1. Introduction to Vehicle
Electronic Systems and Fault
Diagnosis
APTE7504 – Vehicle Electronic Diagnosis
Week 1
Praneel Chand

2. Vehicle Systems
• Motor vehicles remain fundamentally unchanged e.g. engines have
pistons, brakes have discs or drum, suspension has springs etc
• Much of the work done by service technicians is traditional –
checking brakes, oil and filter change etc
• Service work is done to avoid faults or diagnose car owner problems
• Just because modern cars are fitted with electronic devices, it doesn’t
mean they can’t be remedied or assumed that they are the cause of
the problem

3. Vehicle Systems (cont)
• Typical service tasks for modern car
shows ‘traditional’ nature of work
• If a technician does this properly –
safely, methodically & thoroughly,
with proper checks at appropriate
stages,
• He/she possesses some important
attributes needed to service or
diagnose electronically controlled
systems
Service task list [1]

4. Basic Components of Vehicle Electronic
Systems
• A typical vehicle electronic system has
some basic elements
• Electronic control unit (ECU)
• Sensors
• Actuators
• Cables (connecting the elements together)
• There are many types of electronic
systems in a vehicle body
• Door & lighting systems, battery
management, climate control, ABS,
traction control, ESP, smart airbags, etc
• You will learn these systems in depth in
weeks 5-8
Computer
Actuators
Sensors
Processing
Cables
Inputs Outputs
Basic elements of an electronic system

5. Basic Components of Vehicle Electronic
Systems - ECUs
• ECU is central to the operation of the system because it holds the
computing capacity to enable the system to function
• Several ECUs are linked to each other via a communications network
• Knowledge of ECUs and how they operate is important for vehicle
electronic system diagnosis
• You will learn about this in week 2

6. Basic Components of Vehicle Electronic
Systems - Sensors
• Devices that ‘sense’ some physical quantity and produce an electrical
response to represent the quantity
• E.g. wheel speed sensors in ABS
• By looking at samples of types of sensors, general knowledge of
sensors needed for examining and troubleshooting can be obtained
• You will learn about this in week 4

7. Basic Components of Vehicle Electronic
Systems - Actuators
• In vehicles these are usually electro-mechanical devices which use the
electrical outputs from the ECU to perform tasks or actions
• E.g. a solenoid can be used in a cruise control actuator
• Some actuators are purely electrical e.g. transistors and relays in
lighting systems
• By looking at samples of types of actuators, general knowledge of
actuators needed for examining and troubleshooting can be obtained
• You will learn about this in week 4

8. Basic Components of Vehicle Electronic
Systems – Student Activity 1
• In groups, discuss some other elements/components which you think
are needed in vehicle electronic systems
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9. Electronic System Diagnosis and Repair
• Individual components such as ECU, some sensors and actuators are
not designed to be repaired in garages
• Main function of technician is to determine the defective component
in the system and replace that component correctly.
• Actual method for testing depends on the diagnostic system of the
car
• Onboard diagnostics (e.g. OBDII scan tools) or off-board diagnostics
e.g. oscilloscopes or multimeters or a mix of both can be used
• You will learn about scan tools and scopes in Week 3.

10. Electronic System Diagnosis and Repair
• Diagnostic systems point the operator to an area in which the defect
lies. It does not necessarily mean that a particular component in
system is defective
• It is important to be methodical and unwise to start testing things
randomly or try changing parts in the hope to fix the problem by
chance
• In short, the necessary knowledge for diagnostics is in two parts:
• An understanding of the system in which the problem exists
• The ability to apply a logical diagnostic routine

11. Electronic System Diagnosis and Repair
• It is important to be clear about two definitions:
• Symptom(s) – what the user of the system (vehicle) notices
• Fault – the error in the system that causes the symptom(s)
Symptom The effect of a fault noticed by the driver or technician
Fault The cause of the symptom/problem
Root cause This may be the same as the fault, but in some cases it can
be the cause of it
Diagnostics The process of tracing a fault by means of its symptoms,
applying knowledge and analysing test results
Knowledge The understanding of a system that is required to diagnose
faults
Logical procedure A step-by-step method used to ensure nothing is missed
Concern, cause,
correction
A reminder of the process starting from what the driver
reports, to the correction of the problem
Report A standard format for the presentation of results
Diagnostic terminology [4]

12. General Six Step Approach for Diagnostics [1]
(Bonnick)
• An organised and common-sense approach to problem solving is
given below [1]:
1. Collect evidence.
2. Analyse evidence.
3. Locate the fault.
4. Find the cause of the fault and remedy it.
5. Rectify the fault (if different from 4).
6. Test the system to verify that repair is correct.
• Certain steps can be recursive and it may be necessary to refer back
to previous steps as one proceeds to a solution
• Refer to the notes and [1] for more details of each step

13. General Six Step Approach for Diagnostics -
Example
• Consider the case of a vehicle with an engine that fails to start. The six
steps could be:
• Notice that the tasks in each step require an understanding of the system. Also
notice the cause (root cause) and the fault are different in this example
Step Task(s)
1 Is it a flat battery? Has it got fuel, etc.?
2 If it appears to be a flat battery, what checks can be applied, e.g. switch on the headlamps.
3 Assume that it is a flat battery.
4 What caused the battery to become discharged?
5 Assume, in this case, that the side and tail lights had been left on. So, in this case, recharging
the battery would probably cure the fault.
6 Testing the system would, in this case, probably amount to ensuring that the vehicle started
promptly with the recharged battery. However, further checks might be applied to ensure that
there was not some permanent current drain from the battery.

14. Alternative Six Step Approach [2],[4] (Denton
Method)
• An alternative (similar) routine for
diagnostics is illustrated on the
right.
• Steps 3 and 4 form a loop within
the larger loop until the fault is
located. Using a logical method
saves time and effort
1. Verify
 Check the fault
is as described
2. Collect
 Get more
information
3. Evaluate
 Stop and think
logically
4. Test
 Measure and
compare
5. Rectify
 Fix the fault,
replace the
part
6. Check
 Make sure
other systems
still work
Six-stage diagnostic process

15. Six Steps and Three C’s
• The six steps form the three C’s (concern, cause, correction) in the
automotive repairs and diagnostics process. Their relationship is
shown below:
Six-stage process CCC
Verify Concern
Collect
CauseEvaluate
Test
Rectify
Correction
Check
Six-stage process and CCC comparison

16. Alternative Six Step Approach [2],[4] (Denton
Method) - Example
• After connecting a hosepipe to the tap and turning on the tap, no water comes
out of the end. Your knowledge of this system tells you that water should come
out providing the tap is on. The following stages of the diagnostic process are
required:
Step Task(s)
1 Confirm that no water is coming out by looking 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 the hose?
3 Consider what this information tells you, for example, the hose must be blocked or
kinked.
4 Walk the length of the pipe looking for a kink.
5 Straighten out the hose.
6 Check that water now comes out and that no other problems have been created.

17. Alternative Six Step Approach [2],[4] (Denton
Method) – Student Activity 2
• After turning on my computer the screen is blank. Use your
knowledge of computers to complete the stages of the diagnostic
process:
Step Task(s)
1
2
3
4
5
6
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18. Alternative Six Step Approach [2],[4] (Denton
Method) – Student Activity 3
• In the notes, Figure 3 illustrates an eight-step diagnostic procedure
for vehicle systems [3]
• In groups, rearrange/classify these 8 steps into the six step general
diagnostic process.
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19. Electronic System Diagnosis and Repair
• You will learn how to diagnose various vehicle electronic systems later
on in the semester (weeks 9-13)
• You will learn about the scope and of the rectification (repair) process
in the last weeks of the semester

20. References
• [1] A. W. M. Bonnick, Vehicle Electronic Systems and Fault Diagnosis A
Practical Guide for Vehicle Technicians. NY: Routledge, 2013. (ebook in
Unitec library)
• [2] T. Denton, Automobile Electrical and Electronic Systems:
automotive technology: vehicle maintenance and repair. NY:
Routledge, 2012. (available in Unitec library)
• [3] J. D. Halderman, Diagnosis and Troubleshooting of Automotive
Electrical, Electronic, and Computer Systems. NJ: Pearson, 2012.
(available in Unitec library)
• [4] T. Denton, Advanced Automotive Fault Diagnosis: automotive
technology: vehicle maintenance and repair. NY: Routledge, 2012.