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Hal
Hal, Chevy Master Tech
Category: Chevy
Satisfied Customers: 1020
Experience:  ASE and Chevy Master , 31yr Dealership exp,
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I have a 2001 GMC Yukon Denali. It has longstanding intermittent

Customer Question

I have a 2001 GMC Yukon Denali. It has longstanding intermittent electrical issues. The symptoms are: Several gauges in the dash go to their "off" position intermittently including: fuel gauge, temperature gauge, battery voltage. In addition, OnStar LED will show Red. I purchased an OBDII scanner, which doesn't work when this happens.

I believe this is an issue with the bus between the various modules (PCM, BCM, Air Bag Module, OnStar module). I was able to confirm this by isolating modules via Splice Pack 205, where the modules connect to each other. The Bus (or level-2 communication I think they called it) would be locked up until I disconnected the PCM and the BCM from everything. After I disconnect these two, and connect everything back together, the system would operate correctly. I suspect either the BCM or PCM. I have had the BCM reprogrammed at a repair shop, which cost me $100, didn’t fix the issue.
What do you recommend? Replace BCM? PCM? Something Else?
Submitted: 4 years ago.
Category: Chevy
Expert:  Hal replied 4 years ago.

Hi my name isXXXXX

I feel your frustration with this kind of concern. You are correct, the concern is with the Class 2 communication. Unfortunately this is one of the most difficult concerns to Isolate.

Any one of the modules on the class 2 line can be the culprit. You have a good start in going to splice pack 205 , and isolating it down to a BCM or PCM.

Reprograming does not correct a hardware issue with a module witch is usually the case in these matters.

If I were at this point I would check or rerun the communication line to the modules first.

If that did not correct and I did not find a definite short to ground, Next make sure there are no after market devices hooked in any where. Connections to data sources powers and grounds to modules will make them do weird things. But I don't think that is your concern here.

I would replace the BCM they have had more issues than the PCM. Plus the BCM is responsible for the body functions that your having troubles with.

Look around the left inner fender for the most likely spot for the communication line to be shorted that goes to ECM. It is most exposed and I have found allot of problems in that area.

Hope this is the info you were looking for. HAL

Customer: replied 4 years ago.
I will accept the answer, but just a few more points of clarification please. For looking for the most likely spot for the communication line to be shorted, can you provide a bit more detail in terms of where to look? Do I just find the ECM, then the harness that feeds the ECM and look for a short? If I find a short or bad harness, I guess that will need to be replaced first?

Thanks
Expert:  Hal replied 4 years ago.

Yes I can thats not a problem.

The ECM should be located on the front left inner fender. Follow the harness up to the under hood fuse block. This is where I find most wiring issues. The harness will go under the UHFB and into the vehicle though the pass through grommet lower left of fire wall. It comes into the vehicle and up and over the emergency brake pedal. ( this is another location to inspect the harness. The BCM should be left of the steering column, or just below the column.

All you need to do is make sure the harness is not shorted to ground. Go to the splice pack as you have already done. find the wire to the ECM and BCM. Unhook the BCM and ECM and ohm out the wire. If you have continuity to ground then the circuit is shorted. If not then it is the module. This is exactly how I have to diagnose these type of problems.

Hears the catch. the condition MUST BE PRESENT to find it. As i stated before these types of concerns are very difficult to isolate unless they are hard failures.

If you need wire colors or terminal locations Let me know.

PS the reason I said replace the data circuit is because if it is shorted , it is sometimes easier to just replace the wire that it is to locate the short. At least it is for me.

Hope this info is what your looking for.

Hal, Chevy Master Tech
Category: Chevy
Satisfied Customers: 1020
Experience: ASE and Chevy Master , 31yr Dealership exp,
Hal and 4 other Chevy Specialists are ready to help you
Customer: replied 4 years ago.
Thanks, XXXXX XXXXX very helpful.
Expert:  Hal replied 4 years ago.

Your welcome, and thank you for using just answer.

Thanks again Hal

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