Archive for October 2014

New Data Bus Diagnostic Tool

GM has released new diagnostic software to help technicians identify a starting point in diagnosing faults in a CAN bus (GM also calls this a LAN) by looking at how connectors and wiring are working or not working.


The Data Bus Diagnostic Tool is an application that uses existing MDI functionality. You will use your MDI, a Techline terminal, and an active TIS license.


To download the software, click the GDS 2 icon on the TIS2Web home page. (Fig. 1) A prompt to install the software will appear. The software will be available through TIS2Web as part of a rollout that began October 13, 2014 and continues until October 27, 2014. If a prompt does not appear when clicking the GDS 2 icon, the software has not been activated for your dealership, but will be available shortly during the rollout.


F01 bus gds2

Fig 1


Diagnostic Aids


If there’s a high speed communication issue and 20 U codes set in every module, those DTCs aren’t very useful in narrowing down the concern. The new Data Bus Diagnostic Tool software will show counts of each module and how often it’s NOT communicating. This very quickly identifies the problem module, and provides a quick point of diagnosis for checking the connectors, terminals and wiring for that module. It’s proven extremely useful in field testing for these issues.


Localizing the Fault


The application actively queries all possible diagnostic addresses to see what modules are on the bus. Modules that respond are on the ‘good’ part of the bus. Modules that don’t respond are on the ‘bad’ part of the bus.


The application doesn’t know what modules a vehicle is equipped with, so it can’t report which modules are missing. Compare the list of modules displayed in the application against that vehicle’s schematics in the appropriate Service Information.


TIP: Under a hard short, no communication is possible, so no modules will be listed.


Determine Physical Layer Status


CAN buses have characteristic voltages under different fault conditions. By monitoring bus voltage, it’s possible to identify whether or not the bus is physically OK. It’s also possible to identify the type of fault that’s present (CAN LO/HI open, short, ground offsets, etc) by monitoring bus voltage.


TIP: No message data is taken into consideration.


Three-In-One Application


The Data Bus Diagnostic Tool is actually three sub-applications in one, including Detected State (Fig. 2, A), Measured Voltage (Fig 2, B), and Message Monitor functions. (Fig. C) Each one has its own tab on the application’s graphic interface.


F02 bus tabs

Fig 2


Detected State – Identifies which control modules are responding to diagnostic requests, and identifies the physical state of the vehicle bus being diagnosed (i.e., open, short, ground offset, etc). (Fig. 3)


In performing these functions, this tab does three things:


1. It provides a diagnostic starting point. All possible ECUs are sent simultaneous requests at a rate of 250 ms. The application tracks and displays the longest time it takes for each ECU to respond to a diagnostic request to help with intermittent faults.


2. It tries to identify what’s going on with the wires that make up the bus (i.e., OK, CAN LO/HI open, CAN LO/HI shorted to ground, ground offsets, enable line open/blown fuse/power faults, etc.).


3. It provides audible feedback. You can set the application to beep continuously when a fault is detected or when the bus appears electrically OK.


F03 bus detected

Fig 3


This is a list of states that can be detected.

• OK

• Single wire opens (ie CAN LO Open, CAN HI Open)

• Double opens

• Single wire shorts to power/ground

• Single wire open/short (i.e., the wire is broken and the far side is shorted)

• CAN LO shorted to CAN HI

• Ground offsets (i.e., bad ECU grounds)

• Power faults (i.e., open supply, blown fuse, broken enable line, etc)


Using the Detected State, if a bus has a break point in communication, some modules on the “good” side of the faulted bus will respond very intermittently. When diagnosing intermittent faults, pay attention to the ECU with the longest response time and use the electrical schematic.


Place a check mark on the schematic next to the modules noted on the Detected State test. Modules without a check mark are the modules that did not communicate during the Detected State procedure.


Measured Voltage — Provides a low speed voltage trace of the selected bus, CAN LO and CAN HI. (Fig. 4) Due to current MDI limitations, it refreshes at about 1 ms, so it’s not as fast as an oscilloscope. It also won’t let you see the individual bits in a CAN frame (CAN frames take about 0.25 ms to transmit). It is, however, very visually obvious when a fault is introduced or removed.


F04 bus voltage

Fig 4


Message Monitor — Passively monitors bus activity to help diagnose battery drain problems. (Fig. 5)


The biggest difference between Message Monitor and Detected State is that it this passively monitors the bus, while Detected State actively queries the bus. Actively querying ECUs will make some of them stay awake. Obviously, keeping ECUs awake would be a bad thing if you’re trying to diagnose a power moding fault.


F05 bus monitor

Fig 5


This tab will tell you which ECUs have communicated in the past 1.5 seconds, how long it’s been since ECU last communicated (if more than 1.5 seconds have elapsed), and how many times the ECU was the first ECU talking on the bus (the bus is considered ‘asleep’ after 30 seconds of idle time).


TIP: This tab works on Single Wire CAN only.


Audible Feedback


The application will beep when either a fault is detected or when the bus appears electrically OK. This is user configurable by selecting the Settings function. (Fig. 6) Different beep strategies can be used in different scenarios.


F06 bus beep

Fig 6


In the case of a vehicle with a suspected intermittent bus fault, you might want to make the application beep on faults so that it will beep when the fault is detected.


In the case of a vehicle with a continually faulted bus, you might want to make the application beep when the detected fault goes away.


The application reacts to bus changes quickly (approximately 100 ms). Wiggle connectors and listen for a beep.


TIP: Be sure to unmute your PC speakers and the application.


Tracking Intermittent Faults


The application tracks the longest time it takes for each control module to respond to a request. Control modules which take longer to respond than their peers were/are likely on the faulted side of the bus.


If the application is started on a faulted bus and a module responds mid-way through the test, it will appear with a non-zero time value in this field.


TIP: This number will not reset unless the reset (eraser) button is clicked or the bus being tested is changed.


More Information


U.S. dealerships: For more information about the new software, check out the TechTube video on the GM Center of Learning website at The software also was featured in the October 2014 Emerging Issues seminar.


Canadian dealerships: The new software will be featured in the November 2014 TAC Talk.


In addition, a user guide for the software is available in the Service Information.


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


– Thanks to Chris Henley and David Gumpert

GM Techline Announces No Windows® 8 Support

After a detailed study regarding support of Windows® 8 and 8.1 Professional, GM Customer Care and Aftersales has determined that Windows 8 does not offer any new features necessary to diagnose and repair vehicles and that Techline applications will not adopt the Windows 8 operating system as part of the GM Dealership Infrastructure Guidelines.


Compared to the Windows 7 Professional operating system, which is designed for the business community, Windows 8 targets consumer users.


Recommended Specifications


Before purchasing a computer for use in the dealership, the GM Dealership Infrastructure Guidelines should be reviewed to ensure that the computer meets or exceeds the minimum specifications. The GM Dealership Infrastructure Guidelines – Service Department can be accessed at (In Canada, the IT guidelines are in the Service Library under Tools, Processes and Equipment on Global Connect.)


Major PC manufacturers offer several laptop computers with Windows 7 Professional, referred to as business-grade offerings.


The GM guidelines specify that the computer must include business-grade hardware that meets or exceeds the minimum specification with Intel Processors and runs the Windows 7 Professional 32 bit or 64 bit operating system.

Screen Shot 2014-10-22 at 11.43.08 AM

GM Dealer Equipment includes a variety of laptops, tablets and desktop computers that meet GM guidelines. Go to and click the Techline IT Solutions tab for more information. In Canada, go to


Computers purchased preinstalled with Windows 8.1 Pro software may include downgrade rights to Windows 7 Professional. Contact your PC manufacturer or refer to Microsoft’s website for further details regarding eligibility and available options.


Internet Bandwidth


GM recommends that dealerships maintain a minimum network bandwidth. Inefficient bandwidth may result in unreliable or slow performance and may negatively affect the speed and functionality of GM applications

Screen Shot 2014-10-22 at 11.43.19 AM

Any questions about computer specifications in the U.S. and Canada can be directed to the Techline Customer Support Center (TCSC) at 1-800-828-6860 (English) or 1-800-503-322 (French).


– Thanks to Lisa Scott

Techline User Guides Available in the Service Information

Technicians looking for more information about Techline applications can find a variety of valuable information in the GM Service Information.


The following User Guides are available under the Select and View a User Guide link (Fig. 7) on the Service Information home page:

• Techline Information System (TIS)

• Global Diagnostic System 2 (GDS 2)

• Global Service Information

• Multiple Diagnostic Interface (MDI)

• Data Bus Diagnostic Tool.

 F07 user guide home

Fig 7


As part of the Service Information system, model years are attached to the user guides.


Each guide provides an overview of the system as well as important reference information about the different features of the system and how to best use them. This includes information such as identifying the functions of the buttons and links on each application, such as the GDS 2 main application screen. (Fig. 8) Other information covers a variety of programming and diagnostic features of the applications.


F08 user guide gds2

Fig 8


The TIS user guide covers all of the applications of the system along with how to navigate within the TIS software and how to use other tools that interface with the system. For example, the user guides present detailed instructions for programming using a USB flash drive (memory stick)


If you have questions about any of the TIS applications, check out the user guides in the Service Information. For more information, the Techline Customer Support Center (TCSC) is always available. Contact the TCSC at 1-800-828-6860 (English) or 1-800-503-322 (French).


– Thanks to Lisa Scott


Take the 2014 Service Advisor and Technician Satisfaction Survey

The 2014 Service Advisor and Service Technician Satisfaction Survey is taking place now for U.S. dealerships and you’re encouraged to voice your opinion.


GM and other automotive manufacturers co-sponsor this annual survey of service technicians and service advisors from across the country. The purpose of the survey is to collect feedback on dealership service trends, satisfaction levels, and dealership operational issues regarding the level of support from GM and the dealership.


Service Technicians


To access the service technician survey, go to (Fig. 9)


F09 survey screen

Fig 9


Service Advisors


To access the service advisor survey, go to


To complete the survey, you will need your 6-digit Dealer Code/BAC Code. The survey should take approximately 15 minutes to complete.


All survey responses are strictly confidential and will not be shared with your dealership.


The 2014 survey will be available until November 7, 2014.


Your feedback is very important. Please take this opportunity to provide your comments and suggestions about your experiences.


– Thanks to George Kalso

Engine Oil Dipstick Indicates an Overfill

On some 2015 Escalade models and 2014-2015 Silverado 1500, Suburban, Tahoe, Sierra 1500, and Yukon models equipped with the 5.3L or 6.2L engine (RPOs L83, L86), the engine oil dipstick may indicate an overfill when performing a Pre-Delivery Inspection (PDI) or after an oil and filter change.


Typically, this condition will show that the engine oil dipstick indicates an overfill of 1/2 quart of oil. There is no need to drain the oil at this time. This condition will not damage the engine or affect operation.


When it is time for an oil change, fill the engine with the recommended amount of engine oil as specified in the appropriate Service Information, which has been updated with the engine oil (with filter) fill specification of 8 quarts (7.5 liters) for the 5.3L and 6.2L engines. The correct Full mark on the dipstick is the upper dimple and the Add mark is the lowest bottom dimple on the dipstick. (Fig. 10)


F10 oil dipstick image

Fig 10


– Thanks to Richard Renshaw


Vibration in AFM V4 Mode

A vibration may be felt between 1200–1400 RPM when the engine is in Active Fuel Management (AFM) V4 mode on some 2014-2015 Silverado and Sierra trucks equipped with the 4.3L V6 engine (RPO LV3). A drone or resonance may also accompany this vibration. The vibration may occur at different vehicle speeds but the engine speed will be in the 1200–1400 RPM range. The vibration does not occur in V6 mode.


Evaluate the vehicle under the conditions that duplicate the condition. Once the condition is duplicated, use a vibration analysis tool, such as the J 38792-A Electronic Vibration Analyzer 2 (EVA) or CH 51450-NVH Oscilloscope Diagnostic Kit (w/NVH) to measure the frequency of the vibration.


If the measured vibration is not 23 Hertz (HZ), first order engine, use normal vibration diagnostics to isolate the source of the vibration.


If the measured vibration is 23 Hertz (HZ), first order engine, follow the following three-way catalytic converter settling procedure, which includes the following components: (Fig. 11)

1. Left exhaust manifold nuts

2. Seal

3. Right exhaust manifold nuts

4. Seal

5. Exhaust muffler clamp and nut

6. Catalytic converter


F11 cat image

Fig 11


TIP: Do not replace the three-way catalytic converter assembly unless it is physically damaged.


• Loosen the six nuts that fasten the three-way catalytic converter assembly to the exhaust manifolds.

• Remove and replace the exhaust muffler clamp that joins the three-way catalytic converter assembly to the pipe of the muffler assembly. This is a one-time use Norma clamp that must be replaced.

• Reinstall the three-way catalytic converter assembly following the specific tightening sequence and fastener torque specifications found in the appropriate Service Information.


– Thanks to David Rutkowski


Premature Catalytic Converter Failure

If the catalytic converter has failed or DTC P0420 (Catalyst System Low Efficiency) or P0430 (Catalyst System Low Efficiency Bank 2) is set on some 2015 and prior GM cars and gasoline-powered mid-size trucks, light-duty trucks and heavy-duty trucks, inspect for a poor crimp at circuit terminal on the engine bank with the condition.


Inspect the ground for possible corrosion or damage at the ground terminal ring, fasteners and grounding surfaces. (Fig. 12, 13)  If no corrosion or damage is found, tighten the ground bolt to the proper torque specification. (Fig. 14)


F12 3992547 ground pci 1

Fig 12


F13 3992548 ground pic 2

Fig 13


F14 3998036 ground 3

Fig 14


– Thanks to Richard Renshaw

A/C Refrigerant Leak

The air conditioning may be warm and the A/C refrigerant level may be very low/empty on some 2015 Escalade models; 2014-2015 Silverado 1500 and Sierra 1500; 2015 Suburban, Tahoe, and Yukon models. For the 2015 models listed, this only applies to early built 2015 models that have a muffler in the compressor to condenser line.


Here’s an example of the line: (Fig. 15)

1. Compressor to condenser line without a muffler

2. Compress to condenser line with a muffler


F15 3992036

Fig 15


After performing normal diagnostics, if the source of the refrigerant leak is either not found, or it is found at/near the rear of the compressor, check for a small crack in the compressor to condenser line. The line may have a small crack or pin hole located at the inside radius of the first bend near the compressor. (FIG. 16)


F16 3980076

Fig 16


If the A/C line cracks, it may spray oil and refrigerant onto the A/C compressor, making the source of the leak very hard to identify.


To repair this condition and prevent it from reoccurring, replace the compressor to condenser line and install the line bracket as shown. (Fig. 17) After completing repairs, recharge the refrigerant system and perform a leak test to verify proper operation.


F17 3991846

Fig 17


Refer to #PIT5331 for additional information and part numbers.


– Thanks to Jim Will

Rainsense Wipers Sensitivity Adjustment

Drizzling rain on a windshield can be a nuisance to drivers, causing frequent adjustments to the intermittent wiper settings in order to clear the windshield of varying amounts of water. The answer to this dilemma is the Rainsense™ wiper system available on some GM models, including all 2015 Cadillac models, full-size SUVs (Tahoe, Suburban, Yukon models, Escalade models), Chevy SS, and others.


With the Rainsense system, a sensor near the top center of the windshield (Fig. 1) detects the amount of water on the windshield and controls the frequency of the windshield wiper.


2014 Buick Encore with Rainsense

Fig 1


TIP: On some 2014-2015 models, the Rainsense wiper system can be turned on or off in the Vehicle Personalization settings. On the infotainment system, go to the Settings > Vehicle > Comfort and Convenience menu and select Rain Sense Wipers to enable/disable the Rainsense wipers feature.


Click to view an overview of the Rainsense system on the Buick Encore. (Fig. 2)

F02 rainsense video

Fig 2


Sensitivity Control


On vehicles without the Rainsense system, moving the windshield wiper lever or wiper band to the Intermittent position (INT) activates the timed delay of the wipers. The wipers cycle automatically after a short delay. Rotating the INT band up (more frequent wipes) or down (less frequent wipes) on the wiper lever changes the timed delay.


On vehicles with the Rainsense system, moving the windshield wiper lever or wiper band to the Intermittent position (INT) activates the Rainsense feature. With the system on, the INT band works as a sensitivity setting. (Fig. 3) The wipers will activate automatically based on the amount of water on the windshield. Rotating the INT band on the wiper lever changes the sensitivity of the moisture sensor. If the sensitivity setting is increased, the wipers will cycle when there is less water on the windshield (more frequently). If the sensitivity setting is decreased, the wipers will cycle when there is more water on the windshield (less frequently). Move the wiper lever or wiper band out of the INT position to turn off the Rainsense feature.


F03 wipers int

Fig 3


The 2015 full-size SUVs have an AUTO button on the wiper lever that turns the Rainsense system on or off. (Fig. 4) Use the INT band on the wiper lever to adjust the sensitivity setting. The band must be in one of the sensitivity settings for the Rainsense system to operate; otherwise, a Driver Information Center (DIC) message will be displayed requesting INT to be selected for the Rainsense wipers.


F04 wipers auto

Fig 4


In these vehicles, if the AUTO button is pressed with the wiper control in the Off, Low or High position, a DIC message will display indicating that the wiper control needs to be in the INT position.


A DIC message also will display each time the system is turned on/off.


The Rainsense system will remain on after an ignition cycle if it was on when the ignition was turned off.


If the AUTO button is pressed to turn off the Rainsense system, the wipers operate as timed intermittent wipers and can be adjusted for a shorter or longer timed delay.


Wiper Arm Assembly Protection


It’s recommended to turn off the Rainsense wipers when using an automatic car wash. If the system is on, the transmission is in N (Neutral) and the vehicle speed is very slow, the wipers will automatically stop at the base of the windshield in order to protect the wiper arms. The wipers will return to normal operation when the transmission is no longer in Neutral or the vehicle speed has increased.


Moisture Sensor


The Body Control Module (BCM) controls the wiper motor based on an input from the wiper switch, and when wiper operation is requested, the BCM sends serial data messages to the windshield wiper motor module. (Fig. 5)


F05 sensor system

Fig 5


The BCM communicates with the moisture sensor via LIN serial data communication messages. When the windshield wiper control is in the INT position, the BCM provides the moisture sensor with the current sensitivity setting. The sensor monitors the water on the windshield and the sensitivity setting, and requests the BCM to perform windshield wipes as it determines they are required.


The wiper blade wipes across the sensor, clearing the water. Worn or dirty wiper blades, or blades that are not the correct size, may not properly clear water from the windshield in front of the sensor. Glass treatments also can cause water to sheet off the windshield, making it difficult for the sensor to properly determine the amount of moisture.


On vehicles with the Global A electrical architecture, if a fault occurs between the moisture sensor and BCM while Intermittent, Low, or High speed wipes are operating, the BCM will continue to provide Intermittent, Low, or High speed wipes, respectively. This will be performed until the ignition or the wiper control is turned off.


On earlier common architecture vehicles, the Intermittent positions of the windshield wiper switch are used to operate the windshield wiper in timed intermittent delay intervals.


A DTC will set if communication between the BCM and the moisture sensor is interrupted. Follow the appropriate Service Information for any set DTCs.


If replacement of the moisture sensor (Fig. 6) is necessary, do not touch the sensor on the side that attaches to the windshield. Any contamination, such as a fingerprint, on the sensor will affect how it reads the moisture on the windshield.


F06 moisture sensor r

Fig 6


TIP: Do not remove the protective cover on a new sensor until it is being installed. Use care to avoid getting any dirt or fingerprints on the windshield side of the sensor during installation.


When installing the moisture sensor, latch the mounting tab on one side and then the other. This will prevent a large amount of air getting trapped. Ensure that both the sensor’s mounting tabs are properly latched. If the tabs are not latched, it will lead to degraded moisture sensor performance.


– Thanks to Jon Nowak and Mark Willey

Talk with Techs on the SI Forum

Looking for a discussion with other technicians about diagnostic and repair information, service polls, and GM service applications? Check out the Service Information (SI) forum at A one-time registration is required.


The SI forum is a website designed by GM to promote communication among the GM technician community. Repair information on all GM brands, polls on a variety of GM service initiatives, and common questions about service applications such as GDS 2, Techline systems and others are just a few things that can be found on the forum. (Fig. 7)


There are various subject matter experts that monitor the forum and assist with concerns and unanswered questions.


F07 forum 1

Fig 7


Wide Range of Topics


The forum is organized in categories that range from specific diagnostic and repair information to general comments on daily life in the service bay. The topics focus on diagnostic and repair information for individual vehicle lines; general technical information covering training, OnStar, collision repair and parts; tools; management topics; service applications and computer issues; and more. It’s a good source for up to date information on every aspect of a technician’s job.


Categories include:

• Diagnostic and Repair Information – Covers repairs on Buick, Cadillac, Chevrolet, Chevy Truck, Chevrolet Volt, Medium Duty Trucks, GMC, Hummer, Oldsmobile, Pontiac, Saturn, and Saab models. (Fig. 8)


F08 forum 2

Fig 8


• General Technical – Including information on general topics, digital pictures, training, OnStar, collision repair, and parts. (Fig. 9)


F09 forum 3

Fig 9


• Tools – Features topics on scan tools, general tools, and the CH-51450 Oscilloscope Diagnostic Kit. (Fig. 10)


F10 forum 4

Fig 10


• Service Manager – Discussions on management insight, customer satisfaction, and warranty issues. (Fig. 11)


F11 forum 5

Fig 11


• Computers – Covers the Service Information, Techline Information Systems, GDS 2, TechLink, PC software, PC operating systems, PC hardware, and the upcoming Data Bus Diagnostic Tool. (Fig. 12)


• General Community – Offers non-technical discussions.


F12 forum 6

Fig 12


Visit the SI forum to share your experiences with your fellow technicians.


– Thanks to Chris Henley



A/C Compressor and Pipe Assembly Changes

Several design changes have been made to the A/C compressor and pipe assembly on the 2015 Equinox and Terrain equipped with the 3.6L engine (RPO LFX). The changes affect 2015 Equinox models built prior to VIN breakpoint F6126358 and 2015 Terrain models built prior to VIN breakpoint F6127049.


Previous Design


The 2010-2014 model year A/C compressor and pipe assembly design can be identified by the small label on the compressor near the pulley. (Fig. 13, A)


The location where the A/C pipe housing mounts to the compressor is rectangular (Fig. 13, B) and the connector bracket, located on the bottom rear of the compressor, for the compressor harness is horizontal. (Fig. 13, C)


F13 ac pipe assembly 1 R

Fig 13


New Design


The new design of the 2015 model year A/C compressor and pipe assembly can be identified by the larger label on the middle of the compressor. (Fig. 14, A)


In addition, the design of the A/C pipe housing has a different shape (Fig. 14, B) and the connector for the compressor is now mounted vertically. (Fig. 14, C)


For more information about the design changes, refer to #PI1312.


F14 ac pipe assembly 2 R

Fig 14


– Thanks to Doug Daugherty

Service Technical College – New Training Courses

There are many training courses to choose from when looking to stay up to date on how to diagnose and repair the latest GM vehicle systems and components. To help technicians learn about the newest courses available through the Service Technical College (STC), TechLink will list the most recently released service training courses (U.S. only). Click the New Service Training link for regular updates.


Following are the latest service technical courses available to technicians through the GM Service Technical College.


Screen Shot 2014-10-08 at 12.06.56 PM


For more information about available service training courses, log in to the GM Center of Learning at and click the Catalog link. Use the drop-down menus to search for courses by delivery type, audience, and category.


– Thanks to Diana Sancya

Rough Idle or Vibration

On some 2014-2015 Corvette, Silverado, Sierra and 2015 Tahoe, Suburban, Yukon, Yukon XL and Escalade models equipped with the 4.3L, 5.3L or 6.2L engine (RPOs L83, L86, LT1, LV3), there may be a condition of a rough idle or a vibration at idle in gear. There will not be any DTCs with this condition.


To correct the vibration, perform the following motor mount alignment procedure.


1. Loosen the engine mount bolts at the frame attachment points. (Fig. 15)


F15 3955251  mount bolts

Fig 15


2. Lift the engine slightly to take the load off the mounts.


3. Use a pry bar to push the mount outboard as far as possible (about 1–1.5 mm) (Fig. 16, left engine mount; Fig. 17, right engine mount); torque the bolts while pushing the mount outboard.


F16 3940842 left side

Fig 16


F17 3940843 right side

Fig 17


4. Tighten the center/upper bolt first, then front, then rear (Fig. 18). Complete this procedure for both left and right mounts.


F18 3955249 bolt 2

Fig 18


5. Lower the engine.


The vehicle may need to be driven for some time to confirm the condition has been eliminated.


– Thanks to Richard Renshaw


Engine Stays Running after Turning Off the Ignition

After turning off the ignition on some 2014 Silverado 1500 and Sierra 1500, and 2015 Silverado and Sierra models, engine may continue to run. If fuse F34UA, located in the Underhood Bussed Electrical Center (UBEC), is removed, the engine will turn off. This is not an intermittent condition.


This condition may be caused by the installation of a fuse in the F26UA and/or F31UA locations in the UBEC. (Fig. 19) These two fuse locations (F26UA and F31UA) are left empty from the factory and should not have fuses installed in these locations.


F19 fuse F34UA

Fig 19


If the truck has the Upfitter Auxiliary Switch option (RPO 9L7), these locations should still be empty.


TIP: If the truck has the Upfitter Auxiliary Switch, refer to the latest version of the GM Upfitter Integration Bulletin 110. The bulletin can be found at Click the Technical Bulletin tab and select “Show all bulletins.”


If fuses have been installed in the F26UA and/or F31UA locations of the UBEC, remove the fuses and discard them. Do not install fuses in these locations.


– Thanks to Jim Will

Rear HVAC Temperature Settings

On 2014-2015 CTS Sedan; 2010-2015 SRX; and 2013-2015 XTS, equipped with the tri-zone HVAC system (RPO CJ4), it may appear that the rear HVAC system at times does not retain the temperature settings after a key cycle.


At every ignition cycle, if the rear controls (Fig. 20) are set to a different temperature than the front HVAC system setting, the rear system will sync back to the front system setting. This will occur whether or not the driver has selected sync on the CUE screen.


This is normal operation. Do not attempt any repairs for this condition.


F20 rear climate control

Fig 20


– Thanks to David Antal

Engine Repair with Crankshaft Replacement

If the crankshaft (Fig. 21) needs to be replaced on 2014-2015 Corvette, Silverado, Sierra; 2015 Tahoe, Suburban, Yukon/XL and Escalade models equipped with the 4.3L, 5.3L or 6.2L engine (RPOs L83, L86, LT1, LV3), be sure to follow these guidelines before completing a crankshaft replacement:


• Complete all appropriate Service Information diagnostics to determine that the crankshaft requires replacement.


• If the engine has bearing and crankshaft damage, the engine should be replaced along with the oil cooler.


• On dry sump engines, the oil tank and lines should also be replaced with the engine.


• Follow the latest version of Bulletin #09-06-04-026G to verify that the ECM calibration is not an aftermarket calibration.


• If a Corvette owner prefers to keep the original numbers matching with the engine, call TAC for repair directions.


 2014 "LT-1" 6.2L V-8 VVT DI (LT1) Crankshaft

Fig 21


– Thanks to Richard Renshaw

Service Know-How

10214.10D – Emerging Issues

October 9, 2014


To view Emerging Issues seminars:

• Log in to

–   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

Service Technical College – New Training Courses

Following are the latest service technical courses available to technicians through the GM Service Technical College.


For more information about available service training courses, log in to the GM Center of Learning at and click the Catalog link. Use the drop-down menus to search for courses by delivery type, audience, and category.


Screen Shot 2014-10-08 at 11.21.43 AM

Bulletin Review – September 2014

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