Recent discovery of SatbiliTrack failure Mode

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MolaKule

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This past winter we had numerous intermittent StabiliTrack codes. Sometimes the steering wheel position sensor or wheel speed sensors and connectors can get flaky and throw these codes, but no fault was found with these.

GM had issued a TSB for this problem and reprogramming, but none of these codes made any sense.

The wife came hone Saturday after her trip to her mom's and said the '08 TrailBlazer had no AC, no PWR Windows, no guages, no radio.

I checked all of the pertinent fuses in both the Engine Compartment and those underneath the back seat and no blown fuses.

I hooked up my OBD-II scanner and no talky to the PCM, no codes.

I was fearing an Instrument Cluster and or CAN bus problem.

I unhooked the various Control Modules one-by-one.

It turned out that the OnStar module was partially shorting the CAN bus and pulling down voltages from the PCM.

Disconnected the OnStar module and wolla, everything worked again. Since we don't use it and never did, I did not replace it with a new $600.00 unit.

The CAN bus is great when you have various control modules scattered around the vehicle, but it only takes one module with a flaky CAN transceiver or cable fault to bring it down. When this happens, the PCM goes into its Default/Open-Loop mode so one can still drive the vehicle home or to the repair shop.
 
Last edited:
Originally Posted By: MolaKule
This past winter we had numerous intermittent StabiliTrack codes. Sometimes the steering wheel position sensor or wheel speed sensors and connectors can get flaky and throw these codes, but no fault was found with these.

GM had issued a TSB for this problem and reprogramming, but none of these codes made any sense.

The wife came hone Saturday after her trip to her mom's and said the '08 TrailBlazer had no AC, no PWR Windows, no guages, no radio.

I checked all of the pertinent fuses in both the Engine Compartment and those underneath the back seat and no blown fuses.

I hooked up my OBD-II scanner and no talky to the PCM, no codes.

I was fearing an Instrument Cluster and or CAN bus problem.

I unhooked the various Control Modules one-by-one.

It turned out that the OnStar module was partially shorting the CAN bus and pulling down voltages from the PCM.

Disconnected the OnStar module and wolla, everything worked again. Since we don't use it and never did, I did not replace it with a new $600.00 unit.

The CAN bus is great when you have various control modules scattered around the vehicle, but it only takes one module with a flaky CAN transceiver or cable fault to bring it down. When this happens, the PCM goes into its Default/Open-Loop mode so one can still drive the vehicle home or to the repair shop.


The NSA will be around to patch it back up. After all.....How will they monitor you, with the OnStar nonop?
 
Interesting point and information; thank you.

My mother has a 2007 Equinox she's had since new, and it has unpredictably thrown StabiliTrak codes since it was a year or two old. I do not think hers has OnStar, but perhaps I can use the CAN bus clue to find something causing it.

Most recently, my father and I poked around to diagnose increased oil usage. We re-connected some loose vacuum hoses and changed the front spark plug wires. It immediately through a StabiliTrak code when re-started. This led me to realize the StabiliTrak system itself likely had nothing to do with it.
 
I know that controller area networks are cheap and reasonably simple, but there are better, albeit more expensive network solutions that don't fail this way.
 
I used to have a can bus problem but then I got married and had a kid and had to get a real job, so no more can bus for me. When I retire though, I'm moving to Colorado and it's on!!!! You can have all the can bus you want there!!!

EDIT - I should have made the move to Colorada an off topic disclosure!!!
 
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Originally Posted By: Wheel
I know that controller area networks are cheap and reasonably simple, but there are better, albeit more expensive network solutions that don't fail this way.


True, but this is a Vehicle CAN Bus conforming to SAE J1939.

https://en.wikipedia.org/wiki/SAE_J1939

Not exactly a fault Tolerant bus.

Recall in this case the OnStar module was doing two things, pulling down the Voltage supply line AND shorting the CAN Bus.
 
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Originally Posted By: MolaKule
Originally Posted By: Wheel
I know that controller area networks are cheap and reasonably simple, but there are better, albeit more expensive network solutions that don't fail this way.


True, but this is a Vehicle CAN Bus conforming to SAE J1939.

https://en.wikipedia.org/wiki/SAE_J1939

Not exactly a fault Tolerant bus.

Recall in this case the OnStar module was doing two things, pulling down the Voltage supply line AND shorting the CAN Bus.


Actually, J1939 is usually only used in the heavy truck and off highway markets. I believe GM is following ISO J1850.
 
Originally Posted By: DriveHard
Originally Posted By: MolaKule
Originally Posted By: Wheel
I know that controller area networks are cheap and reasonably simple, but there are better, albeit more expensive network solutions that don't fail this way.


True, but this is a Vehicle CAN Bus conforming to SAE J1939.

https://en.wikipedia.org/wiki/SAE_J1939

Not exactly a fault Tolerant bus.

Recall in this case the OnStar module was doing two things, pulling down the Voltage supply line AND shorting the CAN Bus.


Actually, J1939 is usually only used in the heavy truck and off highway markets. I believe GM is following ISO J1850.


Ok, actually I think GM is using J1850 for the standard OBDII diagnostic communications, but has their own GMLAN for internal CAN communications and systems controls.

http://www.acdelcotechconnect.com/pdf/imtn_V16I109.pdf
 
That's what I was getting at, CAN isn't fault tolerant. It has no intelligence in it to prevent one device from halting good communication. These networks could be built in a fashion more like a good TCP/IP/packet switching computer network.

This could provide some fault tolerance and security that is lacking.

The downside would be somewhat more cost.
 
Originally Posted By: DriveHard
Originally Posted By: DriveHard
Originally Posted By: MolaKule
Originally Posted By: Wheel
I know that controller area networks are cheap and reasonably simple, but there are better, albeit more expensive network solutions that don't fail this way.


True, but this is a Vehicle CAN Bus conforming to SAE J1939.

https://en.wikipedia.org/wiki/SAE_J1939

Not exactly a fault Tolerant bus.

Recall in this case the OnStar module was doing two things, pulling down the Voltage supply line AND shorting the CAN Bus.


Actually, J1939 is usually only used in the heavy truck and off highway markets. I believe GM is following ISO J1850.


Ok, actually I think GM is using J1850 for the standard OBDII diagnostic communications, but has their own GMLAN for internal CAN communications and systems controls.

http://www.acdelcotechconnect.com/pdf/imtn_V16I109.pdf


Thanks for the Additional Info.

Yep, Bosch originally developed the CAN but everyone has their own flavor of SAE J1939.
 
Originally Posted By: Wheel
That's what I was getting at, CAN isn't fault tolerant. It has no intelligence in it to prevent one device from halting good communication. These networks could be built in a fashion more like a good TCP/IP/packet switching computer network.

This could provide some fault tolerance and security that is lacking.

The downside would be somewhat more cost.


Agreed, in the Aerospace industry we designed-in some very good high speed FT buses.

Maybe someone did an analysis and decided this was good enough based on times to fault occurrence.
 
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