Archive for March 2017

New 9T50 9-Speed Automatic Transmission

GM’s all-new Hydra-Matic 9T50 9-speed automatic transmission (RPOs M3E, M3D, M3H) — currently available on the 2017 Malibu, 2017 Cruze Diesel, 2018 Equinox and upcoming 2018 Terrain — is designed to deliver excellent efficiency, performance and refinement. (Fig. 1) By the end of this year, it will be an option on 10 GM models.


Fig. 1


When paired with the Malibu’s 2.0L turbo engine, for example, the transmission helps the sedan deliver an estimated 33 mpg (7.1 L/100km) on the highway — a 3% increase over the 2016 Malibu with the 8-speed automatic transmission.


The transmission consists primarily of a 4-element torque converter, a compound planetary gear set, friction and mechanical clutch assemblies, and a hydraulic pressurization and control system. It employs a wider 7.6:1 overall ratio (compared to the 8-speed transmission) for better acceleration in first gear — 4.69 first gear — and lower engine speeds on the highway — 0.62 top gear —to enhance fuel economy and reduce noise.




Developed to meet the tight packaging requirements of transverse propulsion systems, the 9T50 features an on-axis layout that keeps the planetary gears in line with the engine crankshaft. It also has GM’s first application of a selectable one-way clutch that can hold torque or freewheel, depending on the desired operating mode.


The combination of an on-axis design and a one-way clutch, which eliminates the need for an additional clutch pack, helps reduce overall package dimensions, making the compact 9T50 transmission about the same size as a six-speed transmission.


The transmission uses five planetary gearsets, four stationary clutches and three rotating clutches. (Fig. 2) Gears change from 2nd- to 9th- ratios with precise clutch-to-clutch shifting, with the clutch engaging in one gear at exactly the same time that it’s released from another.


Fig. 2


The hydraulic system primarily consists of a chain driven pump, a control valve body assembly and case. The pump maintains the working pressures needed to stroke the clutch pistons that apply or release the friction components.


The transmission’s single-plate lockup clutch uses an electronically controlled capacity clutch (ECCC) to dampen engine vibrations and ensure smooth operation.


Shift Controls


Commanding all of the shifting events is a 32-bit Transmission Control Module (TCM), which is located outside the transmission. The TCM uses adaptive learning to compensate for new transmission variation and normal wear of the apply components. By adjusting the pressure commands to the various pressure control (PC) solenoids, it maintains the originally calibrated shift timing for consistent shift feel plus increased transmission durability.


TIP: Anytime internal repairs are performed or a revised calibration is installed, the Service Fast Learn Procedure should be performed using GDS2. This helps the transmission learn the clutch fill times initially prior to driving the vehicle. The vehicle should always be driven after the Service Fast Learn Procedure to ensure that the shift quality is acceptable.


To help maintain desired vehicle speed when coasting or braking on a hill, the transmission uses automatic grade braking that can select a lower gear to take advantage of engine braking. The control module receives inputs that monitor brake pedal usage, vehicle acceleration, throttle position, grade and whether a trailer is being towed.


The 9T50 transmission also supports auto engine stop/start operation. A unique accumulator within the transmission allows for refined stop/start transitions. The accumulator stores energy for engine restarts, while the software is calibrated for those smooth restarts.


The 9T50 transmission uses Dexron®-VI fluid. It does not require changing under normal driving conditions.


– Thanks to Mark Kevnick


New Service Information Subsections for 2018 Model Year

For the 2018 model year, there are a number of new subsections that have been added to the Service Information. In addition, several subsections have been moved to different service categories. As a result, if you’re searching for the service procedures on a particular system or component, it might not be where you were used to finding it. The new subsections include additional information and are categorized by the functions of each system.


Current Subsections


Subsections from earlier model years that have been updated or replaced are:

• Horns (Service Category Type: Body Systems) • Object Detection and Pedestrian Protection (Service Category Type: Safety and Security)


New Subsections for 2018


For the 2018 model year, the new subsections are:

• Horns and Pedestrian Alerts (Service Category Type: Body Systems) • Image Display Cameras (Service Category Type: Driver Information and Entertainment) • Parking Assistance Systems (Service Category Type: Safety and Security) • Pedestrian Protection (Service Category Type: Safety and Security) • Driver Monitoring (Service Category Type: Safety and Security) • Driver Assistance Systems (Service Category Type: Safety and Security)


Here’s a summary of the information covered in each of the new subsections.


Horns and Pedestrian Alerts – Systems that alert pedestrians. Located in Service Category Type: Body Systems. (Fig. 3)

• Horn • Pedestrian Alert Sound Control Module


Fig. 3


Image Display Cameras – Systems that provide the driver a visual display. Located in Service Category Type: Driver Information and Entertainment. (Fig. 4)

• Night Vision – Night Vision Control Module • Rear Vision Camera – No Module • Curbview – Video Processing Control Module • Surround Vision (360 Camera) – Video Processing Control Module • Performance Data Recorder (currently in Displays and Gauges) – Vehicle Performance Data Recorder • Full Display Mirror (currently in Mirrors) – No Module • Video Bypass Module – Sometimes used in conjunction with the rearview camera and HMI module


Fig. 4


Parking Assistance Systems – Systems that assist the driver primarily for parking, without providing the driver a visual display. Located in Service Category Type: Safety and Security.

• Parking Assist – Parking Assist Control Module


Pedestrian Protection – Systems that protect Pedestrians in the event of a vehicle-to-pedestrian collision. This is a passive safety system similar to the Supplemental Inflatable Restraint System (SIR). Located in Service Category Type: Safety and Security.

• Inflatable Restraint Sensing and Diagnostic Module


Driver Monitoring – Systems that have a camera facing the driver verifying the driver is focused on the road ahead and participating in safe driving. Located in Service Category Type: Safety and Security.

• Driver Monitoring System Control Module


Driver Assistance Systems – Systems that assist the driver during normal driving without providing the driver a visual display. Located in Service Category Type: Safety and Security. (Fig. 5)

• Lane Departure Warning – Frontview Camera Module • Lane Keep Assist – Frontview Camera Module • Forward Collision Alert – Frontview Camera Module • Side Blind Zone Alert – Rear Short Range Radar(s) • Rear Cross Traffic Alert – Rear Short Range Radar(s) • Integrated Brake Assist, Automatic Collision Preparation, Rear Emergency Braking, and Adaptive Cruise Control – Active Safety Control Module


Fig. 5


– Thanks to Brett Holsworth



Sensor Locations of Hands-Free Power Liftgates

A growing number of GM models now offer an available hands-free power liftgate or trunk, which uses a sensor under the rear bumper (Fig. 6) of the vehicle that, when activated, opens or closes the liftgate or trunk. Depending on the model, the sensor is positioned at different locations under the rear bumper.


Fig. 6


Models that offer the hands-free power liftgate (RPO TC2) include the 2015-2018 Tahoe, Suburban, Yukon, Escalade; 2016-2018 CT6, Envision; 2017-2018 XT5, Acadia; 2018 Enclave, Equinox, Traverse and Terrain.


The liftgate operates when the sensor detects a kicking motion. The hands-free liftgate sensor control module sends a serial data message to the liftgate control module, which activates the liftgate motor in the liftgate power assist actuator. The tail lamps flash when the command has been received.


Sensor Locations


The sensor is located in different positions on the various models that offer the hands-free power liftgate. (Fig. 7)


• Full-size SUVs — Tahoe, Suburban, Yukon and Escalade — and Cadillac CT6: sensor is located under the center of the rear bumper.

XT5 and Acadia: sensor is located behind the driver’s side rear tire on the side of the rear bumper.

• Envision, Equinox, and the upcoming Terrain, Traverse, and Enclave: sensor is located under the left side of the rear bumper, between the left exhaust pipe and the center of the bumper.


Fig 7


Operating the Liftgate


To open or close the power liftgate hands-free, swing your foot in a direct in-and-out motion (your foot should be under the rear bumper for less than one second) in the proximity of the sensor. (Fig. 8) The motion must be within five inches of the sensor. Do not swing your leg in a sweeping or side-to-side motion.


To activate the power liftgate, the Remote Keyless Entry transmitter (key fob) must be within 3 feet (1 meter) of the liftgate.


Fig. 8


The hands-free feature will not work while the liftgate is moving. Use one of the liftgate switches to stop the liftgate while in motion.


The hands-free feature also may be temporarily disabled under some conditions. If the liftgate does not respond to the kicking motion, open or close the liftgate by another method or start the vehicle. The feature will be re-enabled.


Projected Logo


Some 2018 models feature a vehicle logo that is projected onto the ground under the rear bumper sensor that indicates where the kicking motion should take place. The logo is projected when the key fob is detected within 6 feet (2 meters) of the liftgate.


Under normal conditions, the logo will be projected for one minute. If the logo is not projected, check for the following operating conditions:

The projected logo is only available for the currently used key fob after it has been out of range for at least 20 seconds.

If a key fob is again detected within approximately 6 feet (2 meters) of the liftgate, or another hands-free operation has been detected, the one-minute timer is reset. If it is reset five times in 10 minutes, the logo will not turn back on for one hour. This provides the battery with a “cool-down period” to preserve its charge.

If the vehicle remains parked for an extended period of time with no key fob use or Keyless Access operation, the projected vehicle logo will be disabled. The projected logo will be re-enabled when any key fob button is pressed, any vehicle door is opened and closed, or the liftgate is closed when all doors are opened.

The projected logo will not work for a single key fob when a key fob has been left within approximately 15 feet (5 meters) of the liftgate for several minutes, has been left inside the vehicle and all vehicle doors are closed, or has approached the area outside of the liftgate several times in a short period of time.


Users can customize hands-free operation. The kick function can be turned off, only open the liftgate, or open and close the liftgate. To change the kick function:

1. Select the Hands-free Liftgate Control menu on the infotainment screen under Settings > Vehicle > Comfort and Convenience.

2. Select Off, On-Open Only, or On-Open and Close.


Selecting Off will disable hands-free control of the liftgate and keep the logo lamp off.


– Thanks to Gary McAdam



Fuel Line Pulsation Sound

A rattle or ticking sound may be heard coming from the back of the left valve cover on some 2014-2017 Corvette, Silverado, Sierra; 2015-2017 Tahoe, Suburban, Yukon, Escalade; 2016-2017 CTS-V, and Camaro models equipped with the following engines: 6.2L (RPO LT4, LT1, L86); 5.3L (RPO L83); or 4.3L (RPO LV3) It may sound similar to a lifter ticking and may be louder inside the vehicle.


Listen to the fuel line connection at the left side of the engine. The fuel feed line between the high pressure fuel pump and chassis fuel line may be allowing high pressure pulsation back to the low side of the fuel system. If the sound is heard, the line will need to be replaced. On some trucks and SUVs, a vibration also may be observed in the fuel line at the fuel tank.


There are two different types of fuel lines that contain a check valve. The lines vary by model. Only one line should be used on Corvette, truck and SUV models. (Fig. 9) The line connects the chassis fuel line to the high pressure fuel pump. (Fig. 10)


Fig. 9


Fig. 10


– Thanks to David Rutkowski

Missing Connector Seals

Some 2015-2017 Silverado, Tahoe, Suburban, Colorado, Sierra, Yukon, Canyon, and Escalade models equipped with 4WD (RPOs NQF, NQH, NQ6, NPO, NG7) may have an intermittent Service 4 Wheel Drive message displayed on the Driver Information Center (DIC). There may be several wiring terminal issues caused by missing seals.


When diagnosing intermittent Transfer Case Control Module DTCs related to signal or circuit integrity, including DTCs C0321, C0392, C0396, C0398, C0306, C039E, and C038D, inspect the associated connectors to ensure that the seals are properly installed (Fig. 11, #2) in the connectors. Missing seals (Fig. 11, #1) allow moisture inside the connector and will cause repeat conditions or other intermittent conditions.


Fig. 11


Some connectors are serviced as a connector, while some have terminated leads and others are available as a harness only. If there is corrosion in the connector and it has to be replaced, the mating side of the connector should also be replaced regardless if it is another connector or an electrical component. For example, if the connector at the transfer case actuator is replaced due to a missing seal and corrosion is present, the transfer case actuator should also be replaced.


– Thanks to Steve Schipansky

Supercharger Idler Pulley Sounds

A scraping or moaning sound may be heard from the supercharger idler pulley on some 2017 CTS-V, Corvette; and 2017-2018 Camaro models equipped with the supercharged 6.2L V8 engine (RPO LT4). The sound will be most noticeable when the engine is idling.


This condition has the following VIN breakpoints:



If the pulley sound is found, replace the idler pulley assembly. (Fig. 12)

Fig. 12


– Thanks to Richard Renshaw


Updated June 1, 2017

Techline Data Service Update

TDS available in TIS2Web for all dealerships

TIS2Web and the Service Programming System (SPS) put vehicle software calibration files within easy reach during programming. They just need to be downloaded from the internet. But what if the files were already downloaded and waiting in your dealership when needed? The Techline Data Service (TDS) does just that, making programming faster and easier, especially for longer infotainment SPS events.


TIP: Techline Data Service (TDS) distribution was completed in June 2016 and TDS has been activated for all GM dealerships. A TDS tab can be found in TIS2Web. (Fig. 1)


Fig. 1


TDS is an enhancement to the way larger vehicle software calibration files are delivered and managed through TIS2Web. Previously, large files, such as infotainment software, were distributed to dealerships via DVD and USB drives, leaving them susceptible to being damaged or misplaced. With TDS, files are simply downloaded once and are available to all through the dealership’s network.


Automatic Downloads


Once TDS is installed and configured in the dealership, files are sent automatically to a dedicated computer during hours designated by the dealership, including during non-business hours or overnight. By having only one computer downloading the large calibration files, it eliminates the need for each PC in the service department to download large files throughout the day and exhaust internet bandwidth. Other Techline PCs in the shop can quickly pull the files from the dedicated computer through the shop’s network when needed. There’s no waiting.


Looking forward, as the size of programming files continue to increase, inevitably so will the wait times to download them through an internet connection during busy business hours. That means valuable repair time could be saved during every programming event if the large files are ready and waiting in the dealership in advance of needing them.


Techline cache DVDs and infotainment DVDs Discontinued


TDS is currently optional for GM dealerships, but it has been designed to take the place of the Techline cache DVDs and infotainment DVDs, which have been discontinued.


SPS calibrations are available over the internet through TIS2Web during the SPS programming event, but the time required for this method depends on your local download speed and network conditions.


Required computer equipment


The PC minimum requirements for TDS are:

• Windows 7 Professional • A minimum 500 GB free hard drive space and 4 GB RAM. • The PC should be dedicated and powered on at all times to receive calibration files continuously. • The PC should be hard wired to the network (wireless is not recommended). • The PC must be a desktop (recommended) or laptop computer. Servers do not qualify.


In the U.S., visit to purchase a TDS certified computer for your dealership. Review the GM Dealership Infrastructure Guidelines before purchasing a new computer.


Installation Instructions


All GM dealerships currently have TDS activated through TIS2Web. A TDS tab is on the TIS2Web home screen. Following are the quick set-up instructions for installing TDS on one dedicated computer (“server”) and on the Techline PCs in the shop that will be pulling files from the dedicated computer.


Server Installation:

1. Designate one computer in the shop to be the “server” that will download files for all other Techline PCs to use. 2. On the dedicated computer, open the TDS tab in TIS2Web and click “Start TDS Installation.” 3. Use all default settings during installation. 4. While TDS is loading, if a Windows Security Alert appears, check all boxes and allow access. 5. Once installation is complete, a Techline Cache (TLC) Administration window will appear. Write down the value of the TDS Server (Share) option. This will be used during the PC client installation. 6. Close the Techline Cache (TLC) Administration window. Set-up is complete.


PC Client Installation:

1. Start SPS from TIS2Web. 2. While SPS is loading, if a Windows Security Alert appears, check all boxes and allow access. 3. Once SPS is launched, close the SPS window. 4. Click the GM Techline Cache icon, located in the system tray or near the clock on the PC, to open the Techline Cache Administration application. 5. Once the Techline Cache Administration window has opened, verify the TDS Server (Share) value is the same as noted on the “server” computer. 6. If the PC client and “server” computer have the same value, TDS installation is complete. 7. Close the Techline Cache (TLC) Administration window.


For complete installation procedures and operating information, refer to the Techline Data Service User Guide. The guide is available on TIS2Web by clicking the Help icon (question mark) and selecting the User Manual menu of the left side of the Help screen.


– Thanks to Chris Henley



GDS2 Offline Mode in Latest Software Update

GDS2 software updated version 17 was recently released. This update features a major application change that allows GDS2 to operate in Offline mode when an internet connection is not available.


If the PC does not have any network connection, GDS2 will now run in Offline mode, even if the PC is connected to a wireless hub. When no network connection is detected, a message will flash for five seconds stating that GDS2 is in Offline mode. (Fig. 2)


Fig. 2


The current network connection status, indicated by an icon, is displayed in the lower right corner of the screen. (Fig. 3)

Possible status connections are:


Fig. 3

Ready to connect GDS2 is in Online mode and ready to connect to TIS2Web.


Problem connecting GDS2 is in Online mode but has a problem connecting to TIS2Web.


Unknown GDS2 connection mode is unknown. This status is usually seen at application startup and is only briefly displayed.


Working GDS2 is busy connecting to TIS2Web.


Offline mode This new icon indicates GDS2 is running in Offline mode.


If RPO questions have not been answered before going offline, they need to be answered manually. If RPO questions are already answered, they will be applied automatically. The connection icon would remain at “Ready to connect” state until the next connection check.


When a network connection is restored, GDS2 will automatically switch to Online mode at the next connection test.


TIP: Once a month, the GDS2 diagnostic package also is updated. It contains updated information on individual vehicle platforms. These updates are available in GDS2 by clicking on the “Update” button or by clicking on “Manage Diagnostic Packages.”


Look for the GDS 2 update when logging into TIS2Web and launching GDS2.


– Thanks to Chris Henley

2017 Service Manager Satisfaction Survey Ends May 5

The 2017 Service Manager Satisfaction Survey is now available to service managers of all GM dealerships. The deadline for completing the survey is May 5.


GM and other automotive manufacturers co‐sponsor the industry study of service managers across the United States. The results of the survey help to determine industry trends and satisfaction levels with the services and support provided by all manufacturers.


The survey should take around 30 minutes to complete. Your feedback is extremely important and will be shared within GM in order to help develop the support programs that will deliver an exceptional ownership experience for all GM customers.


In response to input on the 2016 survey, improvements were made by GM in several areas affecting dealership service departments:

• Customer Assistance Support ﴾CAC/Roadside/Courtesy Transportation﴿ • Rewards/Recognition • Technical Support ﴾PQC, Techline, FSE, TAC﴿ • Service Information • Service Retention • Service Marketing Support


One item put in place based on service manager feedback was a remote access button that was added to TIS allowing the Techline Customer Support Center (TCSC) to take control of a dealership PC when troubleshooting. With remote access, TCSC is able to reduce the amount of time it takes to provide a resolution to a technical issue.


Another example is the new Loan Tool Program (LTP) that augments the U.S. Essential Tool Program. The LTP provides a cost-effective alternative to required purchases of high cost and/or infrequently used special tools. Communication with GM dealerships to build awareness of new essential tools also has been enhanced with announcement flyers included in every essential tool shipment and on the GM Tools website. The announcements include the part number, a description of the part, vehicle applications, and the reason for the tool.


Take the 2017 Survey


To access the 2017 survey, visit (Fig. 4)


When prompted, enter:

• Manufacturer/Brand: GM • Dealer Code: your 6‐digit BAC code


Fig. 4


If you are interrupted or have to leave the survey before completing it, it automatically tracks your progress so you can return at any time and pick up where you left off.


If you would like your ratings to be anonymous you may indicate this at the beginning of the survey. Your written comments will not be anonymous so that you can be contacted if needed to clarify or discuss your responses. Your comments are extremely important. They ensure that GM clearly understands your concerns.


Answer all the questions you can; seek assistance of others in your dealership if necessary. If a question does not apply specifically to your operations, please leave the question blank.


If you have any questions, contact George Kalso at Please include your dealer code and contact information.


– Thanks to George Kalso

Front View Camera Calibration

When replacing a front view camera module (Fig. 5) on 2012-2018 GM models equipped with a front view camera, it’s necessary to reprogram the module as well as perform the calibration process for the front view camera system. The calibration process will not start automatically using the Service Programming System (SPS) and must be initiated with GDS2.


Fig. 5


TIP: Refer to the appropriate Service Information to determine if the front view camera module requires programming and/or calibration.


The front view camera detects visual cues such as lane markings. On a system such as Lane Keep Assist, the front view camera module receives an input from the Lane Keep Assist switch and controls the Lane Keep Assist switch indicator output. The front view camera module also communicates via serial data with the instrument cluster, radio, and memory seat module to request visual, and audible or haptic alerts.


Calibration Conditions


Follow the calibration procedure listed in the appropriate Service Information. The calibration process should be completed within 3–5 minutes when the proper driving conditions are met. If the conditions are not met, the front view camera module will continuously run the service point calibration until the calibration process is successfully completed.


To calibrate the front view camera module, the following conditions must be met:

• Clean windshield • Avoid lane changes • Maintain vehicle speed between 35–56 mph (56–90 km/h) • Ensure the road contains visible references (well defined lane markings, curbs, etc.). • Camera is properly installed. Verify it is snapped into tabs and secure.


No Calibration


If the front view camera module calibration is not completed successfully, check the following items:


1. Review the Manufacturer’s Enable Counter (MEC) parameter in the Identification Information data list. It must equal zero or the learn procedure will not function. The MEC is the third parameter from the top of the list. If it is not zero after programming, contact the Techline Customer Support Center (TCSC).


2. Review the parameter Frontview Camera Learn Mode Status in the GDS2 FCM Data Display to confirm the Learn State value. • If this parameter shows Not Learned, press the Learn button under Frontview Camera Learn in Config/Reset Functions. • If this parameter shows Learn Enabled, do not press the Learn button again. The Learn function is already enabled and the vehicle just needs to be driven. • If this parameter shows Learned, the system is learned and operational.


3. Do not press the Learn button in GDS2 more than once. If the Learn selection button has been pressed, a second button press will cause the FCM Learn function to fail. (Fig. 6) Confirm state of learn by looking at the Frontview Camera Learn Mode Status parameter.


Fig. 6


– Thanks to Bret Raupp 

Duramax Diesel Engine Coolant Leak

2017 Silverado and Sierra models equipped with the 6.6L Duramax diesel engine (RPO L5P) may display a Driver Information Center low coolant message or may show coolant consumption or a coolant leak. These conditions may be due to cooling system leaks or an improper coolant fill procedure.


When diagnosing these conditions, be sure to complete the coolant system leak checks in the appropriate Service Information to verify there are no external leaks. It may take a few engine temperature cycles, from operating temperature to cold, for the coolant level to show a lower than normal level.


TIP: Do not pressure test the coolant system.


Coolant Loss


Check for coolant leaks at the welded flange on the Exhaust Gas Recirculation (EGR) coolant return pipe (Fig. 7) and coolant feed pipe. (Fig. 8)


Fig. 7


Fig. 8


In addition, check the O-ring seal on the EGR coolant feed pipe for a coolant leak. The O-ring may be pinched or rolled. (Fig. 9) It may be necessary to remove the front accessory drive bracket and alternator.


Fig. 9


Coolant also may leak from the coolant hoses at the Emission Reduction Fluid Injector (DEF injector). (Fig. 10)


Fig. 10


Radiator Surge Tank


The radiator surge tank uses two different radiator surge tank caps. The radiator surge tank cap that vents pressure in the event of excessive cooling system pressure is located on the lower outboard side of the radiator surge tank. The radiator surge tank cap that is located on top of the radiator surge tank is where the cooling system is filled. It has left hand threads; turn the cap clockwise to remove the cap and counterclockwise to install the cap. If the cap is turned in the wrong direction when installing or removing it, there may damage to the cap and/or the surge tank.


– Thanks to John Stempnik

Ticking Sounds on Active Fuel Management Cylinders

A ticking or knocking sound may be heard on some 2016-2017 ATS, CT6, CTS, Camaro; 2017 LaCrosse, XT5, Colorado, Canyon and Acadia models equipped with the 3.6L engine (RPO LGX). The 3.6L engine uses Active Fuel Management (AFM) to conserve fuel. The ticking or knocking sound may be heard coming from the AFM cylinders. DTCs P0300 (Engine Misfire Detected), P0302 (Cylinder 2 Misfire Detected) or P0305 (Cylinder 5 Misfire Detected) may be set.


The ticking or knocking sound may be heard all the time, only under load, or intermittently. The sound may be caused by spongy stationary hydraulic lash adjusters (SHLA) (lifters) or a damaged switching roller finger followers (SRFF).


TIP: Prior to disassembly of any components, record a sound file or video with sound of the engine running. The file may be needed when contacting the Technical Assistance Center (TAC) or may be requested by GM Engineering.


Refer to #PIP5486 for diagnostic and repair instructions. The diagnostic steps must be performed in order.


Diagnosis includes verifying the injectors are not leaking and causing a noise due to excessive fuel in one cylinder as well as inspecting for excessive carbon on the intake valve stems and the top of the valve.


If the sound is still evident after these steps, test for soft or spongy stationary hydraulic lash adjusters (SHLA). (Fig. 11)


Fig. 11


It also may be necessary to inspect the switching roller finger followers (SRFF) for any damage, such as a stuck locking pin or fractured torsion spring. (Fig. 12) If any one of the SRFFs are damaged, replace all four on the affected cylinder.


Fig. 12


– Thanks to Aron Wilson

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