Archive for April 2012
When servicing a vehicle, any control module that wakes up with a circuit disconnected may set a current DTC, which will go into history once the circuit is reconnected. This condition is related to how the vehicle power mode works with different control modules with the key On vs. the key Off. These DTCs often are set inadvertently by waking a control module when opening a door and will not clear until the proper self-test has been completed, which depends on operating conditions being met.
Here’s an example of how a history DTC could be set on 2010-2013 vehicles that require the GDS 2 scan tool for vehicle communication (2010-2012 LaCrosse; 2011-2012 Regal; 2012 Verano; 2010-2012 SRX; 2010-2012 Camaro, Equinox; 2011-2012 Cruze, Volt; 2012 Sonic; 2013 Malibu, and 2010-2012 Terrain). A history DTC P0113 (Intake Air Temperature Sensor Circuit High Voltage) may be stored immediately after vehicle service if the Engine Control Module (ECM) wakes up (activates) while a 5-volt reference sensor is unplugged and the ignition is Off.
If a technician were to leave the Intake Air Temperature/Mass Air Flow (IAT/MAF) sensor disconnected and open the driver’s door with the battery connected, ignition Off, and the ECM “asleep,” the Body Control Module (BCM) would wake up the ECM, causing the ECM to sense the open IAT sensor and set a current DTC P0113. After the IAT sensor is reconnected, the DTC status will clear as a current DTC, but it will still be in stored in history.
This is just one example. There are others that may occur when other sensors are disconnected and a control module wakes up.
If this condition occurs during unrelated vehicle repairs, do not replace any parts. Simply clear the DTCs and ensure that they do not reset.
If current DTCs are stored, this information does not apply and the appropriate Service Information diagnostics should be followed.
- Thanks to James Parkhurst
An intermittent no crank or start-stall condition with the security light illuminated on some 2008-2012 Enclave; 2010-2012 LaCrosse; 2012 Verano, Regal; 2008-2012 CTS; 2007-2011 DTS, STS; 2011-2012 Cruze; 2012 Sonic; 2009-2012 Traverse; 2007-2012 Acadia; and 2007-2010 Outlook models may be due to Radio Frequency Interference (RFI) with the vehicle security system.
DTCs B3055 (No Transponder Modulation or No Transponder), B3060 (Unprogrammed Transponder Identification Code Received), and/or B3935 (Transponder Authentication Error) may be set in history. In most cases, the condition cannot be duplicated.
On vehicles equipped with Passive Entry/Passive Start (RPOs ATH, BTH), it is also possible the vehicle may have a condition where the passive entry is inoperative and/or there is a No Fob Detected message, but the vehicle will start with the key fob placed in the fob pocket.
Do not replace any parts for this condition prior to duplicating the condition.
With the advancements in today’s technology, there has been a great increase in the number of Radio Frequency Identification Devices (RFID) found across many communities, businesses, and automobiles. It is possible that another RFID device may interfere with the Passkey system. The range of the interference can vary based on the strength of the RFID, which may affect the key-to-exciter module communication. The most common devices found are: vehicle immobilizer keys from other vehicles, keyless access transmitters from other vehicles, highway/bridge toll passes, gate passes, community/parking access cards, fuel station speed passes, and building access swipe cards/transponder devices. (Fig. 6)
In addition, verify the vehicle owner is not inducing the concern by flipping the key while cranking the engine. Refer to #PIT5030 for more information.
For vehicles with Passive Entry/Passive Start, it is possible to get RFI from transponders or other frequency-emitting devices in the area. An aftermarket RFI meter can be used as an aid to locate the stray RFI signals. (Fig. 7)
TIP: Direct owners to the appropriate section in their Owner Manuals for information about how a device complies with Part 15 of the FCC Rules. Examples of where this information may be found depends on the model and/or year, but in most manuals, refer to the Immobilizer Operation, Keyless Entry, Keyless Access, or Radio Frequency Statement sections.
- Thanks to Ernest Haller
Some 2011-2012 Volts may have a no crank condition with a Waiting to Initialize message displayed on the Driver Information Center. The condition also may be accompanied by DTC P0AFA (Hybrid/EV Battery System Voltage Low) set in the Hybrid Powertrain Control Module 2 (HPCM 2).
This condition may be seen after the following:
• An extremely low or dead 12-volt battery. • After removing the manual disconnect • After replacing a major component, such as the 300V battery, drive unit, drive motor control module (TPIM), etc. • After SPS programming several modules at one time or after major reprogramming events • After an airbag deployment
If this no crank condition with the Waiting to Initialize message is observed along with one of the symptoms listed above, follow this procedure:
1) Make sure the 12-volt battery is fully charged.
2) Connect GDS 2 and build the vehicle, select Module Diagnostics/Hybrid Powertrain Control Module/Control Functions, and then select Check High Voltage System Related DTCs. (Fig. 4) Read through all the DTCs. When finished, back out to the previous screen.
3) Select Clear Secured High Voltage DTCs (Fig. 5) in the HPCM and hit the Reset button on the bottom of the screen. Wait 45 seconds before exiting the screen.
4) Next, select Hybrid Powertrain Control Module 2/Control Functions and then select Check High Voltage System Related DTCs. Read through all the DTCs. When finished, back out to the previous screen.
5) Now select Clear Secured High Voltage DTCs in the HPCM 2 and hit the Reset button on the bottom of the screen. Wait 45 seconds before exiting the screen.
6) Disconnect the MDI from the vehicle and turn off the ignition. Close all vehicle doors and allow the vehicle to go into a sleep mode for three minutes.
7) Disconnect the 12-volt positive and negative battery cables and touch the battery cables together. Re-install after 15 seconds.
8) Attempt to start the vehicle after a three minute waiting period.
9) If vehicle still doesn’t crank, follow the appropriate Service Information diagnostics.
- Thanks to Paul Radzwilowicz
Recently in TechLink, [link to March 2012 article] the importance of double-checking wheel alignment specifications was highlighted. The only recommended source of current, accurate wheel alignment specifications (both targets and tolerances) is the Service Information. The specifications indicated on the wheel alignment rack should always be verified with the appropriate Service Information.
In the first quarter of 2012, the following models had updated/changed wheel alignment specifications:
Check the alignment specifications for these models in the appropriate Service Information against the alignment machine specifications before performing an alignment. Be sure to take into account all related option content on the vehicle, including tire and suspension RPOs. These updated specifications most likely will not be included in the latest specifications from alignment machine manufacturers.
Not using the correct specifications as shown in the Service Information may result in a warranty claim being subject to review.
- Thanks to David MacGillis
ACDelco recently made changes to several fuel modules to further enhance their performance. The timing of the changes for each part number has varied, but implementation of the changes began last summer.
When replacing a fuel module, you may have noticed some of these new design changes:
• The pump changed from a Gerotor pump to a Generation 4 Turbine pump, which is quieter and more durable. (Fig. 3, A) • The module plastic material changed to a more fuel resistant Acetyl plastic that provides an improved high alcohol fuel tolerance. (Fig. 3, B) • Guide rods were reduced from 3 to 2, which retains proper alignment while reducing pinching. (Fig. 3, C) • Jet pump has been added to help maintain fuel in the reservoir. (Fig. 3, D) • The float material is more fuel resistant for longer life. (Fig. 3, E) • The external strainer has been moved inside the fuel module to help reduce the chance of puncture. (Fig. 3, F) • Some float arms and pivot points have changed; however, the fuel level sensor output has not changed. (Fig. 3, G)
While the appearance of the fuel modules has changed, the fit, form and function has not. In addition, the part numbers did not change.
To address any concerns regarding the product changes, a special notice is included inside each box explaining that the module has undergone changes.
- Thanks to Dan Carter
During the 2012 model year, a seal change and an axle shaft change were made on the rear axle output seals on AWD versions of the 2012 LaCrosse and SRX.
The old style seal is black and the axle shaft that mates with it does not have a slinger. (Fig. 1) The black (first design) seal is GM P/N 20986535.
The new style seal material is yellow and it mates with an axle shaft that has an integral slinger. (Fig. 2) The yellow (second design) seal is GM P/N 22845699.
TIP: Do not mix the different seals and axle shafts. Installing first design seals with the second design axle shafts OR installing second design seals with first design axles shafts will result in a leak.
If a rear axle component is incorrectly ordered and it comes with a seal that is incompatible with the vehicle’s axle shafts, it is not necessary to return the part. Simply get the axle seal that matches the existing axle shafts and replace the seal(s) using the seal replacement procedure in the appropriate Service Information.
- Thanks to David MacGillis
The GM TechLink website is sporting a new look this month. It’s just one part of the updated and revised TechLink, which has been redesigned to enhance functionality and ease of use.
Along with the new look, the site has been reorganized with each article presented on the Home page, making it easy to select one article or to “flip through” all articles. In addition, the blog feature now provides users the opportunity to offer feedback on a topic without registering on the site. Users must still sign in with their name.
The printable version in a pdf format covering all the articles will be available each month. Previous issues also will be available in the pdf archive. TechLink will continue to be available in French and Spanish as well.
Finally, there will be more of TechLink. The website will be updated twice each month — at the beginning of the month and mid-month. To get started, simply click an article on the Home page.
TechLink staff (left to right)
Adam Monblatt, Diana Sancya, Mark Spencer, Lisa Scott
When owners bring in their vehicles for service regarding connecting a device to the audio system, a new service tool is now available to help with diagnosis. The Multi-Media Interface Tester (MIT), EL-50334-20, is designed to perform pass or fail testing on the Bluetooth®, USB and auxiliary jack connections.
The MIT outputs four distinct audio files to test the Bluetooth, AUX/Line-In, and USB functions of the audio system. The operation of each test function is confirmed by a confirmation message played back through the vehicle’s audio system.
The MIT, for example, can test the ability of the infotainment system or OnStar system to pair a device. It also can place a test call and confirm that the Bluetooth system is working properly.
MIT test modes include:
• Bluetooth Test Modes
- Pairs with vehicle (Hands-free cell phone)
- Places a simulated test call
- Confirmation message of proper Bluetooth system operation
- Streaming audio from a mobile device (Test mode currently not available for Camaro and Sonic)
- Confirmation message of proper Bluetooth streaming audio system operation
• USB Test Modes:
- Connection detection
- Confirmation message of proper USB system operation
• Auxiliary Jack Test Modes:
- Connection detection
- Confirmation message of proper auxiliary jack system operation
The MIT is powered by a USB cable. (Fig. 2) The included USB power adapter can be used to power the MIT on vehicles that do not have a USB port. The included RCA adapter cable is used to test the audio (Line-In) functions on vehicles using that connection instead of the 3.5mm auxiliary jack.
The user’s guide for the MIT is available on the tool in a pdf format. To access the pdf, connect the USB cord from the MIT into a computer and press the TEST SELECTOR button until the USB LED indicator illuminates. The computer will recognize a new device and allow access to the folder where the user’s guide is stored. The guide can be viewed or printed from the folder.
- Thanks to Katul Patel, Robert Hrabak, Paul Gallo and Lana Fawaz
When performing a transmission oil cooler flow check and flush test on the 2003-2010 Vibe, 2002-2007 VUE, 2003-2004 ION and 2008-2009 Astra, essential tool J-45096, Transflow Transmission Cooler Flusher, should be used. (Fig. 3) This procedure applies to both automatic and manual transmissions that do not use DEXRON®-III or DEXRON®-VI transmission fluid.
A plugged or restricted transmission oil cooler and pipes may lead to insufficient transmission lubrication, elevated operating temperatures, and ultimately, premature transmission failure. To prevent this, follow the transmission oil cooler flow check and flush test procedures outlined in the appropriate Service Information and #PI0537.
The procedure involves:
• Machine set-up
• Determining the minimum flow rate
• Back flushing
• Forward flushing
• Flow testing
• Code recording
• Clean up
The J-45096 transmission oil cooling system flush and flow test tool replaces other cooler flushing tools. The J-45096 tool is a self-contained unit using a 12-volt flow meter, shop air supply and DEXRON-VI automatic transmission fluid (ATF).
TIP: Use only DEXRON-VI automatic transmission fluid in the J-45096 tool. While the transmission fluid requirement for the listed vehicles is different than DEXRON-VI, flushing the cooler with DEXRON-VI is an acceptable service procedure. Very little fluid remains in the cooler after the flush procedure and the residual DEXRON-VI ATF in the cooler is compatible with the listed vehicles’ transmission fluid.
When using the tool in the flush mode, ATF is cycled through the transmission oil cooling system. High-pressure air is automatically injected into the fluid stream, adding agitation to the ATF oil, to help remove contaminated oil and debris.
In the flow mode, the electronic flow meter measures the flow capability of the transmission oil cooling system. The display indicates the ATF oil flow rate in gallons per minute (GPM) along with the amount of ATF in the supply vessel, supply vessel ATF temperature, machine cycles and the operating mode. The required minimum ATF oil flow rate reading is directly related to the supply oil temperature.
In the code mode, a random, encrypted code is generated that can be used for verification of flow test results. After completing the flush and flow testing, the testing flow rate (in GPM), temperature, cycle number and seven-digit flow code must be recorded on the repair order.
Current essential cooler line adapters are used to connect the J-45096 to the transmission oil cooler lines, which enables the tool to adapt to most GM passenger cars and light-duty trucks. If an adapter is not available, one can be made using a barbed hose connector and a rubber hose obtained locally.
For information about vehicles with automatic transmissions that use DEXRON-III or DEXRON-VI transmission fluid, refer to Bulletin #02-07-30-052H.
- Thanks to Dave Peacy and Mark Kevnick
Today’s GM Service Information (SI) is typically authored in one location and then translated for use in many different countries. This requires resources and input from all GM global regions to determine the best service strategies and special tools needed to properly repair GM vehicles. The goal is to have common service procedures and special tools when new vehicles are launched.
Since the 2003 model year, all new special tools have used a global tool number that begins with a prefix of two alpha characters followed by five numbers (e.g. EN-49010 – Flywheel Holder). There are six tool groups:
EL Electrical, SIR
BO Body, Frame, Trim
Tools created before the global tool numbering system was implemented in 2003 are referred to as legacy tools. They may have several different numbering formats depending upon which GM global region created the tool. Tools with a single “J” prefix identify tools developed primarily in North America, whereas a “KM” prefix indicates the tools were developed primarily in Europe. Both are followed by 3, 4, or 5 numerals. A suffix indicates the tool has been revised, superseded or is part of a kit.
Every attempt is made to minimize the need for new essential tools each model year by using existing tools from prior models and other GM global regions. Legacy tools within each GM global region are reviewed for each new vehicle launch prior to the development of new tools. This is why it’s important to never discard old special tools as additional applications may be found to avoid new tool releases.
If a legacy tool from one GM global region (J or KM) is found to work on a new vehicle, it can be used in other GM global regions. In these cases, a duplicate Administrative Tool Reference Number is created to add the global tool prefix to the legacy numbering. For example, chassis tool KM-12345 becomes CH-12345. The Administrative Tool Reference Number is used in the SI procedure as a reference. The numbering sequence does not change, only the prefix. This allows the use of the same procedure in all GM global regions with the intent to achieve consistency in special tool numbering.
When working within SI, if you see a tool number that is not familiar to you, click the Special Tools link in the procedure. This will take you to the Special Tools table, where the local number is listed along with all the regional tool numbers associated with that tool. These special tool numbers may have originated in other GM global regions, such Europe, Korea, Australia or Brazil. Choose the number that is recognized in your location. For North America, these will typically be the J-numbered tools. Each tool will be physically marked with the released tool number. Tools are not marked with the SI Administrative Tool Reference Number.
TIP: When ordering tools from SPX (Kent-Moore) or viewing the SPX website, use the entire legacy tool (actual) number and not the SI Administrative Tool Reference Number.
For more information about the special tool numbering system, refer to Bulletin #03-00-89-005A.
Later this year, a new special tool reference strategy that eliminates the need for the Administrative Tool Reference Numbers in SI will be implemented. Thanks for your patience during the transition to this improved methodology.
- Thanks to Russ Dobson and Bob Scherer
A Service Power Steering message may be displayed intermittently on the Driver Information Center of the 2012 Verano while driving. During diagnosis, there may not be any communication with the Power Steering Control Module (PSCM). Plus, DTC U0131 (Lost Communication with Power Steering Control Module) may be set in other control modules.
TIP: When using GDS 2, if a “Power Steering Not Supported” message is received, delete the vehicle session from GDS 2 and reload the vehicle to verify the correct RPOs were selected when building the vehicle.
Inspect for a loose X5 connection at the Underhood Bussed Electrical Center (UBEC) 80 amp fuse for the PSCM. (Fig. 4) If the X5 connection is found to be loose, repair as necessary and verify repairs.
- Thanks to Bryan Brunner
What’s the cost of not following the proper diagnostic procedures? In one case, a new transmission.
Strategy-Based Diagnosis has been emphasized for a long time. A recent real-life example illustrates what happens when a technician doesn’t perform Step 5 – Check for related Bulletins, Recalls and Preliminary Information (PI), or when that information isn’t followed or is disregarded.
A 2011 Avalanche was brought in to a dealership with an illuminated Check Engine light and an erratically shifting and jerking transmission. This vehicle is equipped with a 6L80 automatic transmission.
After a road test, the technician found that the line pressure was erratic. He then dropped the transmission pan and, during inspection, found that the transmission fluid filter was split along the seam. The filter was replaced and the transmission was refilled with fluid.
When the vehicle returned with the same condition, the filter was replaced again. After calling TAC and getting additional information (#PI 0488A) about inspecting the pump when a cracked or split filter is found, the filter was replaced once more; this time with an aftermarket filter.
#PI0488A covers a no forward, no reverse or slipping condition on the 6L80 and 6L90 6-speed automatic transmission on some 2010-2012 CTS V, Escalade models, Avalanche, Camaro, Corvette, Express, Silverado, Suburban, Tahoe, Savana, Sierra, Yukon and Yukon XL models. It points out that if the filter is cracked or split (Fig. 5), the fluid pump should be disassembled and inspected for possible damage, such as a scored pump rotor or pump vanes, scored pump cover or pump rotor pocket, or a cracked pump slide. The transmission also should be evaluated for any possible distress to the clutches.
Upon inspection, the first, and obvious, repair is to replace the damaged filter. The second, and less obvious, repair is to inspect the pump. But if information in a PI doesn’t make sense, it should not be ignored, which in this case, it was.
The damaged pump can send a high pressure fluid spike down the filter neck on a cold start, resulting in the filter body cracking or the filter seam splitting. The filter itself is not defective. If the damaged pump isn’t replaced in time, it can lead to clutch damage due to low line pressure and possible transmission replacement.
After a total of four filter replacements and further road testing, a replacement transmission was ordered. Had the technician done the proper Service Information research when the first damaged filter had been found, even if the information in the PI didn’t appear to make sense at first glance, following the PI and checking the pump would have lead to a quick and correct repair. Repairing the pump would have been much less expensive than replacing the transmission.
The final result of this repair is that GM did not pay for the transmission replacement. It was a costly mistake and an unnecessary repair.
Remember to follow Strategy-Based Diagnosis and check the Service Information for the latest Bulletins and PIs. These resources have been put in place to help avoid expensive and unnecessary repairs that waste technicians’ time, lead to needless parts replacement, drive up warranty costs, and cause customer dissatisfaction.
- Thanks to Dave Peacy
During normal diagnosis of a 2011-2012 Express, Silverado, Savana, or Sierra equipped with the 6.6L Duramax diesel engine (RPOs LGH, LML), it may be noticed that the Exhaust Gas Temperature sensor four (EGT 4) is reading incorrectly. This may be noticed with or without any EGT DTCs.
If a 2012 model year vehicle is inadvertently built as a 2011 model year vehicle, some of the data parameters on the Tech 2 may be incorrect. If this is encountered, make sure all the vehicle identification information has been input correctly.
A 2012 diesel-equipped vehicle built as a 2011 vehicle will show EGT 4 at or near 1000° C/1850° F. If a reading of 1000° C/1850° F has been found on EGT 4, do not replace the sensor until after checking that the vehicle is built correctly on the Tech 2.
If an incorrect reading is found, and the vehicle identification has been input correctly, continue with the appropriate Service Information diagnostic for the symptom or DTC.
- Thanks to Donald Langer
An Exhaust Fluid Quality Poor message displayed on the Driver Information Center of the 2012 Express, Silverado, Savana, and Sierra equipped with the 6.6L Duramax diesel engine (RPOs LGH, LML) notifies the driver that the Engine Control Module (ECM) has detected a drop in the NOx reduction efficiency of the Selective Catalyst Reduction (SCR) system. The Exhaust Fluid Quality Poor message may be displayed without any set DTCs.
An Exhaust Fluid Quality Poor message does not always mean the fluid is contaminated or needs to be changed. The J-26568 Coolant and Battery Fluid Tester can be used to test the fluid before deciding to discard it.
1. Collect a DEF sample of about 150 ml (5 oz.) from the DEF tank in a clear container. The DEF sample should be clear with no obvious coloration when held up to a light.
As clean DEF is clear, contamination by any common automotive fluids will cause the DEF to exhibit a trace of color associated with a specific contaminate.
• Windshield washer solvent – orange, purple or blue
• Engine coolant – orange or green
• Engine oil – brown
• Transmission fluid – red or brown
• Diesel fuel – clear, yellow, green, red or brown
2. Observe the DEF sample. It should have an ammonia smell. Clear fluid without the presence of an ammonia odor may indicate water or DEF diluted with water.
3. Measure the refractive index of the DEF sample using the J-26568 Tester. The refractive index of pure DEF should be between 1.310–1.3843 at 20° C (68° F). If not within the specified range, drain the remaining DEF and refill the tank with fresh DEF.
4. If the DEF tests normal, perform the DEF Quality test with a scan tool. The DEF Quality test should pass. If the test fails, replace the DEF.
If an Exhaust Fluid Quality Poor message is displayed without any set DTCs, diagnose the condition using the appropriate Service Information diagnostics for DTC P20EE (NOx Catalyst Efficiency Below Threshold)/P2BAD (Exhaust NOx Concentration High–Unknown Reason). After making repairs, use the DTC P20EE/P2BAD repair verification and/or SI Document number 2614265 titled “Reductant Fluid Quality Test (with or without DTCs)” to evaluate and clear the Exhaust Fluid Quality Poor message.
- Thanks to Donald Langer
The Flex Fuel E85 badge commonly found on the rear of many flex fuel vehicles has been changed on the 2012 Equinox and Terrain. The liftgate Flex Fuel badge has been replaced with a Flex Fuel decal located on the fixed rear quarter glass.
The VIN breakpoints are:
(Identified by a 6 as the 11th digit of the VIN)
Build Date: February 22, 2012
(Identified by a 1 as the 11th digit of the VIN)
Build Date: March 5, 2012
Build Date: February 22, 2012
To ensure all vehicles get the E85 Flex Fuel identifier, during a 48 hour change-over period, a number of vehicles were produced with both the badge (Fig. 6) and the window decal. (Fig. 7) Vehicles built on or after the build dates are built with the E85 window decal.
If owners notice the E85 Flex Fuel badge is missing from the liftgate, point out the decal located on the fixed rear quarter glass. Do not order or install an E85 Flex Fuel badge on the liftgate.
- Thanks to Doug Daugherty
To discourage unqualified individuals from attempting to repair the high-voltage battery cooling system, Volts built after January 27, 2012 (VIN# CU113809 and higher) are shipped with an anti-tamper bracket assembly in the rear compartment. The bracket is to be installed at the dealership during Pre-Delivery Inspection (PDI). The PDI form has been updated with this new step.
The anti-tamper bracket assembly (Fig. 8.) must be installed to the passenger-side of the high-voltage battery/power electronics coolant surge tank assembly after the coolant level is adjusted.
Coolant Level Adjustment
After completion of the PDI road test, adjust the coolant level to the top of the seam in the middle of the surge tank. (Fig. 9) This slight overfill condition will protect for the purging of trace amounts of air in the system that wasn’t purged during the road test.
Final adjustment of the coolant level must be followed by the installation of the anti-tamper bracket. The anti-tamper bracket R&I procedure can be found in the Service Information. Installation can be considerably streamlined with the use of a 10mm ratcheting box-wrench placed under the radiator upper cross-bar. (Fig. 10)
- Thanks to Scott Jesnig
The GM Accessory and Camaro Transformer high wing spoiler Center High Mount Stop Lamp (CHMSL) may develop cracks in the area around the fasteners on some 2010-2012 Camaros. (Fig. 11) If this condition is observed, replace the CHSML only; it is not necessary to replace the spoiler.
The CHMSL kit is currently available through the Warranty Parts Center. Refer to #PI0685 for complete details.
The cracked CHSML can be removed from the spoiler by removing the caps that cover the screws, and then removing the screws. Some force may be necessary. Unplug the CHSML from the wiring harness and connect the new CHSML.
The kit includes washers to be used with the new CHMSL fasteners. It is recommended to use Butyl to hold the washers in place during installation of the CHSML. (Fig. 12) The washers are designed to prevent the cracking from reoccurring. Be sure to tighten the screws to specification.
- Thanks to Ann Briedis
On some 2007-2012 Avalanche, Silverado, Suburban, Tahoe, Sierra, Yukon, Yukon Denali, Yukon XL, Yukon Denali XL models equipped with a Trailer Brake Controller (RPO JL1), the cruise control may be inoperative and the Trailer Brake Control Module may set DTC B3894 (Stop Lamp Switch Circuit Plausibility Failure).
If normal diagnostics do not lead to a correction, check the Master Cylinder Pressure Sensor parameter listed in the Trailer Brake Control Module data list. If it is displaying pressure with no brake pedal input, there may be a concern with the master cylinder pressure sensor, wiring/terminals, or Electronic Brake Control Module (EBCM).
TIP: On models with Stabilitrak (RPO JL4), the master cylinder pressure sensor is internal to the Brake Pressure Modulator Valve (BPMV)/EBCM.
- Thanks to Scott Fibranz
On some 2011-2012 Regals, a wobble sensation may be felt in the vehicle or steering when accelerating from a stop through the 1-2 shift and/or there may be a slip/stick condition when the vehicle shifts from 1-2 up to approximately 20 mph (32 km/h). The condition may be easier to duplicate with a passenger in front and/or turning to the right while accelerating.
A new design half shaft is now available to address this condition. Order both the left and right half shafts.
TIP: Once these half shafts have been installed, perform the following break-in procedure:
1. From a stop, accelerate at wide-open-throttle through the 1-2 shift up to 40 mph (64 km/h).
2. Decelerate to a stop.
3. Repeat steps 1 & 2 a total of 20 times.
- Thanks to Christopher Crumb
There may be a lack of power steering assist on some 2013 Regals equipped with electric power steering (RPO NJ1). This condition may be caused by a poor connection at G111.
On vehicles built prior to August 26, 2011, the nut on the ground post may have been loose, which may have allowed paint to enter under the nut and negatively impact the ground connection. (Fig. 13)
Remove the nut and wire from ground post G111 and inspect the base of the ground post and the base of the ground nut. If paint is found, clean the ground post base and replace the M6 nut (GM P/N 11609767). Torque the nut to 8 Nm (71 lb. in.).
- Thanks to Christopher Hightower