution from cylinder blow-bythat oil cannot escape past the sides. The engine gases negligible. Positive crankcase ventilationdrives one wheel. As the gears rotate in opposite is the solution to this problem.directions, the gap between each tooth in each In early types of closed system crankcase ven-wheel traps a small quantity of oil from an inlet tilation, the lower pressure at the carburettor airport. The trapped oil is carried round by each cleaner was used to cause an airflow through thewheel towards an outlet port on the opposite side inside of the engine. The breather outlet was sim-where it is forced out by the meshing teeth. ply connected by a pipe to the air cleaner. This The principle of squeezing oil from an ever- caused the crankcase gases to be circulated anddecreasing space is also used in the rotor type then burned in the engine cylinders. A flame trappump. An inner and outer rotor are mounted on was included in the system, to prevent a crankcasedifferent axes in the same cylinder. The inner explosion if the engine backfired.rotor, which commonly has four lobes, is driven In modern closed systems the much lower pres-by the engine. It meshes with an outer rotor, which sure within the inlet manifold is used to extracthas five lobes. As they rotate, the spaces between crankcase gases. This has to be controlled in mostthem change size. The inlet port is at a point where cases by a variable regulator valve or pressure con-the space between the rotor lobes is increasing. scious valve (PCV). The valve is fitted between theThis draws the oil in to the pump. The oil is then breather outlet and the inlet manifold. It consists ofcarried round the pump. As rotation continues, the a spring-loaded plunger, which opens as the inletspace between the lobes gets smaller. This com- manifold pressure reduces. When the engine is sta-presses the oil out of the outlet port. tionary the valve is closed. Under normal running Oil pumps can produce more pressure than is conditions the valve opens to allow crankcaserequired. A valve is used to limit this pressure to gases to enter the inlet manifold with minimuma set value. The pressure relief valve is a simple restriction. At low manifold pressures during idlingdevice, which in most cases works on the ball and overrun (pressure is less than atmospheric),and spring principle. This means that when the further travel of the valve plunger against its springpressure on the ball is greater than the spring, the closes it in the opposite direction. This reduces gasball moves. The pressure relief valve is placed in flow to the inlet manifold. This feature makes surethe main gallery so that excess pressure is pre- that the fuel control process is not interfered withvented. When the ball moves oil is simply under these conditions. The valve also acts as areturned to the sump. safety device in case of a backfire. Any high pres- sure created in the inlet manifold will close the7.22.4 Crankcase ventilation – valve completely. This will isolate the crankcase and prevent the risk of explosion.engine breather systemsBreathing is very important; without being able tobreathe, we would die! It is almost as important 7.23 Diagnostics –for an engine breathing system to work correctly.There are two main reasons for engine breathers. lubrication● Prevent pressure buildup inside the engine 7.23.1 Systematic testing crankcase due to combustion gases blowing If the reported fault is that the oil pressure light past the pistons. The buildup of pressure will comes on at low speed proceed as follows. blow gaskets and seals but also there is a high risk of explosion. 1. Run the engine and see when the light goes off● Prevent toxic emissions from the engine. or comes on. Emission limits are now very strict, for good 2. Is the problem worse when the engine is hot? reason – our health! Check the oil level! When was it last serviced?
  • 170. 154 Advanced automotive fault diagnosis3. If oil level is correct then you must investigate 7.23.3 Test results further.4. Carry out an oil pressure test to measure the Some of the information you may have to get actual pressure. from other sources such as data books, or a work-5. If pressure is correct then renew the oil pres- shop manual is listed in the following table. sure switch. If not engine strip down is likely.6. Run and test for leaks. Test carried out Information required Oil pressure Oil pressure is measured in bars. A typical reading would be about 3 bar7.23.2 Test equipment Crankcase pressure By tradition pressures less than Note: You should always refer to the manufac- atmosphere are given in strange turer’s instructions appropriate to the equip- ways, such as inches of mercury or inches of water! This is why I like ment you are using. to stick to absolute pressure and the bar! Zero bar is no pressure,Oil pressure test gauge (Figure 7.53) I bar is atmospheric pressure and so on. Two to 3 bar is more thanThis is a simple pressure gauge that can be fitted atmospheric pressure like in awith suitable adapters into the oil pressure switch tyre. The trouble is standardshole. The engine is then run and the pressure vary so make sure you compare like with like! Back to crankcasereadings compared to data. pressure – it should be less than atmospheric, check dataVacuum gauge Oil condition Recommended type of lubricantA simple ‘U’ tube full of water is often used.This is connected to the oil dipstick tube and theengine is run. The gauge should show a pressure 7.23.4 Lubrication fault diagnosisless than atmospheric (a partial vacuum). This table Ichecks the operation of the crankcase ventilationsystem. Symptom Possible faults Suggested action Low oil Lack of oil Top up pressure Blocked filter Renew oil and filter Defective oil pump Renew after further tests Defective oil Adjust if possible pressure relief valve or renew High crankcase Blocked crankcase Clean or replace pressure breather Blocked hose Clean or renew hose Pressure blowing by Engine overhaul may pistons be required Loss of oil Worn piston rings Engine overhaul may be required Leaks Renew seals or gaskets 7.23.5 Lubrication fault diagnosis table 2 Symptom Possible cause Oil leaks Worn oil seal (check breather system) Gasket blown Cam or rocker cover loose Oil filter seal Blue smoke Piston rings Valve stem seals Head gasketFigure 7.53 Oil pressure gauge
  • 171. Engine systems 1557.24 Batteries from a microporous plastic insulate these plates from each other. The grids, connecting strips and the battery7.24.1 Safety posts are made from a lead alloy. For many yearsThe following points must be observed when this was lead antimony (PbSb) but this has nowworking with batteries: been largely replaced by lead calcium (PbCa). The newer materials cause less gassing of the● good ventilation electrolyte when the battery is fully charged. This● protective clothing has been one of the main reasons why sealed bat-● supply of water available (running water teries became feasible as water loss is consider- preferable) ably reduced.● first aid equipment available, including eyewash Modern batteries described as sealed do still● no smoking or naked lights permitted. have a small vent to stop the pressure buildup due to the very small amount of gassing. A fur- ther requirement of sealed batteries is accurate7.24.2 Lead-acid batteries control of charging voltage.Incremental changes over the years have madethe sealed and maintenance-free battery, now in 7.24.3 Battery ratingcommon use, very reliable and long lasting. This In simple terms the characteristics or rating of amay not always appear to be the case to some end particular battery are determined by how muchusers, but note that quality is often related to the current it can produce and how long it can sustainprice the customer pays. Many bottom of the this current. The rate at which a battery can pro-range cheap batteries with a 12 month guarantee duce current is determined by the speed of thewill last for 13 months! chemical reaction. This in turn is determined by The basic construction of a nominal 12 V a number of factors:lead-acid battery consists of six cells connectedin series. Each cell producing about 2 V is housed ● surface area of the plates;in an individual compartment within a polypropyl- ● temperature;ene or similar case. Figure 7.54 shows a cut- ● electrolyte strength;away battery with its main component parts. The ● current demanded.active material is held in grids or baskets to form The actual current supplied therefore deter-the positive and negative plates. Separators made mines the overall capacity of a battery. The rating Figure 7.54 Lead-acid battery
  • 172. 156 Advanced automotive fault diagnosisof a battery has to specify the current output and 7.25 Diagnosing batterythe time. faultsAmpere hour This is now seldom used but describescapacity how much current the battery is able to 7.25.1 Servicing batteries supply for either 10 or 20 hours. The 20-hour figure is the most common. For In use a battery requires very little attention other example, a battery quoted as being than the following when necessary. 44 Ah (ampere-hour) will be able, if fully charged, to supply 2.2 A for 20 hours ● Corrosion should be cleaned from terminals before being completely discharged (cell using hot water. voltage above 1.75 V) ● Terminals should be smeared with petroleumReserve capacity A system used now on all new batteries jelly or vaseline not ordinary grease. is reserve capacity. This is quoted as a ● Battery tops should be clean and dry. time in minutes for which the battery ● If not sealed, cells should be topped up with will supply 25 A at 25°C to a final voltage of 1.75 V per cell. This is used distilled water 3 mm above the plates. to give an indication of how long the ● Battery should be securely clamped in position. battery could run the car if the charging system was not working. Typically a 44 Ah battery will have a reserve capacity of about 60 minutes. 7.25.2 Maintenance-freeCold cranking amps Batteries are given a rating to indicate By far the majority of batteries now available are performance at high current output and classed as ‘maintenance-free’. This implies that at low temperature. A typical value of little attention is required during the life of the 170 A means that the battery will supply this current for one minute at a battery. Earlier batteries and some heavier types temperature of Ϫ18°C at which point do, however, still require the electrolyte level to the cell voltage will fall to 1.4 V (BS). be checked and topped up periodically. Battery posts are still a little prone to corrosion and hence the usual service of cleaning with hot water ifThese cold cranking amps (CCA) capacity rating appropriate and the application of petroleum jellymethods do vary to some extent: British standards, or proprietary terminal grease is still recom-DIN standards and SAE standards are the three mended. Ensuring that the battery case and inmain examples! particular the top remains clean will help to reduce the rate of self-discharge.● BS 60 seconds The state of charge of a battery is still very● DIN 30 seconds important and in general it is not advisable to● SAE 30 seconds allow the state of charge to fall below 70% for long periods as the sulphate on the plates can In summary, the capacity of a battery is the harden, making recharging difficult. If a batteryamount of electrical energy that can be obtained is to be stored for a long period (more than a fewfrom it. It is usually given in ampere-hours, reserve weeks), then it must be recharged every so oftencapacity (RC) and cold cranking amps. to prevent it from becoming sulphated. Recom- mendations vary but a recharge every six weeks● A 40 Ah battery means it should give 2 A for is a reasonable suggestion. 20 hours.● The reserve capacity indicates the time in min- utes for which the battery will supply 25 A at 7.25.3 Charging 25°C.● Cold cranking current indicates the maximum The recharging recommendations of battery manu- battery current at Ϫ18°C (0°F) for a set time facturers vary slightly. The following methods, (standards vary). however, are reasonably compatible and should not cause any problems. The efficiency of a bat- A battery for normal light vehicle use may be tery is not 100%. Therefore the recharging processrated as follows: 44 Ah, 60 RC and 170 A CCA must ‘put back’ the same Ah capacity as was used(BS). A ‘heavy duty’ battery will have the same on discharge plus a bit more to allow for losses.Ah rating as its ‘standard duty’ counterpart, but it It is therefore clear that the main question aboutwill have a higher CCA and RC. charging is not how much, but at what rate.
  • 173. Engine systems 157 The old recommendation was that the battery the buildup of pressure. A rate of about five timesshould be charged at a tenth of its Ah capacity for the ‘normal’ charge setting will bring the battery toabout 10 hours or less. This is assuming that the 70–80% of its full capacity within approximatelyAh capacity is quoted at the twenty hour rate, as one hour. The table below summarises the charg-a tenth of this figure will make allowance for the ing techniques for a lead-acid battery. Figures 7.55charge factor. This figure is still valid but as Ah and 7.56 show two typical battery chargers.capacity is not always used nowadays, a differentmethod of deciding the rate is necessary. One way Charging method Notesis to set a rate at a sixteenth of the reserve capacity,again for up to 10 hours. The final suggestion is Constant voltage Will recharge any battery in seven hours or less without any risk of overchargingto set a charge rate at one fortieth of the cold start (14.4 V maximum)performance figure, also for up to 10 hours. Constant current Ideal charge rate can be estimated as:Clearly if a battery is already half charged, half 1/10 of Ah capacity, 1/16 of RC or 1/40the time is required to recharge to full capacity. of cold start current (charge time of 10 In summary the ideal charge rate is determined to 12 hours or pro rata original state) Boost charging At no more than five times the idealfrom: rate, a battery can be brought up to● 1/10 of the Ah capacity; about 70% of charge in about one hour● 1/16 of the RC;● 1/40 of the CCA. 7.25.4 Battery faults The above suggested charge rates are to be rec- Any electrical device can suffer from two mainommended as the best way to prolong battery life. faults; open circuit or short circuit. A battery is noThey do all, however, imply a constant current exception but it can also suffer from other prob-charging source. A constant voltage charging sys- lems such as low charge or low capacity. Often atem is often the best way to charge a battery. This problem which seems to be with a vehicle batteryimplies that the charger, an alternator on a car for can be traced to another part of the vehicle suchexample, is held at a constant level and the state as the charging system. The following table listsof charge in the battery will determine how much all of the common problems encountered withcurrent will flow. This is often the fastest way to lead-acid batteries, together with typical causes.recharge a flat battery. If a constant voltage of lessthan 14.4 V is used then it is not possible to causeexcessive gassing and this method is particularly Symptom or fault Likely causesappropriate for sealed batteries. Low state of Charging system fault Boost charging is a popular technique often charge Unwanted drain on batteryapplied in many workshops. It is not recommended Electrolyte dilutedas the best method but, if correctly administered and Incorrect battery for applicationnot repeated too often, it is suitable for most bat- Low capacity Low state of chargeteries. The key to fast or boost charging is that the Corroded terminals Impurities in the electrolytebattery temperature should not exceed 43°C. With Sulphatedsealed batteries it is particularly important not to Old age – active material fallen from thelet the battery gas excessively in order to prevent plates Figure 7.55 Battery charger
  • 174. 158 Advanced automotive fault diagnosisExcessive gassing Overcharging Repairing modern batteries is not possible.and temperatures Positioned too near exhaust component Most of the problems listed will require the bat-Short circuit cell Damaged plates and insulators tery to be replaced. In the case of sulphation it is Buildup of active material in sediment sometimes possible to bring the battery back to trap life with a very long low current charge. A forti-Open circuit cell Broken connecting strap Excessive sulphation eth of the Ah capacity or about a two hundredth Very low electrolyte of the cold start performance for about 50 hoursService life shorter Excessive temperature is an appropriate rate.than expected Battery has too low a capacity Vibration excessive Contaminated electrolyte 7.25.5 Testing batteries Long periods of not being used For testing the state of charge of a non-sealed type Overcharging of battery, it was traditional to use a hydrometer. The Hydrometer is a syringe which draws elec- trolyte from a cell and a float which will float at a particular depth in the electrolyte according to its density. The relative density or specific gravity is then read from the graduated scale on the float. A fully charged cell should show 1.280, when half charged 1.200 and if discharged 1.120. Most vehicles are now fitted with maintenance free batteries and a hydrometer cannot be used to find the state of charge. This can, however, be determined from the voltage of the battery, as given in the following table. An accurate voltmeter is required for this test (Figure 7.57) – note the misleading surface charge shown here. Battery Volts at 20°C State of Charge 12.0 V Discharged (20% or less) 12.3 V Half charged (50%) 12.7 V Charged (100%)Figure 7.56 Battery charger and engine starter Figure 7.57 Battery voltage testing
  • 175. Engine systems 159 Starting test data ● Average cranking current ● Maximum cranking current ● Pre-set voltage ● Pre-set load voltage ● Average cranking voltage ● Minimum cranking voltage. Battery test data ● Diagnosis ● Actual CCA ● Percentage capacity ● Open circuit voltage ● Impedance (often described as internal resistance).Figure 7.58 ‘MicroVAT’, charging system, starter and batterytester (Source: Snap-on). Alternator test data ● Diagnosis ● Failure mode ● Charging at idleTo test a battery more thoroughly, it is now pre- ● Charging volts under loadferred to use a volt, amp tester (VAT). There are ● Average current at idlemany variations on the market; however, this ● Peak currentsection will outline just one type. Snap-on pro- ● Peak to peak ripple at idleduce a compact and very useful tester called the ● Peak to peak ripple under load.MicroVAT (Figure 7.58). This equipment willcarry out a range of diagnostic tests. The device, as with many similar types, willdo not only battery condition tests, but also tests 7.26 Startingon the charging and starting system. This VAT takes advantage of new impedance/current test technology to detect the full range of 7.26.1 Starter circuitbattery failure modes including bad cells, sul- In comparison with most other circuits on thephation, internal short circuits, and other chem- modern vehicle the starter circuit is very simple.ical and physical failures. Testing takes less than The problem to overcome, however, is that of volt5 seconds and will even work on batteries dis- drop in the main supply wires. A spring-loadedcharged down to as low as one volt. key switch usually operates the starter; the same Some of the key features of this tester are: switch also controls the ignition and accessories. The supply from the key switch, via a relay in● Automated system test of battery, alternator many cases, causes the starter solenoid to operate and starter in under a minute. and this in turn, by a set of contacts, controls the● Detailed test data: alternator ripple, internal heavy current. In some cases an extra terminal resistance, starter draw, state of charge, char- on the starter solenoid provides an output when ging amps, and volts. cranking, usually used to bypass a dropping resis-● Tests discharged batteries down to one volt. tor on the ignition or fuel pump circuits. The● Impedance/current (IC) test technology. basic circuit for the starting system is shown in● Wireless printer option. Figure 7.59. The problem of volt drop in the main● Integrated high and low amp probe options. supply circuit is due to the high current requiredMicroVAT uses a fan cooled 50 A load and by the starter particularly under adverse startingintegrated amp probe to test the quantity and conditions such as very low temperatures.quality of alternator output with an alternator A typical cranking current for a light vehicleripple test. Many late model computer-controlled engine is in the order of 150 A but this may peakcharging systems virtually shut down under no in excess of 500 A to provide the initial stalledload conditions. torque. It is generally accepted that a maximum Diagnostic tests that can be carried out with volt drop of only 0.5 V should be allowedthis tester, when an amps probe is also used, are between the battery and starter when operating.as follows. An Ohm’s law calculation indicates that the
  • 176. 160 Advanced automotive fault diagnosis Heavy current wire Starter switch Supply terminal Solenoid switch Light current wire Battery Motor M Buffer spring Pinion Figure 7.60 Inertia type starterFigure 7.59 Starter circuit not applied until the pinion is fully in mesh. They prevent premature ejection as the pinion is heldmaximum allowed circuit resistance is 2.5 m⍀, into mesh by the action of a solenoid. A one-waywhen using a 12 V supply. This is a worst case clutch is incorporated into the pinion to preventsituation and lower resistance values are used in the starter motor being driven by the engine. Anmost applications. The choice of suitable con- example of a pre-engaged starter in common useductors is therefore very important. is shown in Figure 7.61. Figure 7.62 shows the circuit associated with7.26.2 Inertia starters operating this type of pre-engaged starter. The basic operation of the pre-engaged starter is as fol-In all standard motor vehicle applications it is lows. When the key switch is operated a supply isnecessary to connect the starter to the engine ring made to terminal 50 on the solenoid. This causesgear only during the starting phase. If the connec- two windings to be energised, the hold-on windingtion remained permanent, the excessive speed at and the pull-in winding. Note that the pull-in wind-which the starter would be driven by the engine ing is of very low resistance and hence a high cur-would destroy the motor almost immediately. rent flows. This winding is connected in series with The inertia type of starter motor has been the the motor circuit and the current flowing will allowtechnique used for over 85 years, but it is now the motor to rotate slowly to facilitate engagement.becoming redundant. At the same time the magnetism created in the The starter engages with the flywheel ring gear solenoid attracts the plunger and via an operatingby means of a small pinion. The toothed pinion lever pushes the pinion into mesh with the flywheeland a sleeve splined on to the armature shaft are ring gear. When the pinion is fully in mesh thethreaded such that when the starter is operated plunger at the end of its travel causes a heavy-dutyvia a remote relay, the armature will cause the set of copper contacts to close. These contacts nowsleeve to rotate inside the pinion. The pinion supply full battery power to the main circuit of theremains still due to its inertia and, because of the starter motor. When the main contacts are closedscrewed sleeve rotating inside it, the pinion is the pull-in winding is effectively switched off duemoved into mesh with the ring gear. to equal voltage supply on both ends. The hold-on When the engine fires and runs under its own winding holds the plunger in position as long as thepower the pinion is driven faster than the arma- solenoid is supplied from the key switch.ture shaft. This causes the pinion to be screwed When the engine starts and the key is released,back along the sleeve and out of engagement the main supply is removed and the plunger andwith the flywheel. The main spring acts as a pinion return to their rest positions under springbuffer when the pinion first takes up the driving tension. A lost motion spring located on the plun-torque and also acts as a buffer when the engine ger ensures that the main contacts open beforethrows the pinion back out of mesh. the pinion is retracted from mesh. During engagement if the teeth of the pinion hit the teeth of the flywheel (tooth to tooth abutment),7.26.3 Pre-engaged starters the main contacts are allowed to close due to thePre-engaged starters are fitted to the majority of engagement spring being compressed. This allowsvehicles in use today. They provide a positive the motor to rotate under power and the pinionengagement with the ring gear, as full power is will slip into mesh.
  • 177. Engine systems 161Figure 7.61 Supply link wire from solenoid to starter motor Starter switch 7.26.4 Permanent magnet (PM) starters Solenoid Permanent magnet starters began to appear on production vehicles in the late eighties. The two Hold-on advantages of these motors, compared to conven- winding Main tional types, are less weight and smaller size. This Pull-in contact makes the PM starter a popular choice by vehicle Battery winding manufacturers as, due to the lower lines of today’s cars, less space is now available for engine electri- cal systems. The reduction in weight provides a Motor M contribution towards reducing fuel consumption. The principle of operation is similar in most respects to the conventional pre-engaged starter motor, the main difference being the replacementFigure 7.62 Starter circuit (Pre-engaged) of field windings and pole shoes with high qual- ity permanent magnets. The reduction in weight is in the region of 15% and the diameter of the The torque developed by the starter is passed yoke can be reduced by a similar factor.through a one-way clutch to the ring gear. The Permanent magnets provide constant excitationpurpose of this free wheeling device is to prevent and it would be reasonable to expect the speed andthe starter being driven at excessively high speed torque characteristic to be constant. However, dueif the pinion is held in mesh after the engine has to the fall in battery voltage under load and the lowstarted. The clutch consists of a driving and driven resistance of the armature windings, the character-member with several rollers in between the two. istic is comparable to series wound motors.The rollers are spring loaded and either wedge-lock Development by some manufacturers has alsothe two members together by being compressed taken place in the construction of the brushes. Aagainst the springs, or free wheel in the opposite copper and graphite mix is used but the brushesdirection. are made in two parts allowing a higher copper Many variations of pre-engaged starter are in content in the power zone and a higher graphitecommon use but all work on similar lines to the content in the commutation zone. This results inabove description. The wound field type of motor increased service life and a reduction in volt drophas now largely been replaced by the permanent giving improved starter power. Figure 7.63 showsmagnet version. three modern PM starters.
  • 178. 162 Advanced automotive fault diagnosisFigure 7.63 Modern permanent magnet starters 1 Pinion 2 Ring gear 3 Roller type overrunning clutch 4 Engaging lever 5 Planetary gear 6 Permanent magnet 7 Armature 8 Commutator with carbon brushes 9 Solenoid switch with pull-in and hold-on windings 10 Starter switch 11 Battery 1 Drive end shield 2 Pinion 3 Solenoid switch 4 Terminal 5 Commutator end shield 6 Brush plate with carbon brushes 7 Commutator 8 Armature 9 Permanent magnet 10 Field frame 11 Planetary gear (intermediate transmission) 12 Engaging lever 13 Pinion-engaging driveFigure 7.64 PM starter with intermediate transmission (Source: Bosch) For applications with a higher power require- engines up to about 1.6 litres. This form of PMment PM motors with intermediate transmission motor can give a weight saving of up to 40%. Thehave been developed. This allows the armature to principle of operation is again similar to the con-rotate at a higher and more efficient speed whilst ventional pre-engaged starter.still providing the torque, due to the gear reduc- The sun gear is on the armature shaft andtion. Permanent magnet starters with intermedi- the planet carrier drives the pinion. The ring gear orate transmission are available with power outputs annulus remains stationary and also acts as anof about 1.7 kW, suitable for spark ignition engines intermediate bearing. This arrangement of gearsup to about five litres or compression ignition gives a reduction ratio of about 5:1. Figure 7.64
  • 179. Engine systems 163shows a PM starter with intermediate transmission, Solenoid contacttogether with its circuit and operating mechanism. supply terminal Starter switch V4 V77.27 Diagnosing starting V6 Link from solenoidsystem faults V3 terminal to motor7.27.1 Circuit testing procedure M V5The process of checking a 12 V starting system V8operation is as follows. Figure 7.65 Starter circuit volt drop testing Starting systems diagnostic chart Start a circuit with voltmeters connected. The num- bered voltmeters relate to the number of the test in the above list. Hand and eye checks Note that connections to the starter should be (loose wires, loose battery terminals and other obvious made to the link between the solenoid contacts faults) – all connections clean and tight and the motor not to the main supply terminal. Figure 7.66 shows an example of this link. Check battery - must be 70% charged (ideally fully 7.27.2 Starting fault diagnosis charged) table Symptom Possible fault Battery volts (minimum 10 V) Tests including this one, from here onwards are Engine does not Battery connection loose or corroded all carried out while trying rotate when trying Battery discharged or faulty to crank the engine to start Broken loose or disconnected wiring in the starter circuit Defective starter switch or automatic Solenoid lead (same as battery – if not check gearbox inhibitor switch starter key switch) Starter pinion or flywheel ring gear loose Earth strap broken. Loose or corroded Starter noisy Starter pinion or flywheel ring gear loose Voltage supplied to Yes the starter is within No Starter mounting bolts loose 0.5 V of the cranking Starter worn (bearings, etc.) battery voltage? Discharged battery (starter may jump in Insulated line volt drop and out) (maximum 0.25 V)Check engine for seizure Starter turns Discharged battery (slow rotation) or mechanical fault engine slowly Battery terminals loose or corroded Earth strap or starter supply loose or Solenoid contacts volt disconnected drop (almost 0 V) High resistance in supply or earth circuit Replace starter motor Internal starter fault Earth line volt drop (maximum 0.25 V) 7.28 Charging End 7.28.1 IntroductionThe idea of these tests is to see if the circuit is The ‘current’ demands made by modern vehiclessupplying all the available voltage at the battery are considerable. The charging system must beto the starter. If it is, then the starter is at fault, if able to meet these demands under all operatingnot, then the circuit is at fault. Figure 7.65 shows conditions and still fast charge the battery.
  • 180. 164 Advanced automotive fault diagnosis Figure 7.66 Supply link/wire from solenoid terminal to starter motor ● supply whatever charge current the battery demands; ● operate at idle speed; ● constant voltage under all conditions; ● efficient power to weight ratio; ● reliable, quiet, resistance to contamination; ● low maintenance; ● provide indication of correct operation. 7.28.2 Basic principles When the alternator voltage is less than the bat- tery (engine slow or not running for example), the direction of current flow is from the battery to the vehicle loads. The alternator diodes prevent current flowing into the alternator. When the alternator output is greater than the battery volt- age, current will flow from the alternator to the vehicle loads and the battery. It is clear therefore, that the alternator outputFigure 7.67 Bosch compact alternator voltage must be above battery voltage at all times when the engine is running. The actual voltage The main component of the charging system is used is critical and depends on a number ofthe alternator and on most modern vehicles, with factors.the exception of its associated wiring, it is the only The main consideration for charging voltagecomponent in the charging system. Figure 7.67 is the battery terminal voltage when fully charged.shows an alternator in common use. The alternator If the charging system voltage is set to this valuegenerates AC but must produce DC at its output then there can be no risk of overcharging theterminal as only DC can be used to charge the bat- battery. This is known as the constant voltagetery and run electronic circuits. The output of the charging technique. The figure of 14.2 Ϯ 0.2 Valternator must be a constant voltage regardless of is the accepted charging voltage for a 12 Vengine speed and current load. system. Commercial vehicles generally employ The charging system must meet the following two batteries in series at a nominal voltage ofcriteria (when the engine is running): 24 V; therefore the accepted charge voltage● supply the current demands made by some or would be doubled. These voltages are used as all loads; the standard input for all vehicle loads. For the
  • 181. Engine systems 165purpose of clarity the text will just consider a A further three positive diodes are often12 V system. included in a rectifier pack. These are usually The other areas for consideration when deter- smaller than the main diodes and are only used tomining charging voltage are any expected volt supply a small current back to the field windingsdrops in the charging circuit wiring and the oper- in the rotor. The extra diodes are known as theating temperature of the system and battery. The auxiliary, field or excitation diodes.voltage drops must be kept to a minimum but it is When a star wound stator is used the additionimportant to note that the terminal voltage of the of the voltages at the neutral point of the star is inalternator may be slightly above that supplied to theory 0 V. In practice, however, due to slight inac-the battery. Figure 7.68 shows the basic principle curacies in the construction of the stator and rotorof an alternator. a potential develops at this point. By employing two extra diodes, one positive and one negative connected to the star point the energy can be col-7.28.3 Rectification of AC to DC lected. This can increase the power output of anIn order to full wave rectify the output of a three alternator by up to 15%.phase machine six diodes are needed. These are Figure 7.69 shows the full circuit of an alter-connected in the form of a bridge, which consists nator using an eight diode main rectifier and threeof three positive diodes and three negative diodes. field diodes. The voltage regulator, which formsThe output produced by this configuration is the starting point for the next section, is alsoshown compared to the three phase signals. shown in this diagram. The warning light in an alternator circuit, in addition to its function in warning of charging faults, also acts to supply the initial excitation to the field windings. An Stator alternator will not always self-excite as the resid- ual magnetism in the fields is not usually enough to produce a voltage which will overcome the 0.6 N Rotor or 0.7 V needed to forward bias the rectifier diodes. A typical wattage for the warning light Three phase bulb is 2 W. Many manufacturers also connect a S AC output resistor in parallel with the bulb to assist in exci- tation and allow operation if the bulb blows. The charge warning light bulb is extinguished when the alternator produces an output from the field diodes as this causes both sides of the bulb to take on the same voltage (a potential differenceFigure 7.68 Basic alternator principle across the bulb of 0 V). Figure 7.69 Complete internal alternator circuit
  • 182. 166 Advanced automotive fault diagnosis7.28.4 Regulation of outputvoltageTo prevent the vehicle battery from being over-charged the regulated system voltage should bekept below the gassing voltage of the lead-acid bat-tery. A figure of 14.2 Ϯ 0.2 V is used for all 12 Vcharging systems. Accurate voltage control is vitalwith the ever-increasing use of electronic systems.It has also enabled the wider use of sealed batter-ies, as the possibility of overcharging is minimal. Voltage regulation is a difficult task on a vehiclealternator because of the constantly changingengine speed and loads on the alternator. The out-put of an alternator without regulation would riselinearly in proportion with engine speed. Alternator Figure 7.70 Voltage regulatoroutput is also proportional to magnetic fieldstrength and this in turn is proportional to the field Electronic regulators can be made to sensecurrent. It is the task of the regulator to control this either the battery voltage or the machine voltagefield current in response to alternator output volt- (alternator) or a combination of the two. Mostage. The abrupt switching of the field current does systems in use at present tend to be machinenot cause abrupt changes in output voltage due to sensed as this offers some protection against overthe very high inductance of the field (rotor), wind- voltage in the event of the alternator being drivenings. The whole switching process also only takes with the battery disconnected.a few milliseconds. Over voltage protection is required in some Regulators can be mechanical or electronic, the applications to prevent damage to electroniclatter now almost universal on modern cars. The components. When an alternator is connected tomechanical type uses a winding connected across a vehicle battery system voltage, even in thethe output of the alternator. The magnetism pro- event of regulator failure, will not often exceedduced in this winding is proportional to output volt- about 20 V due to the low resistance and swamp-age. A set of normally closed contacts is attached to ing effect of the battery. If an alternator is runan armature, which is held in position by a spring. with the battery disconnected (which is not rec-The supply to the field windings is via these ommended), a heavy duty Zener diode connectedcontacts. When the output voltage rises beyond a across the output will offer some protection as, ifpre-set level, say 14 V, the magnetism in the regula- the system voltage exceeds its breakdown figure,tor winding will overcome spring tension and open it will conduct and cause the system voltage tothe contacts. This switches off the field correct and be kept within reasonable limits. This device iscauses alternator output to fall. As output falls often referred to as a surge protection diode.below a pre-set level the spring will close the regu-lator contacts again and so the process continues. The problem with mechanical regulators is the 7.28.5 Charging circuitswear on the contacts and other moving parts. Thishas been overcome with the use of electronic reg- On many applications the charging circuit is oneulators which, due to more accurate tolerances and of the simplest on the vehicle. The main outputmuch faster switching, are far superior, producing is connected to the battery via suitable size cablea more stable output. Due to the compactness and (or in some cases two cables to increase reliabil-vibration resistance of electronic regulators they ity and flexibility). The warning light is con-are now fitted almost universally on the alternator nected to an ignition supply on one side and toreducing the number of connecting cables required. the alternator terminal at the other. A wire may The key to electronic voltage regulation is the also be connected to the phase terminal if it iszener diode. This diode can be constructed to utilised. Figure 7.71 shows two typical wiringbreakdown and conduct in the reverse direction at circuits. Note the output of the alternator is oftena precise level. This is used as the sensing element connected to the starter main supply simply forin an electronic regulator. Figure 7.70 shows two convenience of wiring. If the wires are kept ascommon electronic voltage regulators. short as possible this will reduce voltage drop in
  • 183. Engine systems 167 the circuit. The volt drop across the main supply wire when the alternator is producing full output current should be less than 0.5 V. Some systems have an extra wire from the alternator to ‘sense’ battery voltage directly. An ignition feed may also be found and this is often used to ensure instant excitement of the field windings. A number of vehicles link a wire from the engine management ECU to the alternator. This is used to send a signal to increase engine idle speed if the battery is low on charge. 7.29 Diagnosing charging system faults 7.29.1 Testing procedure After connecting a voltmeter across the battery and an ammeter in series with the alternator output wire(s), as shown in Figure 7.72, theFigure 7.71 Example charging circuits process of checking the charging system opera- tion is as follows. Charging systems diagnostic chart Start Hand and eye checks (loose wires, loose battery terminals and other obvious faults) – all connections clean and tight Check battery – must be 70% charged Check warning light operation Measure supply voltages to alternator – battery volts Maximum output current (discharge battery by leaving lights on for a few minutes, leave lights on and start engine) – No ammeter should read within Yes Positive circuit volt drop – 10% of rated output 0.5V maximum with voltmeter connected ALT+ to BAT+ Regulated voltage (run the engine until Earth circuit volt drop – the ammeter reading 0.5 V maximum with is 10 A or less) is voltmeter connected ALT– 14.2 ± 0.2 V? to BAT System No Yes Replace or repair alternator System is working correctly End
  • 184. 168 Advanced automotive fault diagnosis Alternator internal fault (diode open circuit, brushes worn or regulator fault, etc.) Open circuit in alternator wiring, either main supply, ignition or sensing wires if fitted Short circuit component causing battery drain even when all switches are off High resistance in the main charging circuit Charge warning Slipping or broken alternator drive belt light stays on when Alternator internal fault (diode openFigure 7.72 Alternator circuit testing engine is running circuit, brushes worn or regulator fault, etc.) Loose or broken wiring/connections If the alternator is found to be defective then a Charge warning Alternator internal fault (brushes worn, light does not open circuit or regulator fault, etc.)quality replacement unit is the normal recom- come on at any Blown warning light bulbmendation. Repairs are possible but only if the time Open circuit in warning light circuitgeneral state of the alternator is good.7.29.2 Charging fault diagnosistableSymptom Possible faultBattery loses Defective batterycharge Slipping alternator drive belt Battery terminals loose or corroded Knowledge check questions To use these questions, you should first try to answer them without help but if necessary, refer back to the content of the chapter. Use notes, lists and sketches to answer them. It is not necessary to write pages and pages of text! 1. Describe how a VAT is used to check battery condition. 2. List in a logical sequence, a series of tests that would determine why an engine, which is cranking over correctly, will not start. 3. Describe how the colour of smoke from a diesel engine can be used as an aid to fault diagnosis. 4. Make a block diagram to show the main components of an engine management system and how it can be considered as a series of inputs and outputs. 5. Describe how a cylinder leakage tester is used to check the condition of an engine.
  • 185. 8Chassis systems8.1 Brakes Caution and regular servicing is required to ensure the following:8.1.1 Introduction ● no air must be allowed in the hydraulic circuits (air compresses and would not transfer theThe main braking system of a car works by force);hydraulics. This means that when the driver presses ● correct adjustment must be maintained betweenthe brake pedal, liquid pressure forces pistons to shoe linings to drums and pads to discs (other-apply brakes on each wheel. A handbrake system, wise the pedal movement would be too large);usually operated by a lever and cables, is used for ● lining materials must be free from contamin-parking. Most hand brakes operate on the rear ation (such as oil, grease or brake fluid).wheels. Two types of light vehicle brakes are used. A separate mechanical system is a good safetyDisc brakes are used on the front wheels of some feature. Most vehicles have the mechanical handcars and on all wheels of sports and performance brake working on the rear wheels but a few havecars. Braking pressure forces brake pads against it working on the front – take care.both sides of a steel disc. Drum brakes are fitted Note the importance of flexible connectionson the rear wheels of some cars and on all wheels to allow for suspension and steering movement.of older vehicles. Braking pressure forces brake These flexible pipes are made of high quality rub-shoes to expand outwards into contact with a ber and are covered in layers of strong mesh todrum. The important part of brake pads and prevent expansion when under pressure.shoes is a friction lining that grips well and with- Extra safety is built into braking systems bystands wear. using a double acting master cylinder (Figure 8.1). This is often described as tandem and can be thought of as two cylinders in one housing. The8.1.2 Principle of hydraulic pressure from the pedal acts on both cylinders butbraking fluid cannot pass from one to the other. Each cylin-A complete system includes a master cylinder der is then connected to a complete circuit. Thisoperating several wheel cylinders. The system is can be by a number of methods:designed to give the power amplification needed ● diagonal split;for braking the particular vehicle. On any vehicle, ● separate front and rear;when braking, a lot of the weight is transferred to ● duplicated front.the front wheels. Most braking effort is thereforedesigned to work on the front brakes. Some carshave special hydraulic valves to limit rear wheel 8.1.3 Disc and drum brakebraking. This reduces the chance of the rear systemswheels locking and skidding. Figure 8.2 shows a typical disc brake, calliper The main merits of hydraulic brakes are as pads and disc. The type shown is known as singlefollows: acting sliding calliper. This is because only one● almost immediate reaction to pedal pressure cylinder is used but pads are still pressed equally (no free play as with mechanical linkages); on both sides of the disc by the sliding action.● automatic even pressure distribution (fluid Disc brakes keep cooler because they are in the pressure effectively remains the same in all air stream and only part of the disc is heated as the parts of the system); brakes are applied. They also throw off water bet-● increase in force (liquid lever). ter than drum brakes. In most cases servicing is
  • 186. 170 Advanced automotive fault diagnosisFigure 8.1 Double acting master cylinder Figure 8.3 Drum brake adjusters – ratchet type Disc brakes provide for good braking and are less prone to brake fade than drum brakes. This is because they are more exposed and can get rid of heat more easily. Brake fade occurs when the brakes become so hot they cannot transfer energy any more, and stop working! This type of prob- lem can happen say after keeping the car brakes on for a long time when travelling down a long steep hill. This is why a lower gear should be used to employ the engine as a brake. It is clearly impor-Figure 8.2 Disc brake calliper and brake pads tant to use good quality pads and linings because inferior materials can fail if overheated.minimal. Disc brakes are self adjusting and replac- Drum brakes operate by shoes being forced oning pads is usually a simple task. In the type shown to the inside of the drum. A common type withjust one bolt has to be removed to hinge the calliper a ratchet for automatic adjustment is shown asupwards. Figure 8.3. Shoes can be moved by double or
  • 187. Chassis systems 171Vacuum chamber with vacuum Diaphragm connection Piston Bell valve Air filter Piston rod Push rod Rear chamber Backing plate Figure 8.4 Vacuum operated brake servo (booster)single acting cylinders. The most common lay- The adjustment procedure stated by the manu-out is to use one double acting cylinder and brake facturer must be followed. As a guide, though,shoes on each rear wheel of the vehicle, and disc most recommend tightening the adjuster untilbrakes on the front wheels. A double acting the wheels lock and then moving it back until thecylinder simply means that as fluid pressure acts wheel is just released. You must ensure that thethrough a centre inlet, pistons are forced out of brakes are not rubbing as this would build upboth ends. heat and wear the friction material very quickly. Drum brakes more affected by wet and heat As an aid to fault diagnosis, the effects ofthan disc brakes because both water and heat are incorrect adjustment are as follows:trapped inside the drum. However, they are eas-ier to fit with a mechanical hand brake linkage. ● reduced braking efficiency; ● unbalanced braking; ● excessive pedal travel.8.1.4 Brake adjustmentsBrakes must be adjusted so that the minimummovement of the pedal starts to apply the brakes. 8.1.5 Servo-assisted brakingThe adjustment in question is the gap between the Servo systems are designed to give little assist-pads and disc and/or the shoes and drum. ance for light braking but increase the assistance Disc brakes are self-adjusting because as as pedal pressure is increased. A common servopressure is released it moves the pads just away system uses low pressure (vacuum) from thefrom the disc. Drum brakes are different because manifold on one side, and the higher atmosphericthe shoes are moved away from the drum to a pressure on the other side of a diaphragm. Theset position by a pull off spring. The set position low pressure is taken via a non-return safety valveis adjustable and this can be done in a number from the engine inlet manifold. This pressure dif-of ways. ference causes a force, which is made to act on● Self-adjusting drum brakes are almost univer- the master cylinder. Figure 8.4 shows a vacuum sal now. On light vehicles a common type uses servo. an offset ratchet which clicks to a wider pos- Hydraulic power brakes use the pressure from ition if the shoes move beyond a certain amount an engine driven pump. This pump will often be when operated. Modern cars frequently have a the same one used to supply the power assisted self-adjusting hand brake. steering. Pressure from the pump is made to act on● Screwdriver adjustment through a hole in the a plunger in line with the normal master cylinder. wheel and drum is also used. This is often a As the driver applies force to the pedal, a servo type of nut on a threaded bar which pushes the valve opens in proportion to the force applied by shoes out as it is screwed along the thread. This the driver. The hydraulic assisting force is there- method can also have an automatic adjuster fore also proportional. This maintains the import- fitted. ant ‘driver feel’.● An adjustment screw on the back plate is now A hydraulic accumulator (a reservoir for fluid quite an old method in which a screw or square under pressure) is incorporated into many sys- head protruding from the back plate moves the tems. This is because the pressure supplied by shoes by a snail cam. the pump varies with engine speed. The pressure
  • 188. 172 Advanced automotive fault diagnosisFigure 8.5 Checking a brake disk with a dial gaugein the accumulator is kept between set pressures Figure 8.6 Rolling road brake tester displayin the region of 70 bar. Warning 4. Check cable operation by using an assistant in If you have to disconnect any components from the car while you observe. the braking system on a vehicle fitted with an 5. Renew the cable if seized. accumulator, you must follow the manufacturer’s 6. Check hand brake operation and all associated recommendations on releasing the pressure first. systems.8.1.6 Brake fluid 8.2.2 Test equipmentAlways use new and approved brake fluid when Note: You should always refer to the manufac-topping up or renewing the system. The manu- turer’s instructions appropriate to the equip-facturer’s recommendations must always be fol- ment you are using.lowed. Brake fluid is hygroscopic which meansthat over a period of time it absorbs water. This Brake fluid testerincreases the risk of the fluid boiling due to the Because brake fluid can absorb a small amountheat from the brakes. Pockets of steam in the sys- of water it must be renewed or tested regularly. Ittem would not allow full braking pressure to be becomes dangerous if the water turns into steamapplied. Many manufacturers recommend that inside the cylinders or pipes, causing the brakesthe fluid should be changed at regular intervals – to become ineffective. The tester measures thein some cases once per year or every 30 000 km. moisture content of the fluid.Make sure the correct grade of fluid is used. Brake roller test (Figure 8.6) This is the type of test carried out as part of the8.2 Diagnostics – brakes annual safety test. The front or rear wheels are driven into a pair of rollers. The rollers drive each8.2.1 Systematic testing wheel of the car and as the brakes are applied the braking force affects the rotation. A measure ofIf the reported fault is the hand brake not holding braking efficiency can then be worked out.proceed as follows.1. Confirm the fault by trying to pull away with the hand brake on. 8.2.3 Dial gauge (Figure 8.5)2. Check the foot brake operation. If correct this A dial gauge, sometimes called a clock gauge or suggests the brake shoes and drums (or pads a dial test indicator (DTI), is used to check the and discs) are likely to be in good order. brake disk for run out. The symptoms of this would3. Consider this: do you need to remove the often be vibration or pulsation when braking. wheels and drums or could it be a cable fault? Manufacturers recommend maximum run out
  • 189. Chassis systems 173figures. In some cases the disk can be re-ground Callipers or Free off or renew if in anybut often it is safer and more cost effective to fit wheel cylinders doubt stickingnew disks. This would also be done in pairs. Brake judder Linings worn Renew Drums out Renew of round8.2.4 Test results Discs have Renew excessiveSome of the information you may have to get run-outfrom other sources such as data books or a work- Squeaking Badly worn Renewshop manual is listed in the following table. linings Dirt in brake Clean out with proper drums cleanerTest carried out Information required Anti-squeal Replace and smear withBrake roller test Required braking efficiency: 50% for first shims missing copper grease line brakes, 25% for second line brakes at rear of pads and 16% for the parking brake. On mod- ern vehicles half of the main system is the second line (dual line brakes). Old 8.2.6 Brakes fault diagnosis vehicles had to use the parking brake as the second line, therefore it had to work Table 2 at 25%Brake fluid Manufacturers specify maximum Symptom Possible causecondition moisture content Brake fade Incorrect linings Badly lined shoes Distorted shoes8.2.5 Brakes fault diagnosis Overloaded vehicle Excessive brakingTable I Spongy pedal Air in system Badly lined shoesSymptom Possible faults Suggested action Shoes distorted or incorrectly set Faulty drumsExcessive Incorrect Adjust it! But check Weak master cylinder mountingpedal travel adjustment condition as well Long pedal Discs running out pushing pads backPoor Pad and/or Renew Distorted damping shimsperformance shoe linings Misplaced dust coverswhen stopping worn Drum brakes need adjustment Seized calliper Renew or free off if Fluid leak or wheel possible and safe Fluid contamination cylinders Worn or swollen seals in master cylinder Contaminated Renew (both sides) Blocked filler cap vent linings Brakes binding Brakes or handbrake maladjusted No clearance at master cylinder push rodCar pulls to Seized calliper Overhaul or renew if Seals swollenone side or wheel piston or cylinder Seized pistonswhen braking cylinder on is worn Shoe springs weak or broken one side Servo faulty Contaminated Renew (both sides) linings on one Hard pedal – Incorrect linings side poor braking Glazed linings Linings wet, greasy or not bedded correctlySpongy pedal Air in the Bleed system and then Servo unit inoperative hydraulic system check for leaks Seized calliper pistons Master cylinder Overhaul or renew Worn dampers causing wheel bounce seals failing Brakes pulling Seized pistonsPedal travels to Fluid reservoir Refill, bleed system Variation in liningsthe floor empty and check for leaks Unsuitable tyres or pressureswhen pressed Failed seals in Overhaul or renew Loose brakes master cylinder Greasy linings Leak from a Replace or repair as Faulty drums, suspension or steering pipe or union required Fall in fluid level Worn disc padsBrakes Shoe return Renew (both sides) External leakoverheating springs broken Leak in servo unit
  • 190. 174 Advanced automotive fault diagnosisDisc brake Worn retaining pins energy conversion is taking place in the brakesqueal – pad Worn discs system. This is the conversion of kinetic energyrattle No pad damping shims or springs to heat energy at the discs and brake drums. TheUneven or Disc corroded or badly scored potential for this conversion process between aexcessive Incorrect friction materialpad wear tyre skidding, even on a dry road, is far less. ABrake judder Excessive disc or drum run-out good driver can pump the brakes on and off to Calliper mounting bolts loose prevent locking but electronic control can achieve Worn suspension or steering components even better results. ABS is becoming more common on lower price vehicles, which should be a contribution to safety.8.2.7 Brake hydraulic faults It is important to remember, however, that for nor- mal use, the system is not intended to allow fasterBrake hose clamps will assist in diagnosing driving and shorter braking distances. It should behydraulic faults and enable a fault to be located viewed as operating in an emergency only. Figurequickly. Proceed as follows. 8.7 shows how ABS can help to maintain steering1. Clamp all hydraulic flexible hoses and check control even under very heavy braking conditions. the pedal.2. Remove the clamps one at a time and check the pedal again (each time). 8.3.2 Requirements of ABS3. The location of air in the system or the faulty A good way of considering the operation of a part of the system will now be apparent. complicated system is to ask: ‘What must the system be able to do?’ In other words, ‘what are the requirements?’ These can be considered for8.3 Anti-lock brakes ABS under the following headings:8.3.1 Introduction Fail safe system In the event of the ABS system failing then conventional brakes must stillThe reason for the development of anti-lock operate to their full potential. In add-brakes (ABS) is very simple. Under braking con- ition a warning must be given to theditions if one or more of the vehicle wheels locks driver. This is normally in the form of a simple warning light(begins to skid) then this has a number of conse-quences: Manoeuvrability Good steering and road holding must must be maintained continue when the ABS system is● braking distance increases; operating. This is arguably the key● steering control is lost; issue as being able to swerve round a hazard whilst still braking hard is● tyre wear is abnormal. often the best course of actionThe obvious consequence is that an accident is Immediate response Even over a short distance the systemfar more likely to occur. The maximum deceler- must be available must react such as to make use of the best grip on the road. The responseation of a vehicle is achieved when maximum Figure 8.7 Advantages of ABS
  • 191. Chassis systems 175 must be appropriate whether the driver applies the brakes gently or slams them on hardOperational Normal driving and manoeuvringinfluences should produce no reaction on the brake pedal.The stability and steering must be retained under all road con- ditions.The system must also adapt to braking hysteresis when the brakes are applied, released and then re- applied. Even if the wheels on one side are on dry tarmac and the other side on ice, the yaw (rotation about the vertical axis of the vehicle) of the vehicle must be kept to a minimum and only increase slowly to allow the driver to compensateControlled wheels In its basic form at least one wheel on each side of the vehicle should be Figure 8.8 ABS block diagram controlled on a separate circuit. It is now general for all four wheels to be controlled on passenger vehiclesSpeed range of The system must operate under all constant or allowed to increase. The maximumoperation speed conditions down to walking pressure is determined by the driver’s pressure on pace. At this very slow speed even when the wheels lock the vehicle will the brake pedal. come to rest very quickly. If the From the wheel speed sensors the ECU calcu- wheels did not lock then in theory late