Archive for April 2015

Dimly Lit Service Engine Soon Lamp

On some 2014 Silverado 1500 and Sierra 1500 models and 2015 Silverado, Suburban, Tahoe, Sierra, Yukon and Yukon XL (excluding Denali) models equipped with the mid-level color Instrument Panel Cluster (RPO UDD) and a gas engine, the Service Engine Soon (SES) lamp (Fig. 11) may be dimly illuminated while the engine is running. No DTCs will be set and the dimly illuminated lamp may be noticed only in dark conditions.


F11 IPC lamp r

Fig. 11


This condition affects vehicles built on or around August 1, 2014 – February 28, 2015


Replace the Instrument Panel Cluster using an exchange part ordered after March 20, 2015.


Refer to #PIT5306, TAC Part Restriction – Instrument Panel Cluster, for ordering instructions.


– Thanks to David Goodrow

Driver-side Door Ajar Switch and DIC Message

A Left Rear Door Ajar message may be displayed on the Driver Information Center and the dome lamps may not turn off when the doors are closed on some 2015 Express and Savana vans.


Inspect circuit 1179 for the driver-side 60/40 split door ajar switch being shorted to ground. The driver-side 60/40 split door option (RPO E26) is no longer offered but the door ajar switch wiring is still included in the body wiring harness.


Inspect BCM X6 connector terminal 15 (Fig. 10) for being shorted to ground. If circuit 1179 is shorted to ground, remove the terminal from the BCM connector and tape the circuit back into the harness since the circuit is not needed.


F10 bcm x6 pin 15

Fig. 10


In addition, inspect the wiring around the driver’s front seatbelt retractor at the left B-pillar for any pinching to ensure no other wiring is damaged.


– Thanks to Scott Fibranz

EBCM DTC Diagnostics

When diagnosing a current DTC C1100 SYM02 (Brake Booster Vacuum Sensor Circuit Short to Ground) set on a 2013-2015 Cruze and the diagnostic flow chart in the Service Information leads to replacement of the K17 Electronic Brake Control Module (EBCM), first monitor the Brake Pressure Sensor Data in the scan tool.


The 5 volt reference for the Brake Booster Vacuum Sensor Supply is shared with the Brake Pressure Sensor that is internal to the Brake Pressure Modulator Valve (BPMV).


If the voltage for the Brake Pressure Sensor data is reading constant (1.08 volts without dynamic change; taken from a known vehicle), then it will be necessary to replace the EBCM/BPMV assembly.


Normal Brake Pressure Sensor voltage readings during service brake release and apply should range from 0.5 volt to 3.0 volts.


– Thanks to Christopher Hightower

HD Radio Operation

The AM or FM audio volume may change, mute, echo, cut in and out, repeat broadcast content, or skip intermittently on some 2013-2014 Enclave, Traverse, Acadia; 2013-2015 ATS, SRX, XTS; 2014 Regal, Captiva Sport, Corvette, Impala, Silverado 1500, Sierra 1500; 2014-2015 CTS Sedan (VIN A); 2015 Silverado HD, Tahoe, Suburban (without RPO AVF), Sierra HD, Yukon models (without RPO AVF), and Escalade models. The HD symbol on the radio display may turn on and off when these conditions occur.


These are normal operating conditions when listening to a weak AM or FM HD station.


Each station can have multiple HD stations. For example, if FM 93.7 offers an HD signal, HD1 plays the same audio as the non-HD station and is shown as 93.7 HD on the radio display. A station may have additional HD channels HD2–HD8, which may broadcast different audio/songs. These channel presets would be indicated as 93.7-2 through 93.7-8, if available.


If the HD radio signal reception to channel HD1 is lost, the radio will revert to the main non-HD (analog) radio channel. The audio quality of the analog signal is not as crisp or clear as the HD signal. A weak HD signal may result in the radio switching back and forth between digital and analog signals.


If the HD radio signal loses reception to channels HD2–HD8, the radio does not revert to the non-HD version as it does when the HD signal drops out when listening to HD1. Instead, the radio mutes until the signal can be recovered or until the channel is changed. Skips or echoes may be heard if the HD reception is weak. Digital HD broadcasting signals are weaker than the normal signal strength of the analog station, so HD listening may not deliver the same range as non-HD stations.


HD Radio Setting


If signal reception is causing repeated cycling of the audio between analog and HD, HD may be turned off in the radio settings.


ATS, Corvette, CTS Sedan, Impala, Sierra, Silverado, SRX, Suburban, Tahoe, Yukon models and XTS:

From the home screen on the radio touch screen, select the Audio > Menu > HD Switching Off.


On the CUE system, for example, the Menu option to access the radio settings is on the right side of the Audio page. (Fig. 9)


F09 HD radio

Fig. 9


If the vehicle has a preset saved as an HD station, the HD will automatically turn on when that preset is pressed. It’s recommended to resave the presets as non-HD stations. Once the presets have been saved, the vehicle will need to power down for five minutes to correctly store the new presets.


Acadia, Captiva Sport, Enclave and Traverse:

From the home screen on the radio touch screen, select Now Playing > Menu > HD Disable.


If HD is turned off, selecting a HD preset will not turn HD back on. If HD is off and a HD2-8 station preset is pressed, a message will appear advising to turn on HD. Once the presets have been saved, the vehicle will need to power down for five minutes to correctly store the new presets.


– Thanks to Ryan Dorland

Chattering Wiper Blades

The windshield wiper blades may chatter or skip across the windshield during operation on some 2015 Colorado and Canyon models built between October 1, 2014 and October 31, 2014.


The wiper arm may be twisted in the incorrect direction (Fig. 7), which affects the wiper blade angle and causes the wiper blade to bind during operation. The correct wiper arm angle is shown. (Fig. 8)


If this condition is found, replace the affected wiper arm.


F07 wiper arm incorrect

Fig. 7


F08 wiper arm correct

Fig. 8.


– Thanks to Charles Hensley

Wiring Repair Strategy and the J-38125 Terminal Repair Kit

GM’s global wiring repair strategy is to repair major harnesses (body, engine, instrument panel, forward lamp, etc.) whenever possible and to service minor harnesses (door, seat, steering column, etc.) as assemblies.


This direction was established to reduce the number of individual part numbers needed to service GM vehicles, as even small harnesses can have many different part numbers for the individual connectors and terminals. When new terminals or connectors are released within the major harnesses, they are serviced through the release of connectors, terminated leads, pigtails, etc. and made available through GM Customer Care and Aftersales. If a terminal happens to be a legacy part already available in the J-38125 Terminal Repair Kit, it will be called out in the Service Information.


Additional information about GM’s wiring repair strategy can be found in the updated bulletin #13-00-89-008A.


Repair Parts


There are two sources for wire harness repair parts: the J-38125 Terminal Repair Kit and the dealership parts department.


The J-38125 Terminal Repair Kit (Fig. 4) is a very valuable resource. Many of the terminals that are available in the kit are still in use on current model vehicles. The kit also contains many tools and instructions to service harness connectors and wiring.


TIP: Replenishment tools and terminals for the J-38125 kit are available through Bosch at 1-800-GM-TOOLS (1-800-468-6657).


F04 connector kit

Fig. 4


To download an electronic copy of the J-38125 Terminal Repair Kit Instruction Manual, go to the GM Center of Learning website at Click Resources > STC Training Materials > Service Technical Books. (In Canada, go to Library > Service > Technician Resources in GM GlobalConnect.)


Review the J-38125 Terminal Repair Kit Update Procedure (Fig. 5) to see how to organize and update the Terminal Repair Kit. This large file presents every step in the history of the kit.


F05 connector kit file

Fig. 5


New parts for major harnesses are released as terminated leads, connector kits and connectors. These parts are available only through Customer Care and Aftersales.


Parts Information


The Connector End View section of the Service Information is the source for part number information and where to obtain parts. The harness, connector and terminal part information is found just below the connector end view drawing. (Fig. 6


F06 connector format

Fig. 6


TIP: Use TXL wire to maintain factory specifications for wire harness integrity. TXL wire is available through the Customer Care and Aftersales parts catalog within the Chemical Catalog section. In the Electronic Parts Catalog (EPC), find TXL wire and fuses in the Chemicals – Fuses – Wire – book section.


Connector Repairs


Extensive repair procedures are covered in the Service Information. Go to Power and Signal Distribution > Wiring Systems and Power Management > Diagnostic Information and Procedures.


The information covers wiring and terminal replacement procedures as well as disassembly instructions for various connectors. A listing of required materials to correctly perform wiring repairs also is provided, including splice sleeves and heat shrinking tubing.


– Thanks to Rob Prough

Data Bus Diagnostic Tool Update

A software update to the Data Bus Diagnostic Tool application was released recently. The update includes screen shot functionality to help prevent accidental data loss.


Screen Shots


The application does not have a recording function, but it will save a screen shot any time data might be accidentally lost, such as when closing the application, changing tabs, or clicking the Clear button.


Users also can capture a screen shot at any time by clicking the Screen Shot button. (Fig. 3) These screen shots can be viewed by clicking the View Screenshots button in the Settings menu.


F03 screen shot button

Fig. 3


After 30 days, the screen shots will be automatically removed. To retain screen shots for longer than 30 days, the desired files should be moved to a different location.


Tool Applications


The Data Bus Diagnostic Tool helps identify a starting point in diagnosing faults in a Controller Area Network (CAN) bus by looking at how connectors and wiring are working or not working. The software works with an MDI, a Techline terminal, and an active TIS license.


The application has three sub-applications:

Detected State – Identifies which control modules are responding to diagnostic requests and identifies the physical state of the vehicle bus being diagnosed

Measured Voltage – Provides a low speed voltage trace of the selected bus, CAN LO and CAN HI

Message Monitor – Passively monitors bus activity to help diagnose battery drain conditions


Download the Update


To download the latest software, click the GDS 2 icon on the TIS2Web home page.


If you have any questions about the application, contact the Techline Customer Support Center at 1-800-828-6860 (English) or 1-800-503-3222 (French).


– Thanks to Chris Henley

New AFIT SIDI Kit Adapters and Software

Updates to the Active Fuel Injector Tester (AFIT) Spark Ignited Direct Injection (SIDI) Diagnostic Kit, essential special tool CH- 47976-500A, are currently being released to dealerships.


CH-47976-503 G3 Cable (Fig. 1)


One update includes a new cable (CH-47976-503 G3) and software for fuel system testing on the 2.5L engine (RPO LCV) in the 2015 Colorado and Canyon. The cable plugs into the SIDI Drive & Measurement Unit (DMU).


F01 CH-47976-503 G3

Fig. 1


The pinouts for the ECM used with the 2.5L engine in the Colorado and Canyon are different than the ECM used with the 2.5L engine (RPO LCV) in the Cadillac ATS. The CH-47976-502A cable included in the previously released CH-47976-500A SIDI Diagnostic Kit will not test the 2.5L engine in the Colorado and Canyon and will display an error on the AFIT.


CH-47976-504 G2b Adapter (Fig. 2)


Another update includes a new adapter (CH-47976-504 G2b) and software for use with the AFIT on 2.5L SIDI engines (RPO LKW) in the 2014-2015 Malibu and 2015 Impala with the engine stop/start feature. The new adapter plugs into the CH-47976-502A G2a cable and the three PCM engine harnesses for fuel injection system testing with the AFIT and SIDI DMU.


The adapter is required because stop/start has a secondary circuit that must be energized to crank the engine and build fuel pressure in the fuel rail for the AFIT SIDI tests. The CH-47976-504 adapter re-routes certain circuits so the CH-47976-502A G2a cable can be used.


F02 CH-47976-504 G2b

Fig. 2


Software Updates


Both AFIT updates include a new software download from the GM Dealer Equipment website. Only one software download is needed for both updates. Download the software through the Service Workbench selection of “Essential Tools – Software Updates” in GM GlobalConnect (U.S. only). Open the file and follow the instructions. It will take about 15 minutes to update the AFIT once the download is complete.


If you are experiencing difficulty or haven’t registered with GM Dealer Equipment, go directly to for software updates and additional information.


In Canada, the software is available through the Dealer Equipment Services (DES) Canada website. A link to this site is in the GlobalConnect library under Service/Tools and Processes and Equipment/Essential Tools – Software Updates.


If you need assistance, in the U.S., call 1-800-GM-TOOLS (1-800-468-6657), select option #3, then select option #1, and then select option #2.


– Thanks to Chuck Berecz

Bulletin Review – March 2014

Bulletin Category

Bulletin Number



Body Hardware and Trim


Front Floor Console Rear Ashtray/Bin Door May Not Close

2008-2013 Cadillac CTS

Body and Accessories


Information on Upgrading Certain OnStar® Analog/Digital-Ready Systems to OnStar® Generation 6 Digital-Capable System

2000-2004 Buick LeSabre; 2003-2004 Buick Rendezvous; 2004 Buick Rainier, Regal; 2004-2005 Buick Century; 2002-2004 Cadillac DeVille, Seville; 2003-2004 Cadillac CTS; 2003-2004 Cadillac Escalade Models; 2004-2005 Cadillac SRX, XLR; 2005 Cadillac CTS, STS; 2001-2004 Chevrolet Impala, Monte Carlo; 2002-2004 Chevrolet TrailBlazer Models; 2003-2004 Chevrolet Avalanche, Express, Silverado, Suburban, Tahoe; 2003-2005 Chevrolet Cavalier, Venture; 2004 Chevrolet Colorado; 2004-2005 Chevrolet Malibu, Malibu Maxx; 2005 Chevrolet Cobalt, Corvette, Equinox; 2002-2004 GMC Envoy Models; 2003-2004 GMC Savana, Sierra, Yukon Models; 2004 GMC Canyon; 2001-2003 Oldsmobile Aurora; 2002-2004 Oldsmobile Bravada; 2003-2004 Oldsmobile Silhouette; 2000-2004 Pontiac Bonneville; 2003-2004 Pontiac Aztek; 2003-2005 Pontiac Montana, Sunfire; 2004 Pontiac Grand Prix; 2005 Pontiac G6; 2003-2004 HUMMER H2; 2002-2004 Saturn VUE; 2003-2004 Saturn ION; 2003-2004 Saturn L-Series



Brake Lathe Calibration Procedure

2014 and Prior GM Passenger Cars and Light Duty Trucks

Diagnostic Overview, Starting Point, and Programming


Aftermarket ALDL or DLC Interface Devices Causing Multiple Issues

2006-2016 GM Passenger Cars and Trucks

Diagnostic Overview, Starting Point, and Programming


Control Module Diagnostic Trouble Code(s) (DTC)(s) P0601, P0602, P0603, P0604, P0606, P062F, P1621, P16F3 Shared In Multiple Modules

2015 and Prior GM Passenger Cars and Light Duty Trucks

Driver Information and Entertainment


Language Change for OnStar® System

2015 and Prior GM Passenger Cars and Light Duty Trucks

Driver Information and Entertainment


Transport Mode On Message Displayed in Driver Information Center (DIC) and/or Battery Light is Flashing

2011-2015 Buick Regal; 2012-2015 Buick Verano; 2013-2015 Buick Encore; 2014-2015 Buick LaCrosse; 2010-2015 Cadillac SRX; 2013-2015 Cadillac ATS, XTS; 2014-2015 Cadillac CTS Sedan (VIN A), ELR; 2015 Cadillac Escalade Models; 2010 Chevrolet Camaro; 2011-2015 Chevrolet Cruze, Volt; 2012-2014 Chevrolet Orlando (Canada); 2012-2015 Chevrolet Sonic; 2013-2015 Chevrolet Spark, Trax; 2014 Chevrolet Silverado 1500; 2014-2015 Chevrolet Caprice PPV, Corvette, Impala, Malibu, Spark EV, SS; 2015 Chevrolet City Express, Colorado, Silverado, Suburban, Tahoe; 2014 GMC Sierra 1500; 2015 GMC Canyon, Sierra, Yukon Models, Yukon XL Models



Information on High Feature V6 Timing Chain Kits and Chain Guide Replacements, DTCs P0008, P0009, P0016, P0017, P0018 and/or P0019

2007 Buick Allure (Canada) (RPOs LY7); 2007-2012 Buick LaCrosse (RPOs LY7, LLT, LF1); 2008-2012 Buick Enclave (RPOs LY7, LLT); 2007-2011 Cadillac STS (RPOs LY7, LLT); 2007-2012 Cadillac SRX (RPOs LY7, LAU, LF1, LFX); 2008-2012 Cadillac CTS (RPOs LY7, LP1, LLT, LF1); 2008-2012 Chevrolet Captiva (RPO LY7); 2008-2012 Chevrolet Equinox (RPOs LY7, LF1, LFW); 2008-2012 Chevrolet Malibu (RPO LY7); 2009-2012 Chevrolet Traverse (RPO LLT); 2010-2012 Chevrolet Camaro (RPOs LLT, LFX); 2012 Chevrolet Impala (RPO LFX); 2007-2012 GMC Acadia (RPOs LY7, LLT); 2010-2012 GMC Terrain (RPOs LF1, LFW); 2007-2010 Pontiac G6 (RPO LY7); 2008-2009 Pontiac G8 (RPO LY7); 2008-2009 Pontiac Torrent (RPO LY7); 2007-2009 Saturn AURA (RPO LY7); 2008-2010 Saturn OUTLOOK (RPOs LY7, LLT); 2008-2010 Saturn VUE (RPO LY7)



Information for Installing the Correct Replacement Spin-On Oil Filter When Servicing

2012-2016 Buick Enclave, LaCrosse; 2012 Cadillac SRX ; 2013-2016 Cadillac SRX, XTS; 2012-2013 Chevrolet Captiva (VIN L), Impala; 2012-2016 Chevrolet Equinox, Traverse; 2014-2016 Chevrolet Captiva (VIN L), Impala (VIN W), Impala (VIN (1); 2012-2016 GMC Acadia, Terrain



Information for Repairing Engine Front Cover Oil Leak, Sealing Surface Preparation and Applying RTV Sealant

2006-2015 GM Passenger Cars and Trucks



Diagnostic Tips for Preventing Oil Leaks After Changing Oil and Filter

2008-2015 GM Passenger Cars and Light Duty Trucks

General Information


GM Wiring Repair Strategy Information

2009-2015 GM Passenger Cars and Trucks

General Information


Information for Fleet Vehicles – Ignition Key, Fob and Key Rings Configuration

2014-2015 Buick Enclave, Encore, LaCrosse, Regal, Verano; 2014 Cadillac Escalade, Escalade ESV; 2014 Chevrolet Impala Limited; 2014-2015 Chevrolet Camaro, Caprice PPV, Captiva, Cruze, Equinox, Express, Impala, Malibu, Silverado LD, Silverado HD, Sonic, Spark, Suburban, Tahoe, Traverse, Trax; 2015 Chevrolet City Express, Colorado; 2014-2015 GMC Acadia, Savana, Sierra LD, Sierra HD, Terrain, Yukon Models, Yukon XL Models; 2015 GMC Canyon

Power and Signal Distribution


Installation of Electrical Aftermarket Accessories — Battery, Ignition and Ground Feeds — Do Not Splice into Wiring Harness

2007-2014 Cadillac Escalade Models; 2007-2013 Chevrolet Avalanche, Silverado; 2007-2014 Chevrolet Suburban, Tahoe; 2008-2015 Chevrolet Express; 2014 Chevrolet Silverado 2500/3500; 2007-2013 GMC Sierra Models; 2007-2014 GMC Yukon Models; 2008-2015 GMC Savana; 2014 GMC Sierra 2500/3500



Clunk Noise, Rear Transmission Mount Broken

2014-2015 Cadillac ELR; 2011-2015 Chevrolet Volt




Service Know-How

10215.04D – Emerging Issues

April 9, 2014

To view Emerging Issues seminars:

–   Select Resources > Service Know-How/TECHAssist > Emerging Issues > Searchable Streaming Video; or

–   Select Catalog to search for the course number, and then select View > Take or Continue Course

Installing the Correct Replacement Spin-On Oil Filter

Beginning in 2012, the V6 engine (RPOs LFW, LFX, LLT) available in 2012-2016 Enclave, LaCrosse; 2012 SRX; 2013-2016 SRX, XTS; 2012-2013 Captiva (VIN L), Impala; 2012-2016 Equinox, Traverse; 2014-2016 Captiva (VIN L), Impala (VIN W), Impala (VIN (1); and 2012-2016 Acadia and Terrain (excluding police vehicles with RPO 9C1, 9C3) was redesigned with tighter engine tolerances. The oil pressure was increased to accommodate these tighter tolerances. As a result, the oil filter specifications of the production oil filter and the service oil filter were also improved to meet the new engine requirements.

When servicing these V6 engines, it’s important to use the recommended replacement ACDelco PF63E oil filter (GM #19330000) (Fig. 14) to ensure proper engine oil filtration and engine performance.

F14 PF63E

Fig 14

These V6 engines are factory built with an ACDelco PF64 oil filter, which may be confused with the ACDelco PF48 oil filter because both oil filters have the same appearance and oil can size. However, these two oil filters have different internal specifications. The OEM PF64 oil filter has a much higher bypass valve rating that matches the service oil filter requirement of the PF63E, which was specifically chosen to match the performance demands of these engines.

The ACDelco PF64 oil filter installed by the factory meets the specifications of the ACDelco PF63E, but due to the length of the ACDelco PF63E oil filter can, the engine plant cannot build with it because it currently interferes with the assembly line process.

– Thanks to Randy McCrite

Detent Felt as the Accelerator Pedal is Applied

As the accelerator pedal is applied approximately 3/4 of the way on some 2015 Escalade, Silverado, Sierra and Yukon Denali models equipped with the 8-speed automatic transmission (RPO M5U), a detent/click may be noticed with a feel of increased resistance in the pedal.

The accelerator pedal design has changed for vehicles equipped with the 8-speed automatic transmission. The new accelerator pedal design has a built-in detent position near the last 1/4 of pedal travel to provide tactile feedback to the operator. This design is intended to help minimize transmission downshifting, allowing for improved fuel economy and smoother operation.

Applying the accelerator pedal down to the detent will allow a more relaxed acceleration rate. When pressing the pedal through the detent, the transmission will downshift aggressively, enabling an increased acceleration rate.

Do not replace any parts for this condition. This is a normal operating characteristic of the vehicle and no repair attempts should be performed.

– Thanks to Jim Will

Diagnosis of Various HVAC Conditions

On some 2015 ATS, CTS, XTS, Corvette, Colorado, Canyon, Silverado 1500, Sierra 1500; and 2015 Escalade, Silverado 2500/3500, Sierra 2500/3500, Tahoe, Suburban, and Yukon models with the 2015 mid-year RPO AVF, any of the following HVAC conditions may be present:


• HVAC control panel is inoperative (does not light or respond as expected)

• HVAC controls are stuck in an incorrect operating state (for example, regardless of the temperature setting, it only blows full cold air, or the blower may not respond)

• A/C compressor is inoperative or does not follow commands

• Recirculation is inoperative or does not follow commands

• Rear defogger is inoperative or does not follow commands

• Heated seats are inoperative or do not follow commands (applies to Cadillac and Corvette models only)

• Battery Saver Message is on intermittently or flashing on and off

• Any related HVAC DTCs are set: B0163, B0183, B1405, B0173, B0178, B0509, B0514, B0519, B3583, B3933, B0193, B0208 ,B0223, B0228, B0233, B0408, B0413, B0418, B0423, B0428, B0433, B1395, B3531, B374A, B3782, B393B


If any of these conditions are present, reprogram the K33 HVAC Control Module with the updated calibration available in TIS2Web starting on January 17, 2015. If the HVAC condition(s) are not corrected after reprogramming the HVAC Control Module, perform normal diagnostics following the appropriate Service Information.

– Thanks to Jim Will

Headlamp Performance

On some 2014 Sierra 1500 and 2015 Sierra models, poor headlamp performance may be noticed when driving in very dark rural areas. While the headlamps meet all federal (FMVSS) requirements, some owners may request better headlamp performance.

When addressing headlamp performance conditions, normal diagnostics should be performed first. Verify that all headlamps operate properly, that headlamp adjustment is correct, and that there is not any headlamp mounting damage or concerns with the lens (e.g., haziness, cloudiness). Repair any headlamp conditions. If an owner still has a concern, perform the following calibration and bulb repairs.

Build Dates

For vehicles built before December 23, 2014, at Flint Assembly (11th VIN Digit “F”), before January 13, 2015, at Silao Assembly (11th VIN Digit “G”) or before January 16, 2015, at Ft. Wayne Assembly (11th VIN Digit “Z”), reprogram the BCM with the latest calibration available in TIS2Web starting on January 12, 2015. The new BCM calibration will increase the voltage to the headlamp bulbs in both the low beam and high beam settings.

All vehicles built after these build dates have the new BCM calibration and the BCM reprogramming does not need to be performed.

Headlamp Bulb

Next, replace both headlamp bulbs with updated bulb part number 23342527. Verify the correct bulb is being installed by confirming the correct markings on the bulb as shown: (Fig. 12)

1. 28432 2. HIR2+30

F12 4092123 R

Fig 12

When installing the new headlamp bulbs, do not touch the glass. Make sure the bulbs are fully seated into the headlight housing. If the bulb is not properly installed, it can lead to an incorrect light pattern.

The beam pattern photo (Fig. 13) shows the low beam pattern of a properly installed bulb on a Sierra (one lamp with the opposite lamp blocked) on a wall/aiming screen at 25 feet (7.62 m). Each block division is approximately 10.5 inches (26.67 cm).


F13 4092519

Fig 13

Headlamp Aiming

After bulb replacement, refer to the appropriate Service Information for the Headlamp Aiming procedure.

TIP: The bulb replacement and the calibration change should be performed at the same time. Performing these repairs at the same time will show a dramatic improvement.


– Thanks to Jim Will

Weather Conditions’ Effect on High-Performance Brake Components

Some 2012–2015 Camaro SS, Camaro ZL1; 2013–2016 ATS; 2014–2016 CTS (VIN A); 2014–2015 Camaro Z/28, Caprice PPV, Corvette, and SS models may be hard to move after the vehicle has been parked for a period of time. A crunch sound right before the vehicle starts to move may be heard.

Depending on how long the vehicle has been parked, the weather conditions in which the vehicle was parked, and how recently the vehicle has been washed, the condition may be a simple noise when the vehicle first moves or, at the extreme, the vehicle cannot be moved out of the parking space.

This condition may be due to the brake pads freezing to the vehicle’s rotors. Do not replace any brake components for this condition.

High performance brake components (Fig. 11) have a tendency to lightly bind, often noted as resistance, and then lightly clunk when attempting to move the vehicle forward or rearward after a cold soak. This is usually noticed after parking, when the brakes have been wet, such as when driving in the rain or just after a car wash. This is expected of high performance brakes with high friction pads and does not affect the operation or performance of the brakes.

2015 Chevrolet Camaro Z/28

Fig 11

If a residual roughness is felt when braking, it can be easily cleaned by applying the brakes several times until the roughness is gone. If washing the vehicle prior to long-term storage, it is recommended that the vehicle be driven and the brakes applied several times before storing the vehicle.

– Thanks to Matt Bierlein

HVAC System Operation during a Remote Vehicle Start

The HVAC system, heated seats, and rear defogger operate differently during a remote start on 2015 Colorado and Canyon models equipped with Remote Start (RPO BTV or S6P) depending on which HVAC system is used. Here are the details about system operation during a remote start for each system.


Vehicles Equipped with C68 Auto HVAC System (Fig. 9)


F09 hvac auto

Fig 9

If the ambient air temperature is 50°F (10°C) or lower:

During a Remote Start

• HVAC Mode – Defrost with full blower (blower speed will change as coolant temperature increases).

• Heated Seats – Will turn on with no indication on the buttons. The heated seat option must have first been turned on in the Vehicle Settings menu prior to the remote start event.

• Rear Defogger – Will turn on.


When Ignition Key Transitions to Run

• HVAC Mode – Last setting before ignition key was turned off.

• Heated Seats – Will turn off. Driver will have to turn heated seat back on if heated seat operation is desired.

• Rear Defogger – Stays on until it automatically times out.


If the ambient air temperature is between 50°F (10°C) and 69°F (20°C):

During a Remote Start

• HVAC Mode – Last setting before ignition key was turned off.


When Ignition Key Transitions to Run

• HVAC Mode – Last setting before ignition key was turned off.


If the ambient air temperature is 69°F (20°C) or higher:

During a Remote Start

• HVAC Mode – (Cold) medium to high blower speed


When Ignition Key Transitions to Run

• HVAC Mode – Last setting before ignition key was turned off.



Vehicles Equipped with C67 HVAC System (Fig. 10)


F10 hvac no auto

Fig 10

If the ambient air temperature is 50°F (10°C) or lower:

During a Remote Start

• HVAC Mode – Last setting before ignition key was turned off.

• Heated Seats – Will turn on with no indication on the buttons. The heated seat option must have first been turned on in the Vehicle Settings menu prior to the remote start event.

• Rear Defogger – Will turn on.


When Ignition Key Transitions to Run

• HVAC Mode – Last setting before ignition key was turned off.

• Heated Seats – Will turn off. Driver will have to turn heated seat back on if heated seat operation is desired.

• Rear Defogger – Stays on until it automatically times out.


If the ambient air temperature is 50°F (10°C) or above:

During a Remote Start

• HVAC Mode – Last setting before ignition key is turned off.


– Thanks to Charles Hensley

Reprogramming Procedures for the 8L90 8-Speed Transmission

Several reprogramming procedures must be performed after replacement of some components on the new 8L90 8-speed transmission available on the 2015 Corvette, Silverado, Sierra, Yukon, Yukon XL, and Escalade. These procedures are covered in detail in the appropriate Service Information. In addition, the reprogramming procedures also will be used on other transmission applications in future GM models.


Solenoid Valve Characterization Reprogramming

Characterization reprogramming is a new programming procedure. If characterization is not completed when required, shift quality can be less than optimal and may cause the customer to return with a shift concern.

The solenoids in the 8-speed transmission require unique performance characteristic data in order to function at maximum efficiency. This data is programmed and stored in the vehicle’s Transmission Control Module (TCM). (Fig. 4) When a transmission assembly, TCM, or solenoids are replaced during service, the performance characteristic data for the solenoids must be retrieved from the Techline Information System (TIS) website server (the cloud) and programmed into the TCM.

F04 trans TCM

Fig 4

Reprogramming ensures that the characteristic data relationship is properly matched between the solenoids, valve body, and transmission.


Solenoid Characterization Reprogramming Procedure

1. Document the new Transmission Unique Number (TUN) or Part Unique Number (PUN) as required. 2. Log in to TIS2Web/SPS. 3. Type the Vehicle Identification Number (VIN). 4. Select Transmission Control Module – MCVM Operations. (Fig. 5)


F05 capture4 R

Fig 5

5. Select the applicable service procedure performed — currently only replacing transmissions (Replace Transmission button) and replacing the TCM (Refresh Characterization button) (Fig. 6) are allowed — and provide the necessary TUN or PUN. (Fig. 7)


F06 capture 5

 Fig 6

F07 capture 6

Fig 7

At this point, the system will read the VIN from the Engine Control Module (ECM) using the Multiple Diagnostic Interface (MDI) and then retrieve the applicable genealogy data tree for the given TUN/PUN from the cloud. This data tree accesses the original characterization data so that it may be updated with the new component information. The TCM is updated with the correct solenoid characterization data, and the cloud is updated with the new genealogy relationship.


Transmission Service Fast Learn

The Transmission Service Fast Learn procedure has been a required programming procedure on some current 6-speed transmissions.

Transmission Service Fast Learn is a procedure that is performed after any 8-speed transmission repair. The procedure performs a series of tests which allow the TCM to learn individual clutch apply pressures. These learn pressure values are used by the TCM for clutch control and timing of shifts. A scan tool is used to perform the Transmission Service Fast Learn procedure.

The Transmission Service Fast Learn procedure must be performed when any of the following repairs has been made to the transmission:

• Pressure regulating solenoid replacement

• Valve body repair or replacement

• Any service/repair in response to a shift quality concern

• Any internal transmission service, repair, overhaul, or replacement

• Torque converter replacement

• TCM replacement

• Transmission assembly replacement


Failure to perform the procedure may result in poor transmission performance, DTCs being set, or customer dissatisfaction.


Transmission Service Fast Learn Procedure

1. If a pressure regulating solenoid, TCM or transmission assembly was replaced, perform the Solenoid Valve Characterization Reprogramming. 2. With the ignition on, clear the DTCs with a scan tool. 3. Turn the ignition off and make sure all vehicle systems turn off. It may take up to two minutes for all vehicle control modules to power down.

TIP: If the transmission fluid temperature is not between 167°F (75°C) and 185°F (85°C), the scan tool will not allow you to perform the Service Fast Learn procedure.

4. With the engine running, shift the transmission to the Drive position with the brake applied. Perform the Service Fast Learn procedure with a scan tool. In GDS 2, go to Module Diagnostics > Transmission Control Module > Configuration/Reset Functions > 5. Transmission Service Fast Learn. (Fig. 8) Follow the instructions on the scan tool. Turn the Ignition off for two minutes.


F08 Capture 1

Fig 8

– Thanks to Mike Johnston

All-New 8L90 8-Speed Automatic Transmission

During the development of the all-new, GM-developed Hydra-Matic 8L90 8-speed automatic transmission (RPO M5U) (Fig 1), offered on the 2015 Corvette, Silverado, Sierra, Yukon, Yukon XL, and Escalade, more than 550 computer-aided engineering analyses were made to ensure strength, durability, performance and refinement.

In the Corvette Stingray, the results are a paddle-shift that delivers world-class shift times rivaling the best dual-clutch designs. While in the Silverado and Sierra, the new transmission delivers 11 percent greater torque capacity than the 6L80 6-speed transmission it replaces.

2015 Hydra-Matic 8L90 (M5U) Eight-Speed RWD Auto Transaxle for C

Fig 1

TIP: The transmission is currently on exchange through the GM Product Quality Center (PQC). No transmission repairs, internal or external, are allowed at this time. If diagnosis has determined the need for any repair to the transmission, contact the PQC to discuss the information/diagnostics that led to the need to repair the transmission assembly before performing any repairs.



The eight speed ratios of the 8-speed transmission are generated using four simple planetary gear sets, two brake clutches, and three rotating clutches. (Fig. 2) The resultant on-axis transmission architecture utilizes a “squashed” torque converter, an off-axis pump and four close coupled gear sets. The three rotating clutches have been located forward of the gear sets to minimize the length of oil feeds which provides for enhanced shift response. There are different variants of the transmission, all based on torque capacity. Architecture is common between the variants, and component differences are primarily related to size.

2015 Hydra-Matic 8L90 (M5U) Eight Speed RWD Automatic Transaxle

Fig 2

The Transmission Control Module (TCM) is externally mounted. It makes use of three speed sensors that provide for enhanced shift response and accuracy. The TCM receives and monitors various electronic sensor inputs to execute hundreds of calculations and commands every 6.25 milliseconds.

The 4-element torque converter contains a pump, a turbine, a pressure plate splined to the turbine, and a stator assembly.

The hydraulic system primarily consists of an off-axis chain-driven binary vane-type pump located in the valve body, and two control valve body assemblies. (Fig. 3)

2015 Hydra-Matic 8L90 (M5U) Eight Speed RWD Automatic Transaxle

Fig 3

Clutch compensators are fed by lubrication oil rather than the dedicated and regulated feed design of the 6L80 transmission. This design reduces the number of rotating oil seals and oil channels within the turbine shaft and adds the capability of rapid discharge of oil in the compensators during clutch apply for greater control.


Transmission Control Module

The TCM has one 66-way connector to interface with vehicle electrical system, transmission assembly and other vehicle control modules. Based upon the calibrations and input information the TCM receives, it always has final authority of when to allow an upshift or downshift whether in manual mode operation or in drive position for automatic shifting.


Transmission Solenoid Valves

The 8L90 transmission contains a total of nine individual solenoids in the lower control valve body assembly. Seven of the nine solenoid valves are used to control pressure regulation and direction of transmission fluid and the two on/off solenoid valves are only used to direct transmission fluid.

There are three variations of pressure regulating solenoid valves used on this transmission: high pressure normally low; high pressure normally high; and low pressure normally high, variable force.


• High Pressure indicates the solenoid valve is controlling or directing line pressure.

• Low Pressure indicates the solenoid valve is directing a pressurized fluid that is less than line pressure.

• Normally Low is when no current is applied to the solenoid valve coil, the variable restriction is closed, resulting in no or low pressure.

• Normally High is when no current is applied to the solenoid valve coil, the variable restriction is open, resulting in maximum or high pressure.

• The Variable Force Solenoid Valve can increase or decrease the amount of pressurized fluid based on the amount of current applied to solenoid valve coil.


Pressure Regulating Solenoid Valves

Pressure regulating solenoid valves regulate hydraulic fluid pressure based on current flow through the solenoid valve coil windings. They are operated by a 12V high side driver and a low side driver, both internal to the TCM. Current is controlled by turning the low side on and off. If the TCM detects a malfunction, it turns off the high side driver to that solenoid and sets a DTC.

Transmission control solenoid valves 2, 3, and 7 are high pressure, normally low, variable force solenoid valves; increased current results in increased fluid pressure.

Transmission control solenoid valves 1, 5, and 6 are low pressure, normally high, variable force solenoid valves; increased current results in a decrease in fluid pressure.

Transmission control solenoid valve 4 is a high pressure, normally high, variable force solenoid valve; increased current results in a decrease in fluid pressure.

Transmission control solenoid valves 8 and 9 are normally low, on/off solenoids. These solenoids only direct hydraulic fluid pressure when commanded on.


Solenoid Characterization

Transmission control solenoid valves 1–7 are pressure regulating valves. Each individual solenoid valve is tested after assembly to determine the output fluid pressure at certain electrical current values, applied to coil windings.

The current versus pressure data points are assigned a file number, which is marked on the solenoid valve housing end. The performance data file is stored on the Techline Information System (TIS) website and is programmed and stored in the vehicle’s TCM.

TIP: Replacing any of the following components will require the TCM to be programmed with the new or existing solenoid valve performance data.

TCM – Program the new TCM with the existing solenoid data files stored on the TIS website for all seven pressure regulating solenoid valves

One or more solenoid valves – Program the TCM with the new data file for only the individual pressure regulating solenoid valves that were replaced

Lower Control Valve Body Assembly with Solenoid Valves – Program the TCM with the new data files stored on the TIS website for all pressure regulating solenoid valves

Transmission Assembly – Program the TCM with the new data files stored on the TIS website for all pressure regulating solenoid valves


Speed Sensors

The TCM uses the input speed sensor signal along with the intermediate and output speed sensor signals to determine transmission line pressure, shift patterns, torque converter clutch slip speed and the correct gear ratio.

The speed sensors are two wire hall-effect type sensors. The TCM supplies a 9V signal circuit and a low reference circuit to the input speed sensor. The speed sensor produces a square wave signal.


Transmission Fluid Temperature Sensor

The transmission fluid temperature sensor measures the temperature of the fluid in the transmission fluid pan. It is a 2-wire negative temperature coefficient thermistor. The TCM supplies a 5V signal circuit and a low reference circuit to the transmission fluid temperature sensor.

The transmission fluid temperature sensor is part of the transmission internal wire harness assembly and has no serviceable parts. If the transmission fluid temperature sensor is faulty, the internal transmission wire harness assembly must be replaced.


Internal Mode Switch (IMS)

The IMS contains six separate switches in one assembly. One mechanical switch circuit is for the Park/Neutral position switch, which is used for engine starting. The other five electronic switches are called the transmission range switches and are used to indicate the current gear position the vehicle operator has selected. The IMS switch assembly is mounted on the interior left side of the transmission case.


– Thanks to Mike Johnston

  • [+]2017
  • [+]2016
  • [+]2015
  • [+]2014