All-Wheel Drive and 4-Wheel Drive
Contents
1. General Motors offers a record num ber of vehicles that are driven by all four wheels You ve probably heard them called 4 wheel drive 4x4s all wheel drive 4 wheelers and possibly others But the components in these systems are not all alike their operat Ing principles don t work alike and their Vibe driveline is typical On Demand AWD system All W heel Drive and 4 W heel Drive m operating characteristics aren t alike The following is intended to clear up some of the confusion Definitions All multi wheel drive systems are capa ble of providing engine torque to all four J anuary 2003 Volume 5 No 1 wheels at one time or another This is accomplished by attaching a transfer case to the transmission output to route torque to both front and rear axles Each axle contains a differential to route torque to right and left wheels M ulti wheel drive systems fall into two broad categories determined by the kind of transfer case used In all wheel drive systems the trans fer case has only one speed or range 4 wheel drive systems all contain a transfer case that has two speeds called high range and low range As you will see understanding the var ious features characteristics and operat ing conditions is no longer a simple task Operating Characteristics All Wheel Drive Some all wheel drive systems are called on demand Torque is provided to only one ax2. 02 08 42 005 Snowplow Roof Beacon Lamp Inoperative Install Bypass Harness 2003 Chevrolet Silverado Suburban Tahoe GMC Sierra Yukon XL with Snow Plow Provision RPO VYU and Roof Mounted Lamp Provisions RPO TRW 5G4 02 08 44 018 Diagnostic Information for No Audio Out of Speakers on One or More Channels 2003 Cadillac Escalade Chevrolet Silverado Suburban Tahoe GMC Sierra Yukon XL Hummer H2 with Premium Bose Sound Systems 02 08 46 010A replaces 02 08 46 010 Programming OnStar Module for Canadian French Voice bore ee specified 2003 Passenger Cars LD Trucks Hummer H2 with OnStar 02 08 48 001 Stationary Glass Urethane Adhesives Additional M atenals Recognized 2003 and prior Passenger Cars and Trucks 2003 Hummer H2 02 08 49 004A replaces 02 08 49 004 Instrument Panel Cluster IPC Gauges Read Zero at Times Gauges Inop at Times Male Spe Clas PC 2002 Chevrolet TrailBlazer EXT GMC Envoy XL Oldsmobile Bravada 02 08 63 003 Bumper Fascia Cover Retainers Pulling Out of Fascia Trim Fascia 2002 03 Chevrolet Avalanche 02 08 64 022 Cycling Power Foldin Mirror to Remain in Locked Position After Transport 2003 LD Trucks with Power oe enor Mirror RPO DL3 Hummer Bc Power Folding Exterior Mirror RPO 02 08 110 006 Revised Sunshade Replacement 2002 03 Chevrolet TrailBlazer EXT GMC Envoy XL Oldsmobile Bravada 02 08 127 001 Availability of Rear Parking Assist Sensor Service Harness 20
3. tional information In the flush mode air pressure forces clean transmission fluid through the oil cooler and lines This removes dirty oil and blockages To enhance the cleaning action the oil is agitated with bursts of air The cooler is flushed first in the backflush direction then the normal flow direction Waste oil is collected in a built in waste tank After flushing use the digital flow rate indica tor in the J 45096 to perform a flow test The User s Manual includes minimum flow rate charts TIP Minimum flow rates vary depending on whether the oil cooler is made of aluminum or steel And the flow rates also vary with temper ature Be sure you determine both these facts before performing the flow test The flow test indicates whether the oil cooler and cooler lines still have restrictions which must be addressed before the repair is com pleted If required the TransFlow will provide an encrypted 7 digit warranty code following the flow test The entire flush and flow test procedure takes only 5 8 minutes The waste tank can be emptied either using a suction hose in the port provided or by draining from the built in drain fitting at the bottom of the tank In either case the waste oil can be disposed of the same as any other drained transmission fluid Procedures in SI will be changed to accom modate the new J 45096 flush and flow tester Thanks to Dan Popoff Russ Dobson and Dave Roland
4. leak you re looking for hap pens to be between the filler neck and the filler cap removing and replacing the cap for testing could cause the leak to disappear TIP It s recommended that the fuel tank not be full before performing a smoke test size how often the fas tener has been used and the fit of the wrench on the bolt head Consistent clamp load is always important but has taken on a new level of concem in modem lightweight engine compo nents Ovetightening can lead to distorted parts such as cylinder bores and undertightening can lead to leaks and parts coming loose Torque to Angle It s become fairly com mon to temporarily assemble parts to the proper clamp load before machining them For instance cylinder bores are machined with bore plates bolted and torqued into place on the engine block Connecting rod and crankshaft bearing bores are machined with the caps torqued into place When these parts are assembled in the plant or reassembled in the ser vice department after repair it s neces Sary to apply the same consistent torque to the fasteners to ensure that the parts assume their proper as machined shapes When a bolt is tightened it stretches a 7 This is because in some vehicles the fuel filler neck enters the tank from the Side If the fuel is above this level smoke from the service port has to pass through liquid fuel to reach the filler neck and cap Most or all of the
5. smoke will dissolve in the fuel and may not reach the filler area So to be sure you ve tested everything in the system for leaks it may be neces sary to smoke the system from both the service port and from the filler neck Numerous filler neck adapters are sup plied for this purpose Importance of Testing with the Flowmeter Many vehicles do not have an EVAP service bay test to determine if an effec tive EVAP leak repair has been done So the flowmeter in the EEST is the only practical method to be sure you ve actu ally located and repaired a small leak TIP You will learn in the accompanying article that the EONV small leak self test will not report a pass fail until it has run three successive small leak diagnostics This takes three days of operation at the very least Again use the flowmeter to determine if you ve made a proper repair With most systems using the flow meter is a good way to prevent come backs But with EONYV it s impossible to know you ve made an effective repair by any other means Thanks to J ack Woodward little This is called elas tic deformation When the bolt stretches its clamp load is very pre dictable When a bolt tums one revolution it moves a distance equal to the distance between two adjacent threads For instance a bolt with 18 threads per inch moves 1 18 Inch per revolution Engineers can deter mine the amount of stretch a bolt needs to apply th
6. the presence or absence of natural pressure changes to detect leaks If there is even a tiny leak the expected pressure changes do not occur In the sealed system a finite amount of pressure or vacuum will be seen With a 0 020 inch 51 mm leak present little or no pressure or vacuum is observed Experiment At room temperature tighten the cap Railway tanker collapsed due to trapped vacuum on an empty plastic soda pop bottle and put it in the refrigerator After a few min utes look at the bottle As the air temperature in the bottle drops so does pressure indicated by the Plain bottle left collapsed after refrigerating right partial collapse of the bottle This is an oversimplified representation of what happens to a fuel tank after shut down when the fuel and tank cool down With even a tiny pinhole in the pop bottle or cap this will not occur because the leak permits the pressure within the bottle to equalize with the air pressure around the bottle What s Different About the EVAP Hardware on EONV Systems Actually none of the hard ware has changed All of the Same plumbing solenoids valves and fuel tank pressure vacuum sensor are the same The software in the PCM has changed to make the test run and the canister vent solenoid is wired to battery voltage instead of Ignition 1 Previous leak detection methods were performed with the engine running EONV monitors EVAP
7. 01 03 Chevrolet Venture Oldsmobile Silhouette Pontiac Montana tighten bolts 1 2 3 6 7 8 9 10 11 14 16 17 an additional 60 tighten bolts 15 and 18 an additional 45 tighten bolts 4 5 12 13 an additional 30 Measuring the tightening in degrees is the purpose of the J 45059 Angle Meter Using the J 45059 Angle M eter These are the highlights Refer to the instructions that come with the meter for full details The J 45059 Angle Meter is designed for use with a standard 1 2 inch drive extension and a ratchet or torque wrench TIP The bolt must already be tightened to the specified Initial torque before final angle tightening Begin by turning the meter on the last set value will display Use the up down arrows to set the display to the desired angle value The range is 0 199 in 1 increments Attach the meter to the 1 2 inch extension as close as practical to the socket 8 using the spring loaded clamp Install the socket to the bolt Without tuming the bolt apply pressure in the direction of tightening to remove all free play from the wrench Then press the On Zero button and hold until the meter sounds a Short beep and flashes Tighten the bolt When the pre set angle is reached the meter sounds along beep and flashes After use the meter will shut itself off within a minute to con serve battery power Thanks to Tracy Flood and Ron M inoletti
8. P2 NP3 NP3 NP4 NP4 NP8 NP8 NR3 None NR4 Incl With JL4 RPO None None None unusual or typical is to operate a similar vehicle under similar conditions It s necessary to drive the vehicle under conditions that duplicate the cus tomer s concem Be sure to try all ranges in both 2 and 4 wheel drive Try the Auto range if equipped Drive in Straight lines and also in circles TIP In part time 4WD systems it s important that all tires are the same cir cumference to avoid driveline binding and the resulting crow hopping Tires Should be not only the same size but also the same brand and type This is because circumferences can vary a lit tle among brands and types It may not be much but it can be enough to cause problems Proper and even tire Inflation is also extremely important and frequently overlooked And exces Sive wear of one tire can cause differ ent circumferences Thanks to BJ Lackey 4WD AWD vehicles all along But today s vehi cles are made to operate and ride more quietly so these normal noises and sensations are more noticeable One way to determine if a noise or condition is Current Transfer Case Applications TRUCK TRANSFER CASE VEHICLE a STYLE Trackere oo 2 speed manual shift Trailblazer 52 WE 226 2 speed active no pre load NVG 263 2 speed electric shift new electrical HD 2500 3500 Silverado Sierra 2003 EAU HD SHD arc
9. SI terminology EXAMPLE Engine Mechanical Within the sub category your search results are arranged by 5 digit labor codes followed by the labor operation titles Click on your choice to see the operation number along with the labor time associat ed with that number expressed in hours and tenths TIP Add times are also displayed when appropriate Thanks to Terrie Nicholson and Lisa Scott Smoke M achine Revisited In the November 2002 issue we cov ered the operating principles and diag nostic tips for the EVAP system on the Pontiac Vibe and Chevrolet Prizm This month we re covering the EONV system used on some 2003 trucks So it s appropriate to revisit the J 41413 200 Evaporative Emission System Tester the EEST or smoke machine which we first covered in the November 2001 issue Here are some additional pointers you may find useful J 45059 Angle Meter The new essential J 45059 Angle Meter has just been shipped to dealers It is used to ensure proper fastener tight ness when using the torque to angle pro cedure The new meter is unlike earlier torque angle meters in several ways First it does not require an anchor arm so It s very convenient to use even in confined places Second it does not measure the initial torque just the final angle So you ll use your normal torque wrench plus the angle meter A Brief Look at the Science of Tightening Fasteners Friction is
10. TransFlow connectors Labor Time Guide Redesigned Effective February 1 2003 the GM Labor Time Guide will be redesigned It will now have the same overall appearance and function as other GM service documents such as SI and owner s manuals The new Labor Time Guide will be sent to you on two CDs one containing the application and the other containing the data In the future you will receive updates every second month months with even numbers such as April J une etc Usage Tips To use the new Labor Time Guide you must first build the vehicle in question This is done by using pulldown menus to Specify model year make and model Fie Jej hl a ie Mel d ee iain mapir Cahejores x Wee te Blin biati i reese for nemh oelecion EXAMPLE 2003 Buick LeSabre Click Next then click Labor Time Guide You can now search for specific labor operations three ways By name using common industry nomenclature By number if you know it By menu Spaces are provided for you to type in the name or number The menu lists the operation categories by letter and by name If you are unsure of the exact terminology or number this is probably the best way to conduct your search Simply click your choice These names follow SI terminology EXAMPLE J Engine In most cases the next screen presents Sub categories within the broad category Again click on your choice These names also follow
11. ation and elevated operating temperatures which can lead to premature transmission failure Many repeat repair cases can be prevented by following published proce dures for transmission oil cooler flushing and flow checking J 45096 TransFlow is a transmission oil cool ing system flusher and flow tester and will be released in December A major advantage of this new tool is that it uses conventional Dexron III automatic trans mission fluid as the cleaning agent Unlike earli er oil cooler flushing tools it doesn t use deter gents other chemical cleaning agents or hot water so there is no hazardous waste to dis pose of The J 45096 TransFlow is installed in a wheeled cabinet similar to the ACR 2000 air conditioning service station It is equipped with 32 quart oil supply vessel 34 quart waste oil vessel air pressure supply fitting digital flow rate indicator 10 foot 12V DC power cable 10 foot black supply oil hose with quick con nect fitting 10 foot clear waste oil hose with quick con nect fitting The TransFlow equipment is connected to the vehicle s transmission oil cooler lines using the current cooler line adapters Two adapters are included with the TransFlow Five other adapters have been released in the past And three of the common ones are available in the J 45096 KIT All of these are itemized and illustrat ed in the User s Manual Contact Kent M oore at 1 800 345 2233 for addi
12. atmosphere According to OBD II rules the vehicle must perform self tests periodically to detect and indi cate the presence of leaks The present Standard requires being able to detect leaks as small as 0 020 inch 0 51 mm The new Engine Off Natural Vacuum EONV diagnostic system is used on the following 2003 trucks with V6 and V8 engines federal emission vehicles with GVW of 8600 pounds 3900 kg or less California emission vehicles with GVW of 14 000 pounds 6350 kg or less For the applicable vehicles the EONV diagnostic replaces only the previous Small leak detection method All of the other EVAP system component tests are still used during engine operation These include large leak restricted vent exces Sive vacuum and others Then after shutdown the EONV test runs provided all of the engine on tests passed Operating Principles EONV uses the natural pressure changes in the fuel tank to detect leaks Pressure in a sealed container follows temperature changes That is pressure rises when temperature rises Pressure drops when temperature drops While a vehicle is driven the fuel in the tank is warmed even on retumless fuel systems by warm air from the engine radiator and exhaust system Pressure increases in the fuel tank This is true even in cold ambient tempera tures After shutdown pressure nses for awhile then eventually drops when the fuel in the tank cools The EONV system uses
13. e proper clamp load This is related directly to the amount the bolt is turned in degrees By specifying how far the bolt has to be tumed measured in degrees after a preliminary torque is reached the oe can precisely control clamp Oad A typical cylinder head installation may call for tightening the bolts in stages For instance on the L18 head bolts first torque to 30 Nm On the second pass verify 30 Nm and torque 120 in sequence On the third pass depending on bolt length continued on page 8 Bulletins December 2002 This review of service bulletins released through mid December lists the bulletin num ber superseded bulletin number if applica ble subject and models 99 00 89 015B replaces 99 00 89 015A Light Service Support Vehicle LSSV 1999 2003 Chevrolet Silverado Suburban Tahoe 4WD Models with Military Upfit 02 01 39 007 Automatic Dual Zone HVAC Battery Draw 2003 LD Trucks and Hummer H2 02 02 32 012 Rattle Knock Noise When Turning While Driving Over Rough Roads No Fix at This Time Fix Under Development 1999 2002 Chevrolet Cavalier Pontiac Sunfire 01 03 10 012A replaces 01 03 10 012 Guidelines for Using E2020 Wheel Alignments E2000 Toe Adjust and E0200 E0201 E0203 E0204 Wheel Balance 1989 2003 Passenger Cars and LD Trucks 2003 Hummer H2 01 04 18 001A replaces 01 04 18 001 Driveline Characteristics for All Wheel and Four Wheel Drive Systems 2003 and Prior LD Truck Model
14. est The rationality test determines if the refueling detection was caused by an intermittent signal or an actual refueling of the vehicle During the test the PCM checks to see if the cur rent fuel level is greater than the initial fuel level for a calibrated amount of time If the calibrated amount of time passes and the PCM is not able to determine whether the fuel level is greater the refu eling event is declared irrational and a DTC Is set for the sensor that falsely detected the refueling event Other TIP Because the PCM remains on dur ing the EONV test serial data may be observed using the Tech 2 You can watch the vent valve commands and the values from the FTP sensor for instance After the PCM completes the EONV test it powers down and serial data stops TIP If a customer is going to take their vehicle to an I M inspection station after service involving clearing DTCs explain that they should wait four days The EONV test usually runs only once per day due to the cold soak requirement And the I M status bit flag will set ready complete only after at least three successful completions Thanks to J ack Woodward Chad Lehner and J eff Kemph Transmission Oil Cooler Flush and Flow Testing Kit GM studies indicate that restricted transmis sion oil flow is detrimental to the life of any automatic transmission Plugged oil coolers and oil cooler line restrictions cause insufficient transmission lubric
15. hitecture S 10 Sonoma Jimmy Blazer NVG 233 2 speed electric shift NVG HD 2500 3500 Silverado Sierra 261HD SHD 2 speed manual shift Silverado Sierra NVG 261 2 speed manual shift 1 speed full time AWD viscous G H Van Express Savana BW 4473 coupling 1 speed full time AWD viscous Denali Sierra Silverado SS NVG 149 coupling 1 speed on demand AWD active t Safari Astro NVG 136 case with pre load 1 speed on demand AWD active t Bravada NVG 126 case without pre load 2 speed active t case selectable Silverado Sierra Tahoe Yukon Suburban Yukon XL Avalanche NVG 246 2 speed active t case selectable 2003 EAU new electrical architecture 1 speed full time AWD open Denali Escalade BW 4481 differntial with traction control 2 speed full time AWD open differential with traction control high Hummer H2 BW 4484 and low range lock 2 speed full time AWD open differential with traction control low Tahoe Yukon Suburban Yukon XL BW 4482 range lock NOTE ACTIVE 2 SPEED HAS AUTO 4WD 2HI 4HI 4L0 ACTIVE 1 SPEED HAS AUTO 4WD ONLY CAR TRANSFER CASE VEHICLE A B Aztek Rendezvous STEYR the a rear drive module AWD on demand gerotor pump at the a rear drive module AWD on demand viscous coupling U V Montana Venture Silhoutte STEYR Vibe at the rear axle 4T65E Transaxle Conditions Owners of 2003 vehicles equipped with the 4T65E automatic transaxle RPO MN3 MN7 M15 and M76 may experi ence har
16. le until its wheels slip Then torque is also supplied to the other axle The decision of when to distribute torque to the second axle and how much may be made electronically or mechanically Another kind of all wheel drive system is called full time In these torque is supplied to both axles all the time in vari ous amounts When wheels on one end continued on page 2 All W heel Drive and 4 W heel Drive l Know How Broadcasts for February 2 4T65E Transaxle Conditions 005 3 Engine Off Natural Vacuum Diagnostic 4 Transmission Oil Cooler Flush and Flow Testing Kit 6 Labor Time Guide Redesigned 6 Smoke Machine Revisited ccs eae 7 45059 Angle Meter ccc eee eae 7 BUIICHINGY E E N TE ETE 8 continued from page 1 of the vehicle begin to slip torque is routed to the opposite end where trac tion is still present Although operation of all wheel drive vehicles is mostly transparent they can make more noise and have more unusual characteristics than 2 wheel drive sys tems There are more parts rotating and more gears meshing When an on demand system engages the second axle the occupants may hear and feel the components working The driver may also be aware of sensations and noises when making tums even on high traction surfaces where the second axle is not called on to operate 4 Wheel Drive Part Time In part time 4 wheel drive
17. ngine 02 06 04 053 Revised DTC P0403 Exhaust Gas Recirculation EGR Solenoid Control Circuit 2000 Chevrolet Venture Oldsmobile Silhouette Pontiac Montana with 3 4L Engine VIN E RPO LA1 02 06 04 055 Vehicle is Difficult to Fill with Fuel Install Fuel Filler Baffle 2003 Chevrolet Express GMC Savana Except with Left Side Door and Cutaway Cube and Cab Chassis 02 06 05 005 Exhaust M uffler Heat _ Shield Rattle Popping Noise Under Vehicle Install Heat Shield Retaining Straps on Muffler 2002 Cadillac Escalade GMC Denali with 5 3L or 6 0L Gas Engine VINs T N RPOs LM7 LQ9 02 07 30 032A replaces 02 07 30 032 Allison Transmission Control Module FastLeam Procedure Update Required After Transmission Repairs 2002 03 Chevrolet Silverado GMC Sierra with Allison 1000 Series Automatic Transmission 02 07 30 040 Difficult Shifting from Park to Drive Range Replace Shift Indicator ree loor Console 2001 02 Pontiac e 02 07 30 042 Allison Transmission Service Repairs specified 2003 Chevrolet Kodiak and GMC TopKick models with Allison 1000 2400 Series Transmission 02 07 30 043 Allison Transmission Service Repairs 2001 03 Chevrolet Silverado and GMC Sierra HD 2500 and 3500 with Allison 1000 Series Auto Transmission RPO M 74 02 7 30 048 Pressure Control Solenoid Replacement for 4T65 E 4T40 E and 4145 E Transaxle Transmission specified 2000 03 vehicles with RPO Codes MN4 MN5 M13 M15 MN3 MN7 OR M76
18. ob Savo GM Parts and Service Operations lt bob savo GM com Publisher amp Editor Mark Stesney GM Parts and Service Operations lt M ark Stesney GM com Technical Editor J im Horner lt lt im Horner SandyCorp com 1 248 816 3641 Production M anager Marie Meredith Desktop Publishing Greg Szpaichler M ediaW urks lt pake mediawurks com FAX number 1 248 649 5465 Write to lt TechLink PO Box 500 Troy MI 48007 0500 GM TechLink on the Web C http Service gm com General Motors service tips are intended for use by professional tech nicians not a do it yourselfer They are written to inform those techni cians of conditions that may occur on some vehicles or to provide informa tion that could assist in the proper Service of a vehicle Properly trained technicians have the equipment tools Safety instructions and know how to do a job properly and safely If a con dition is described do not assume that the bulletin applies to your vehi cle or that your vehicle will have that condition See a General Motors deal er servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information Inclusion in this publication is not nec essarily an endorsement of the indi vidual or the company Copyright 2003 General Motors Corporation All rights reserved continued from page 2 RPO None None NP1 NP1 NP2 N
19. over The pressure threshold is a function of predicted ambient temperature and fuel level If a vacuum occurs the diagnostic Switches directly to vacuum testing without bleed down If the pressure threshold is not reached the PCM records the peak pressure that is reached and adjusts the vacuum threshold for the vacuum test Then the PCM opens the canister vent valve and waits for system pressure to bleed down The pressure must decay a calibrated amount from the peak pressure for the PCM to consider it a peak and switch to the vacuum test The adjusted vacuum threshold equals the difference between the pressure peak and the pressure threshold Vacuum Test During vacuum test ing the PCM closes the canister vent valve and monitors the tank vacuum to determine if the vacuum threshold is reached If the vacuum threshold is reached Indicating that the system can hold a vacuum the diagnostic passes and the test is complete If the vacuum threshold is not reached the PCM must compare this with previously stored tests before determining whether to call it a fail This is explained below TIP These individual test results can not be displayed on the Tech 2 After at least three successful completions the pass flag will display Diagnostic Result The PCM quantifies the diagnostic result incorporating the results of the pressure and vacuum tests The current result is compared with the previousl
20. quately warmed up certain DTCs not present Refer to SI for specifics There are three tests that make up the EONV diagnostic volatility pressure and vacuum Volatility Test The EONV diagnostic IS very sensitive to large amounts of fuel vaporization due to high volatility fuel The volatility test makes sure the vapor ization rates will not negatively affect the test results The EONV volatility test runs immedi ately after key down if all the enable cn teria have been met The PCM monitors pressure for a calibrated amount of time with the canister vent open and uses pre programmed values to predict fuel volatil ity The logic behind this test is that if pressure builds in the system with the canister vent open it will certainly be able to mask a 0 020 inch 51 mm leak with the vent closed If the test determines that the volatility of the fuel is high the PCM aborts the diagnostic If the fuel is moderately volatile the diagnostic runs with com pensation for volatility For low fuel volatility the diagnostic runs without cor rections Pressure Test The pressure test begins by closing the canister vent sole noid and observing the pressure increase inside the fuel tank At this point the fuel is still warm enough for some amount of vaporization to occur If the pressure increase reaches the calibrated pressure threshold the diagnostic passes meaning the system is leak free and the test is
21. s with AWD or 4WD 02 04 21 006A replaces 02 04 21 006 Inoperative 4WD AWD Lamps or System 2002 03 LD Trucks with Electronic Shift or ane Transfer Case RPO NP1 NP4 or 02 05 22 004B replaces 02 05 22 004 Trailer Brakes Applied When Headlights Park Lamps Are On Brake Controller Illumination M odify Brake Controller Wiring Harness specified 2002 03 LD Trucks and Hummer H2 02 05 27 001A replaces 02 05 27 001 Antilock Brake System ABS Indicator _ Illuminates When Power Takeoff PTO is Engaged Replace Electronic Brake Control Module EBCM specified 2001 02 Chevrolet and GMC Trucks with Air Antilock Brakes RPO J E5 and Allison Auto Transmission 02 06 01 022A replaces 02 06 01 022 Information on Engine Ticking specified LD Trucks 2002 03 with 6 6L Duramax Diesel Engine VIN 1 RPO LB7 02 06 03 012 Proper Diagnostic Procedures for No Start No Crank Battery Generator Gauges SES SIR Brake ao Theft ABS Hot DIC Messages Lamp Light Diagnostic Testing 1997 2003 Passenger Cars LD Trucks Hummer H2 02 06 04 026A replaces 02 06 04 026 Engine Backfire and Related Driveability Issues 1999 2002 Chevrolet and GMC B7 School Bus and C6 7 Conventional Cab MD Models with 7 4L or 8 1L Engine VINs B E RPOs L21 L18 and IMPCO Quantum Technologies LPG Fuel System 02 06 04 052 Engine Stalls No Start Hard Start Repair Fuel Pump Feed Circuit 1990 2002 Chevrolet and GMC H6 7 C Series MD with Gas E
22. se in Neutral may result in noise and shifting into or out of Neutral can result in Some normal gear clash 4 Wheel Drive Full Time The automatic 4 wheel drive system provides torque to all four wheels all the time similar to the all wheel drive sys tem But like other 4 wheel drive sys tems it also has a low range The driver can select depending on the model 4 HI 4HI Lock 4 LO Lock and neutral Typical full time 4WD transfer case 4 Wheel Drive Active This system provides the driver with five choices 2 HI Auto 4WD 4 HI 4 LO and neutral These vehicle can be driven continu ously in Auto although there is a fuel economy and noise penalty When driven in 4 HI or 4 LO these vehicles can experience crow hopping as well However when driven in Auto the operation of the clutch pack compen Sates for different driveshaft speeds All Systems Some noises in these vehicles aren t new they ve been present in Know How Broadcasts for February Emerging PEDRA 12 9 00 AM 12 30 PM Issues 200 3 30 PM EasternTime Technolog Close Up Thanks to Tracy Timmerman February 27 2007 9 00 AM 12 30 PM 3 30 PM EasternTime GM TechLinkis a monthly magazine for all GM retail technicians and service consultants providing timely information to help increase knowl edge about GM products and improve the performance of the service department M anager Product Readiness R M B
23. sh shift TCC shudder during decel TCC applied in 2nd gear and DTC P0742 This may be caused by an inter nal failure of the PWM solenoid Determine the date code located on the electrical connector Replace the solenoid if the date is between 2217 and 2240 The suspect solenoid leaks between the O rings shown Transmissions with build dates before date code 254 stamped on upper right Side of transmission tag are considered to contain the suspect PWM solenoids To determine if the solenoid is the cause of the conditions test drive the vehicle with the Tech 2 connected and monitor Transmission Release Pressure The status should be YES until TCC applies then the display should read NO Suspect the PWM solenoid if the sta tus remains NO during accel the upshifts are harsh and the vehicle shud ders during downshifts during decel Another approach is to connect a Tech 2 shift to Drive range and manually apply third gear with the Tech 2 If the engine stumbles and or stalls suspect the PWM solenoid Replace the PWM solenoid item 334 in the 4T65E Technician s Guide The current part number is 24214974 and the Labor Operation Number is K6557 IMPORTANT Do not replace the valve body if all valves appear to operate freely Thanks to Darryl Butler Engine Off Natural Vacuum Diagnostic The EVAP system on a vehicle is intended to prevent evaporated fuel vapor in the fuel system from leaking out into the
24. system pressure or vacuum with the key off So it may take up to 40 minutes for the PCM to power down TIP This is important to remember when performing a parasitic draw test on vehicles equipped with EONV To avoid battery rundown the diagnos tic limits the number of tests run over a Specific period of time When an EONV test passes the calibrated time between tests is lengthened Step by Step Operation Although the EONV test runs after engine shutdown the process actually begins even before the engine is started That s because the EONV test can be enabled only after all other engine run Fuel Tank te Canister vent valve EVAP system components unchanged ning EVAP tests have run which requires a long cold soak shutdown For all practi cal purposes this limits the EONV to occur not more than once per day A long cold soak meets these requirements start up intake air temperature IAT is between 39 86 F 4 30 C start up engine coolant temperature ECT is less than 86 F 30 C start up IAT and ECT are within 15 F 8 C of each other After startup the following must also be satisfied before EONV is enabled ambient temperature must be between 40 and 96 F 4 and 35 C For more information on this see Sub Functions below fuel level between 15 and 85 full engine run time distance traveled and engine coolant temperature must indicate that the system is ade
25. systems torque is normally sent only to the rear axle When the driver chooses the front axle can alSo be engaged Further the driver can select between high and low ranges Some part time systems also offer an Auto function that selects between 2 wheel and 4 wheel drive modes according to need without the driver having to do anything Even in these systems however the driver must choose between high and low range In a part time system the occupants may feel or hear something when the front axle engages The transfer case makes more noise in 4 high mode than in 2 high mode And the extra gear reduc Typical part time 4WD transfer case tion of 4 low mode Is prone to making even more noise Part time systems have no differential or other device to allow front and rear propshafts to turn at different rates So if the vehicle is operated in 4 wheel mode on hard pavement driveline binding can cause the tires to crow hop which can be heard and felt This results because all four of the tires do not rotate exactly the Same number of rom either side to side or front to rear Eventually this difference causes the driveline to begin to bind or wind up and one tire or other must temporarily break traction with the pave ment to relieve the pent up energy On unpaved surfaces tires can slip as neces Sary to overcome binding without caus ing crow hop or noise Running the engine with the transfer ca
26. the resistance to relative motion between two surfaces It is pre sent between the threads of a fastener and the threads of a component and between the bolt head and the surface of the component When a threaded fasten er is tightened with a wrench up to 90 of the torque applied to the fastener is necessary to overcome friction Only about 10 of the force is used to hold the components together This is called clamp load Fastener friction and clamp load can be affected by thread cleanliness thread TIP You may want to refer to the earli er article first If necessary you can find a copy of it on the TechLink website at http service gm com The EEST was developed to help you locate tiny leaks in the EVAP system which are defined by OBD 2 as 0 020 inch 0 51 mm or larger It does this by pressurizing the system with vaporized mineral oil which appears as smoke when it escapes from a leak The tool includes a bright light to help you pin point the smoke The EEST is also equipped with a pre cision flowmeter to help you determine whether you ve repaired the leak once you ve located and fixed it Using the Smoke Tester The EEST can be connected to the EVAP system two places depending on instructions in SI These are the under hood EVAP service port with the green cap and the fuel filler neck You can connect at the service port without disturbing any fittings or connec tions in the system TIP If the
27. y stored results If this moves above the fail threshold within the PCM the MIL is turned on and DTC P0442 is set indicat ing a leak larger than 0 020 inch 51 mm S ub Functions The EONV system must perform sev eral sub functions to run the EONV diag nostic Determining Ambient Temperature The EONV must estimate ambient temperature Because EONV occurs at the end of the drive cycle measuring intake air temperature at start up will 5 not suffice The PCM Uses vehicle speed and airflow to calculate an offset value which is subtracted from the intake air temperature to predict ambient temperature Equates the estimated ambient temperature to intake air temperature for a calibrated amount of time after a cold start Refueling Determination The PCM looks for a net increase in fuel level over the course of atest The PCM also looks for an abrupt change in vacuum over a calibrated amount of time as well as changes in fuel level or system pressure that indicate a refueling event The PCM detects refueling events only when the vent is closed If a refueling event is detected the PCM aborts the diagnostic and opens the canister vent The canister vent must be opened quickly to prevent the canister vent from corking closed Corking is a condition when the canister vent sole noid is not opened quickly enough caus ing pressure in the EVAP system to hold the canister vent solenoid closed Rationality T
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