STARTUNEDInformation for the Independent Mercedes-Benz Service ProfessionalNovember/December 2011      U.S. $6.00   €9.00 ...
TO OUR READERS:Welcome to StarTuned, the magazine for independent servicetechnicians working on Mercedes-Benz vehicles. Yo...
Images courtesy of Mercedes-Benz USA Examples include dedicated "jig and fixture"                                         ...
STRAIGHT TALKvehicle can be locked down to the bench before any                   Romess-Rogg CM-09606 inclinometer, which...
w ESHHInl   ^$BmF     11 I 1 I       f 1 LFLJ             U        Uk                               COLOR-MAX^ METALLIC   ...
STRAIGHT TALKelectronically in an efficient manner throughout the                     and wheel/tire condition are now cri...
two are key pivot mounting points that actually hold                the car until it is in range and then calibrate thethe...
-Technology does not come without                      (Above) If you see a relatively large conventional leadconsequences...
us know that. The larger battery mountedin the trunk is known as the "systems"battery. It supplies power to the accessorya...
POWER PLANTprovides voltage to the accessory power sockets.       control modules are integrated into the cars CANWhen vol...
GENUINE                        MERCEDES-BENZ REMANUFACTURED A/C                                                  COMPRESSO...
•BOHS!Cat Got Your Tongue?   With very few exceptions, the catalytic   converter has been on every gasoline-burning   car ...
makes itself known. To        Vehicle         203.064                                            Control unit ME-SFI2.8kee...
CAT GOT YOUR TONGUE?plugs and compression of any indicated. The               pressure gauge (you want one with a low scal...
New Wholesale Parts Website                                                                   is up and running complete w...
Compliments of R B M OF ATLANTA INC.                                            770-390-0601Dont take a chance with other ...
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Star tuned magazine november december 2011


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Star tuned magazine november december 2011

  1. 1. STARTUNEDInformation for the Independent Mercedes-Benz Service ProfessionalNovember/December 2011 U.S. $6.00 €9.00 Volume I I Number 6 I N THIS ISSUE: 2 STRAIGHT TALK Frame & Suspension Alignment Pose Unique Challenges s POWER PLANT Dual Battery system 1 C A T G O T Y O U R IV 2 Making sure that cats really dead is T H E NET Tech info for you M f c <ay
  2. 2. TO OUR READERS:Welcome to StarTuned, the magazine for independent servicetechnicians working on Mercedes-Benz vehicles. YourMercedes-Benz dealer sponsors StarTuned and provides theinformation coming your way in each issue.Mercedes-Benz wants to present the information you need Straiknow to diagnose and repair Mercedes-Benz vehicles accurately, Frame Realignment andquickly and the first time; text, graphics, on-line and othertechnical sources combine to make this possible. Suspension Alignmer^ PoseFeature articles, derived from approved company sourcefocus on being useful and interesting. Unique Challenges Our digest of technical information can help you solveunanticipated problems quickly and expertly.We want StarTuned to be both helpful and informative, soplease let us know just what kinds of features and otherdiagnostic services youd like to see in it. Well continue tobring you selected service bulletins from Mercedes-Benz andarticles covering the different systems on these vehicles.Send your suggestions, questions or comments to us at:StarTunedOne Mercedes DriveMontvale, New Jersey 07645Phone: 1 800 225 6262, ext. 7112e-mail: andrew.webb@mbusa.comStarTuned is a publication of Mercedes-Benz USA, LLC ("MBUSA"). No part of thismagazine may be reproduced without the express written permission of MBUSA.Editorial and Circulation Offices: 486 Pinecrest Rd., Springfield, PA 19064. Caution:Vehicle servicing performed by untrained persons could result in serious injury tothose persons or others. Information contained in this magazine is intended for useby trained, professional auto repair technicians ONLY. This information is provided toinform these technicians of conditions which may occur in some vehicles or to provideinformation which could assist them in proper servicing of these vehicles. Properlytrained technicians have the equipment, tools, safety instructions, and know-how toperform repairs correctly and safely. If a condition is described, DO NOT assume that atopic covered in these pages automatically applies to your vehicle or that your vehiclehas that condition. StarTuned is a registered trademark of MBUSA. ""In America, we drive on 55- to 75-mph highways. Group Publisher Contributing Editor In certain countries in Europe such as Germany, Christopher M. Ayers, Jr. Tom Nash highway speeds are typically much higher, sometimes with no limit. Mercedes-Benz, a global Editorial Director MBUSA Technical Content Advisor Bob Freudenberger Donald Rotolo automaker, therefore insists on adherence to strict frame and suspension alignment specifications, Contributing Editor MBUSA Project Manager as even small deviations from these specs can Bob Chabot Adam Green compromise vehicle stability and occupant safety, especially when magnified by speed. For those Contributing Editor Art Director & Circulation Mgr. who repair Mercedes-Benz vehicles, there is zero Kerry Jonsson Christopher M. Ayers III tolerance for anything less than using the best resources that the automaker provides. -Effective repair is rooted in accessing and Visit us at our website using the most accurate collision service w w w . M B W h o l e s a l e P a r t s . c o m t o view this issue information, which is available at the Mercedes- and all past issues of StarTuned, along with a wealth of information on Genuine Mercedes-Benz Parts. Benz subscription-based website. Facilities and technicians must also embrace To locate a Mercedes-Benz dealer near you, industry-recognized training that raises technician go t o w w w . m b u s a . c o m . competency to meet the repair challenges posed by
  3. 3. Images courtesy of Mercedes-Benz USA Examples include dedicated "jig and fixture" straightening benches, proprietary diagnostic tools (e.g. factory scan tool, Romess-Rogg inclinometer), based on collision repair procedures described in Mercedes-Benz Workshop Information System (WIS) guidelines at (which provide jigs and mounting instruction, straightening guidance, bodywork repair data, diagrams, and documentation). During manufacture, Mercedes-Benz vehicles are built using jig and fixture systems. Jigs are the key mounting points where a vehicle is attached to an automated assembly line, and also to a collision repair bench system, should a collision repair ever be necessary. Fixtures are measuring points that are used to provide a reference for the proper location of those key mounting points throughout a collision repair. In general, fixtures are not a point that is held and pulled against; rather, the fixture serves as a reference point for key location points to be pulled to before initiating further repairs. -Using dedicated bench systems during collision repair, such as those supplied by Celette Inc. (which is now part of the Azimuth Group) or Car Bench, helps Mercedes-Benz certified collision repair facilities precisely measure, control and monitor thenew materials and inbound technology. In addition, repair. The vehicle must be mounted and securelythe equipment and tools employed to must enable fastened to the bench at points not affected bythe safe and complete repair of any vehicle. the collision using the straightening brackets and vehicle-defined mounting points. This allows -These three requirements enable a vehicle to be dimensional variations in deformed or distortedrestored to the same safety ratings that the vehicle parts to be recognized.had pre-collision. Anything less is a disservice to theconsumer, demonstrates a lack of professionalism, ~Key location mounting points can then beand puts the shop at risk of a charge of negligence. measured and repositioned in accordance with Mercedes-Benz specs and then locked down to prevent movement or damage during further repair.Repair from the inside out Whether a subframe element, suspension mounting "Mercedes-Benz requires that its dealer and point, safety system sensor, engine cradle, strutindependent collision repair facilities be certified tower or some other vehicle element, only accurateby the automaker. In addition to Mercedes-Benz positioning during the repair process can replicateservice/repair information, these certified facilities the same dynamics obtained during manufacture.are required to employ factory-approved equipment,tools, and procedures. It should be noted that "For example, if bench measurement determinedapproved companies develop equipment and tools that these key location mounting points suffered nopredicated on Mercedes-Benz repair information. damage or displacement in the collision, then the November/December 2011 3
  4. 4. STRAIGHT TALKvehicle can be locked down to the bench before any Romess-Rogg CM-09606 inclinometer, which unlikesubsequent repair procedures are performed. If any other similar tools, is essential to measuring andkey location point was damaged or displaced during adjusting ride height for all models.the collision, it can be moved to the proper positionon the bench, using the fixture as a reference point.Once positioned properly, the vehicle can then be Is anyone pulling new vehicles right today?locked down and further repairs initiated. "Fixtures have been around for 70 years or so, and were used mostly with mild steels during most of If a frame element needs to be straightened and their history. But times are changing. The rampingservice information indicates that it can be pulled up of innovations such as high-strength steels,rather than replaced, bench equipment jigs can pull aluminum, plastics, and carbon fiber compositesthe component to its proper position using fixtures as poses numerous challenges to collision repair andreference points. Should a part have to be replaced, to those who make straightening equipment.the fixtures that are located on the bench providereference points for height, length and width that -Risk management has become an entrenchedenable the repair technician to place the new part in necessity. The influx of new vehicle technologyits proper position relative to the rest of the vehicle. has forced insurers and repair facilities to confirm repair via documentation, preferably in an automatic Proprietary diagnostic tools are also essential electronic form. This documentation provides ato proper collision repair. The Mercedes-Benz record of where that vehicle was before, duringStar Diagnosis System (SDS) tool must be used and after collision repair to confirm that properto fully reset, reinitialize, or reprogram sensors realignment was achieved.and modules where needed during the collisionrepair. For instance, recalibration of the steering •"Vehicles are changing dramatically. For example,angle sensor (a key element for electronic stability conventional fixture technology is a mechanicalcontrol) is now a crucial final step in a four-wheel measuring system that locates specific, fixedalignment following a collision. Another tool is the points. Data cannot be documented and inputted Tips for Straightening High Strength Steels Mercedes-Benz vehicles are made with increasing amounts of high-strength steels (HSS) that offer increased strength, improved energy load path control and reduced curb weight. Here are three tips that facilities should be aware of: - Technicians must use the most current service information to know where HSS is located to effect complete, safe repairs. Steel designs in some vehicles have been changed more than once in the course of a model year. • Mild Steel Modern vehicles must be measured thoroughly when H High Strength Steel 0 Advanced High Strength Steel theyve taken a hit. HSS will absorb and transfer energy • i Ultra High Strength Steels Aluminum around the passenger cabin. As a result, distortion and 1 I Plastics O Magnesium damage after an impact does not show up in traditional locations, but rather somewhere else. i Higher-strength steels used today require more pressure at holding points to straighten. If too much pressur one centrally-located point it may tear or distort the metal when pulled, creating more. To prevent this damage, spread the total required pressure over multiple points and pull with simultaneous equalized pressures.4 Mercedes-Benz StarTuned
  5. 5. w ESHHInl ^$BmF 11 I 1 I f 1 LFLJ U Uk COLOR-MAX^ METALLIC fink • f t li Warn is always the goal. And thats where BASF Refinish breaks from the field. Only BASF offers the COLOR-MAX®3 system, which covers every color category in the spectrum and only uses chips sprayed with authentic BASF Refinish paint—not printed with ink. So you are assured a precise match the first time, every time, reducing comebacks and increasing productivity. And remember, BASF Refinish coatings are already approved for use by most major OEMs in North America. BASF For the kind of color matches that also match your customers expectations, call he Chemical Company your local BASF distributor at 1-800-825-3000 or visit registered trademarks ot foose Design and used with perrnissin 0 2009 BASF CoraoraOc
  6. 6. STRAIGHT TALKelectronically in an efficient manner throughout the and wheel/tire condition are now critical to arepair process. To compensate, facilities may use an vehicles directional stability, response, corneringelectronic measurement tool after repair, but these adhesion/balance, tire wear, fuel economy, andrecording procedures are costly in terms of time. safety. Vehicles are also equipped with expensive high-quality tires and wheels, which have high-Realignment equipment manufacturers are replacement costs.retooling in response to inbound materials, associatedprocedures, and time erosion during repair. Is -Mercedes-Benz requires four-wheel alignmentanybody actually pulling new vehicles correctly? on all of its models. To properly align a Mercedes- Benz suspension, technicians must use the "In the near future, vehicle realignment equipment approved equipment, tools, and procedures for anywill see a blending of current and emerging holding alignment procedure.and pulling technologies. Some manufacturerssuggest that dedicated bench equipment will yield —In the mechanical service world, basicto more universal equipment that will: maintenance-level wheel alignments resolve @ Facilitate the holding and straightening of most problems. Minor adjustments to camber, vehicles made of old or new materials. caster, or toe are often enough; otherwise, the 0 Incorporate automatic electronic installation of repair bolts, parts, or kits will measurement and documentation throughout generally correct caster, camber, toe or the the repair process to conserve time. steering angle sensor angles that are within 0.25 ® Accommodate the safe and complete repair of to 0.50 degrees of specs. multiple vehicle platforms, rather than being restricted to just a single platform. —Some techs assume that the included angle (IA), caster, and steering axis inclination (SAI) only need to be measured when components have been bent orSuspension alignment matters too damaged in a collision, but Mercedes-Benz requires~~As vehicle suspensions have become complex, that they be checked during every alignment, even ifproper alignment, ride height, spring position, it is done as maintenance. This is because the latter Suspension Alignment Diagnosis is a Lean Procedure Taking 10 to 15 minutes to properly diagnose a car at the beginning of a suspension alignment allows a more definitive analysis, speeds the actual alignment process, and improves technician efficiency. For example, consider Mercedes- Benz models equipped with front MacPherson strut multilink suspensions. Alignment diagnostics training shows technicians that for this scenario, the set of values for camber, SAI, and IA will fit one of the lines in the table below. That narrows the search for cause(s) of an alignment problem. In some cases, the cause may require further bodyshop repair (e.g. bent frame). Camber SAI 1/ 1 Then Check For: Positive Negative OK Bent lower control arm and frame Positive OK Positive Bent strut, knuckle and ball joint Positive Negative Positive Bent knuckle or ball joint AND bent lower control arm and frame Negative Positive OK Strut tower in at top Negative OK Negative Bent strut, knuckle or ball joint Negative Positive Negative Bent strut, knuckle or ball joint AND strut tower in at top6 Mercedes-Benz StarTuned
  7. 7. two are key pivot mounting points that actually hold the car until it is in range and then calibrate thethe suspension to the vehicle. controller to accept that position as right. Thats the difference being properly equipped makes."During a suspension alignment, ride heightadjustment procedures may require that a specified —Clearly, no customer or facility wants post-weight be placed inside the vehicle cabin to collision repair handling problems, premature tiresimulate a driver being in the vehicle, so that the wear, or stability control problems, or the liabilityalignment simulates the vehicle running at a typical risk should another collision occur. So, shop ownerscurb height. In addition, proper ride height also must see that the approved service information isdetermines spring position, which can also impact easily available to the technicians, and that theyperformance, comfort, and safety. keep up to date on procedures, equipment, and suspension designs. |—Use the Romess-Rogg electronic inclinometerto measure ride height via the position of thetransverse links on front and rear axle drive Never Repair a Mercedes-Benz Wheelshafts. Unlike other tools that are sometimes Wheels are designed to take an up and down poundingused for vehicles with conventional suspensions, all day long, mile after mile. But they are not designed to take an impact - whether from the front or back,the Romess-Rogg tool can handle models that and especially from the side. In addition, wheels areare out of spec as well as those equipped with manufactured from several heat-sensitive alloys - coppereither an Airmatic air suspension or ABC hydraulic for flexibility, magnesium for durability and aluminumsuspension. For example, Airmatic or ABC for lighter weight). When heat is applied, aluminum, forsuspensions specify different ranges for the Romess example, becomes malleable at only 200SF. In addition, unseen microscopic fractures in a damaged wheel mayinclination values, which allow a technician to then compromise its integrity. At high speed or when cornering,use the Mercedes-Benz SDS tool to raise or lower any wheel failure could be catastrophic. 5 ^ CM- 0960( L 1 Bm^^ I • Jr _* 8 H a . | C M-09606 • MM win* m w^^ ^H ., •. ^H^ B H T The ride height for all models — in or out of spec and regardless of suspension type — can be easily measured and adjusted by using the Romess-Rogg CM-09606 inclinometer. Other tools are limited to in-spec vehicles without air or hydraulic suspensions. November/December 2011 7
  8. 8. -Technology does not come without (Above) If you see a relatively large conventional leadconsequences. Mercedes-Benz vehicles are some acid battery (clear case), it is for starting. All jump startingof the most technologically advanced on the planet. should be done here, and you should load test it in theThe features that separate them from ordinary conventional way. This battery requires maintenance, so check the electrolyte level and specific gravity.vehicles are very often the computer systems thatcontrol almost everything from the powertrain the rest of the vehicle. They can be isolated fromand chassis to body and HVAC, and all of them each other when the extra capacity isnt needed,require a stable source of electrical power. As this and combined under heavy electrical loads. Also,situation evolved, changes had to be made to the non-essential electrical consumers can be shut offconventional charging and power supply systems if the total load exceeds the systems keep pace with electrical demands. What most As with any other feedback system, a control unit ispeople do not know about their charging systems necessary to monitor the electrical load and makeis that not much charging is going on at idle. The the necessary changes, such as tapping into oralternator is simply not spinning fast enough to isolating the additional battery.make any appreciable current. The real chargingtakes place on the highway. Even then it is more "There are two variations of the dual-batteryof a trickle charge than a big boost since much of system you will find on Mercedes-Benz vehicles.whats generated is being used up by big consumers You can tell them apart by the size of the batteryas you drive. under the hood. The larger conventional lead-acid battery is on the late 1990s/early 2000s system."Generally, current draw is much less on a sunny The smaller motorcycle-type battery is used on day than on a cold night with rain when the blower the early to late 2000s. The early system uses the motor, headlights, and wipers add to the load. The conventional battery mainly for the starter if the alternator has to supply stable current and voltage other trunk-mounted battery is low. It can also under these varying conditions, so Mercedes-Benz supply current when vehicle demands are high. This developed a dual-battery system that increases is the only battery you should jump start the engine power storage capacity to provide a safety margin - from. It is known as the "starter" battery and theone battery starts the engine and the other supplies red warning tag over the positive battery post lets8 Mercedes-Benz StarTuned
  9. 9. us know that. The larger battery mountedin the trunk is known as the "systems"battery. It supplies power to the accessoryand ignition switch-on functions. Youshould never attempt the jump start thevehicle from this battery. Battel CAUTION—On the later system, a smaller esB ^P-START FORBIDDEN(motorcycle-sized) battery is mountedunderneath the cabin air filter. It is ofthe VRLA (Valve Regulated Lead Acid)type, and uses AGM (Active Glass Mat)construction. It is usually in a black caseand the label identifies the battery typeand specifications. This battery is a sealedunit, but if internal pressure increases to a Ipredetermined point a relief valve opens. instructions before replacing tAGM batteries use absorbent glass mat hold the electrolyte against the internal @ A 230 584 06 17 mmplates. They need to be charged at a verylow level over long periods, or with theAGM settings on your charger. The largersystems battery found on both the olderand newer variations are also of the Dont discard the systems batterys positive post cover as it carries theVRLA type. This is one reason warning not to jump start the vehicle from this post. Also, these VRLA/replacement batteries should be OEM AGM batteries should not be charged as you would a conventional unit. Use low current over a longer period of time, or simply use a chargerfrom your Mercedes-Benz parts supplier. specifically designed to handle AGMs.The rest of the system is designed towork with this type of battery, and anysubstitutions can lead to trouble codes _, mmmand poor performance.—The early system (with the conventional •msa-*rc °02 ++ * I | C O 0235starter battery) has a Vehicle Power V23132-A2001-XKSupply control module. It manages the 12V ; PA makecharging of both batteries with two relays. it One is the cut off relay, and the secondis called the isolation relay. The cut offrelay disconnects the starter battery from 1 ts r m - «-the rest of the charging system when it • o j l & Q J Iis in the relaxed state. When the systemsbattery drops below 10.8 volts, the cut offrelay is energized and the starter batteryvoltage is added to the overall system.It is also energized to allow the chargingsystem to charge the starter battery. The At the base of the windshield under a protective cover is the auxiliary relay. This connects the auxiliary batter to the system either to supplyisolation relay is normally closed and voltage or receive charging current for the auxiliary battery. —• November/December 2011 9
  10. 10. POWER PLANTprovides voltage to the accessory power sockets. control modules are integrated into the cars CANWhen voltage is low, the relay is energized opening network. Remember, substitute batteries were notthe voltage supply circuit to the accessory sockets. made to work with the vehicles battery control unitsThrough CAN messages to the SAM module, other and you may set codes or cause premature failures.accessory consumers such as seat heaters are shut To test these VRLA batteries you will need a testeroff to reduce the electrical load. with an appropriate setting. The Miditronics 717 is one tool that Mercedes-Benz approves for testing -The later system works slightly differently. The these batteries. Knowing how a system works andunder-hood battery is an auxiliary battery, not a properly repairing it properly is what Mercedes-Benzstarter battery. A Battery Control Module (BCM) wants for your customers and your business. |monitors the availablebattery voltage at startup and during heavy MHOPPECKEelectrical loads. It is BaHeriencritical that you donot connect vehicle Mercedes-Benzaccessories directly to 595 901 085this battery as the BCMwill not measure these 12V 95Ah 520ADIN 850AEN Made in Germanyelectrical loads. Alwaysattach accessoriesthrough one of the fusecircuits in the pre-fuse VRLA-BATTERIE NICHT OFFNEN!boxes. The control unitstill controls two relays. VRLA-BATTERY DONT OPEN!The cut off relay stillinterrupts electricalconsumers if batteryvoltage is too low, butnow we have the auxiliarybattery relay that simplyadds an additional powersource to meet the Read the label on the battery and you may see some ratings you are not used to.demands of the vehicle. instance, Ah stands for Ampere Hours and DIN is Deutsches Industrie Norm, the EYou can look at data equivalent ofSAE.You are probably accustomed to looking for the cold cranking amwith your SDS since the reading, This is one difficulty in finding a non-OEM replacement E W T F P RdTTFRV SI5SF ± 5 2 0 BIN ENTER When using an AGM battery tester, you will have to enter the specifications of the battery.You may have to c units you are measuring with to make sure the tester performs the correct test.10 Mercedes-Benz StarTuned
  11. 11. GENUINE MERCEDES-BENZ REMANUFACTURED A/C COMPRESSORS WHY__BiJ^JG_EJslJJJJSl ~ PLACE —We replace more parts than aftermarket b. GINEERED — Designed to meet original OEM draw J F A C T U R E D — Made with same OE components as factory parts. MB L E D — Completely assembled from components and not just repaired. — Tested to new unit standards.ITS ALL IN T H E PROCESSRemanufacturing Process (Genuine Mercedes-Benz)1 . Dismantle core 2. Replace key 3. Test a I 4 . Replace and clean all components 100% other critical components that components. with new OE part. components. do not meet specs.Rebuilt Process (Typical Aftermarket)1 . Identify damaged 2. Replace damaged part or parts. part with non-OE part and clean.
  12. 12. •BOHS!Cat Got Your Tongue? With very few exceptions, the catalytic converter has been on every gasoline-burning car sold in the U.S. since 1975. Over those 36 years, weve sometimes seen them clog and lower engine performance, or lose their efficiency, setting codes and/or preventing a vehicle from passing an emissions test. Heres how to make sure that cats really dead To start the catalytic process, fresh oxygen-rich air is before replacing it. injected into the exhaust stream during engine warm-up fo approximately two minutes. Combined with the rich mixtur of a cold engine, this gets the converter hot enough to -The goals engine designers strive for are basically initiate the oxidation process quickly.maximum fuel mileage, minimum emissions, andperformance that makes the vehicle fun to drive, up, and this situation is called catalyst "punchbut trade-offs must be made to achieve them through." So, the PCM compares the activity ofsimultaneously. When the catalytic converter was the upstream HEGO or A/F sensor to that of thefirst adopted, critics warned that this restriction in one downstream. A good cat will have large oxygenthe exhaust stream would decrease fuel mileage storage capacity, so it will absorb fluctuations inand horsepower, but just the opposite happened. the oxygen content of the exhaust, somewhat as anSince the engines of cat-equipped vehicles could electrical capacitor smoothes voltage variations.have much more efficient calibrations than theprevious "leaner and later" emissions-reducing -The PCM expects to see a big differencestrategies and still meet regulations, performance between the amount of voltage change activity inand driveability actually improved markedly. the upstream sensor and the one downstream. If, instead, it sees that the ratio between the two is-At about the same time, many high-population close to one, the catalyst fails its monitor.states and municipalities started emissionsinspection programs to verify that vehicles were notgross polluters. These tests took a diluted sample Constructionat the tailpipe and measured percentages, parts —The core of a catalytic converter is a ceramicper million, or grams per mile of HC, CO, and NOx honeycomb substrate that maximizes the surfacedirectly. Since 1996, of course, weve had an OBD area that comes into contact with the exhaustII monitor that tests the efficiency of the catalytic gasses. It has a "washcoat" that contains theconverter by means of oxygen or A/F sensors both catalytic material. The irregular surface createdupstream and downstream of the converter, and the by the washcoat further increases the area, whichdiagnostics in the PCM (Powertrain Control Module). gives the converter the maximum chance to burn up the HC and CO, and break down the NOx, in the exhaust. Expensive "noble" metals are suspended inCapacity the washcoat, chiefly platinum, palladium, rhodium,—Whats actually being tested here is the cats and cerium.ability to store and release the oxygen needed tocomplete its reactions. If the engines air/fuel ratio -And here is where a big difference in qualityis rich for too long, the stored oxygen can be used between OEM units and aftermarket replacements12 Mercedes-Benz StarTuned
  13. 13. makes itself known. To Vehicle 203.064 Control unit ME-SFI2.8keep materials costs Self-adaptationdown, non-OEM unitsuse as little of those 008 B28 (Intake manifold pressure sensor)metals as possible, and 181 Self-adaptation enabled YES/J 576 Selfadaptation in idle speed range, right bank of [-1.000. .1.000] 0.368weve seen where they cylindersoften dont last even a 596 Selfadaptation in idle speed range, left bank of [-1.000. .1.000] 0.362 cylindersyear, or cant pass the 577 Self-adaptation in lower partial-load range, right [0.680.. 1.320] 1.000monitor or a emissions bank of cylinders 597 Self-adaptation in lower partial-load range, left [0.680.. 1.320] 1.000test when new. There bank of cylindersare often complications 578 Self-adaptation in upper partial-load range, right [0.680.. 1.320] 1.000 bank of cylinderswith the physical 598 Self-adaptation in upper partial-load range, left [0.680.. 1.320] 1.000installation, too. bank of cylinders Always look at fuel trims frst.You may find a fuel control issue that is adding to the problem. Exhaust leaks can also contribute to the setting of a P0420, P0430. Mercedes-Benzdoes not engage in this type of cost-cutting with its When using the 02 orgenuine replacement catalytic converters, choosing A/F sensors to evaluateinstead to supply units that meet as-new standards the functioning ofof performance, durability, and fit. Such adherence the converter, youre obviously assumingto quality will not only help you avoid comebacks and that the sensors aredissatisfied customers, but also make your job easier good. Shown is an 02 sensor switching rich to lean at about 800mvFeline fatalities at a rate of one Mercedes-Benz catalytic converters are switch per second.engineered to last for the life of the vehicle, so makesure you answer two questions accurately before typically caused by overheating from misfiring oryou replace one. First, has it really failed, or is some continuous running in open loop.other problem reducing its efficiency and causinga code to set? Second, if it is indeed ruined, what "The most common DTCs (Diagnostic Troublecondition caused its destruction? Codes) are P0422 and P0432, which indicate that efficiency is below specs for banks #1 and Cat failures start with the obvious: mechanical #2, respectively, on a "V"-type engine. But thedamage such as a shattered substrate (does it rattle presence of codes doesnt necessarily mean thewhen you hit it with the heel of your hand?), or cat is wrecked, or even significantly degraded, so itperhaps corrosion or metal fatigue in a very old unit, behooves you to do further testing.Next, theres lack of catalytic action, which maybe due to contamination of the metallic elements A false converter DTC is often the result of a slightfrom oil burning, an internal-engine coolant leak, misfire thats below the misfire monitors reportingor silicone from non-sensor-safe RTV. Or, in the threshold. This may add enough extra gasoline tocase of the oxidation section, insufficient fresh air the exhaust stream to exceed the cats oxygenwhether or not an air-injection system is present. storage capacity, thus making the signal from theFor the reduction section, poor catalysis may be downstream sensor jagged enough to set a code.due to an air/fuel ratio thats not being held atstoichiometry (14.7:1 air to fuel by weight) because If youve invested in an SDS, under actual valuesof some electronic engine management problem. you can evaluate the engines "smooth running"Finally, theres melt-down and clogging, which is to isolate any problem cylinders. Check the spark •November/December 2011 13
  14. 14. CAT GOT YOUR TONGUE?plugs and compression of any indicated. The pressure gauge (you want one with a low scale). Or,next thing to look at is fuel adaptations of the remove the upstream 02 or A/F sensor and takemisbehaving bank. If the mixtures are too lean or your reading at its hole in the manifold. Check thetoo rich, the PCM will compensate. If the adaptation specs for the car at hand, but if you see over 1.25limits are reached, you should get fuel trim codes, psi at idle, or more than three psi at 2,000 rpm,but you may see cat efficiency codes first. Try to theres a restriction in the exhaust system.correct any fuel trim issues to get the adaptationnumber as close to 0.0 as possible. Also "smoke" ^Theres yet another direct means: Remove thetest the exhaust to make sure you dont have any converter and shine a light through it. You shouldair leaks. False air can change 02 or A/F sensor be able to see breakage and meltdown. If there arereadings and lead to converter efficiency codes. too many bends in the pipes for a clear view, put your shop vac in its blow mode and use a tapered Also, you can use your SDS to monitor catalytic adapter to force those CFM through the unit. If youconverter operation. You can plot the oxygen sensor hear the sound of the vacuums motor change, flowvoltage scan data in the "Lambda" values. Front is being strangled.02 sensors will switch above and below .5V with anormal mixture. At idle, you will also see the rear One final note: If the vehicle is still under thesensors toggle in a similar fashion. The converter federally-mandated eight year or 80,000 milehas not "lit off," so you will see little to no change emissions warranty and hasnt been abused orfrom front to rear readings. Bring the rpm up to a tampered with, the cat is definitely covered. Whilesteady 2,000 and wait. If the cat is working, you sending your customer back to the dealership willshould see the rear sensor signal start to stabilize mean losing the work, it will make you a hero. |. Of course, here we are relying on properly-functioning sensors. You should also verify that the You can compare the front02 sensor heater has a 12V supply and is properly and rear 02 sensor signal voltages, as we are here.grounded. You can also easily measure the heater This was taken with theelements amp draw. engine in the warm-up phase and at idle. ThePlugged catalytic converter has~~The symptoms of a clogged catalyst are usually not reached operating temperature, so they areanemic power, poor fuel mileage, and, in serious both about the same.cases, backfiring through the intake.—The easiest test for plugging isdone with a vacuum gauge. Notethe reading at idle, then hold rpmat 2,500. The needle will drop when « ../you first open the throttle, thenstabilize. If the reading then startsto fall, excessive backpressure is theprobable cause. But dont stop there. The next stepis to check backpressure directly.If the vehicle has air injection, The two upper traces are from the pre-converter 02 sensors, and the lowerdisconnect the check valve from the traces are post converter. Bank # / is the upper trace and bank # 2 is thedistribution manifold, and plug in a lower. Bank #2s cat is apparently struggling to clean up the exhaust.14 Mercedes-Benz StarTuned
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