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Juan Crespo
Juan Crespo, Tech Trainer
Category: GMC
Satisfied Customers: 1523
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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I HAVE AN ON GOING U0106 CODE ON 07 GMC DURAMAX 2500, THE

Customer Question

I HAVE AN ON GOING U0106 CODE ON 07 GMC DURAMAX 2500
JA: Just to clarify, what's the exact code? And have you tried to reset it?
Customer: THE VEHICLE WILL RUN FINE AND WHEN IT GETS HOT IS WHEN WE HAVE THE COMMUNICATION LOSS TO GP MODULE
JA: What is the model/year of your GM?
Customer: 2007 GMC 2500 DURAMAX
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: WE HAVE REPLACED GLOW PLUGS(IT HAD P0672 CODE)
JA: Anything else you think the mechanic should know?
Customer: WE HAVE REPLACED GP MODULE ALSO
Submitted: 7 months ago.
Category: GMC
Customer: replied 7 months ago.
THE VEHICLE ORIGINALLY CAME IN WITH SEVERAL CODES THAT HAVE GONE AWAY SINCE REPLACING THE GP MODULE AND ALL GLOW PLUGS(U0101, P0700, P2544, P0672, P0087, U0100 WERE THERE AND ARE NOW GONE) WE RAN JUMPER WIRES FROM PCM TO GPCM FROM COMMUNICATION SERIAL WIRES AND TRUCK RAN FINE ALL DAY AND AT END OF DAY IS WHEN WE LOST COMMUNICATION WITH GPCM. VEHICLE STILL STARTS AND RUNS BUT WE CANT GET THE LIGHT TO STAY OFF.
Expert:  Juan Crespo replied 7 months ago.

Hi there.

Taking into consideration the fact that this type of code will set in a module other than the one with a communication failure, plus you having replaced the glow plug module, plus by-passing any possible issues with the wiring with the jumpers, I'd take a close look at the BCM as the possible culprit. Do you have access to a Tech-II or equivalent scan tool?

Customer: replied 7 months ago.
I do
Customer: replied 7 months ago.
loss of GPCM communication goes through BCM?
Expert:  Juan Crespo replied 7 months ago.

BCM is the boss module. All communications go through it. Can you communicate with it and see what happens when communications is interrupted with the GPM?

Customer: replied 7 months ago.
sure let me try
Expert:  Juan Crespo replied 7 months ago.

It's just an educated guess based on the fact that the BCM is the gateway for the high and low speed GMLAN networks - I mean, you have already done eliminated the GPCM and the wiring...

Customer: replied 7 months ago.
I don't show GPCM going through BCM...am I incorrect in that?
Expert:  Juan Crespo replied 7 months ago.

No, you're not incorrect in the sense that the GPCM is not controlled by the BCM. Thing is we have a communications code not a circuit failure code, so what we need to find out is why the GPCM is dropping off the BUS, and we know the BUS goes not only from the GPCM to the ECM, but to the BCM, EBCM, etc. as well. When you ran wires from the ECM/PCM to the GPCM, you basically bypassed only that part of the BUS. We need to find out if communications were interrupted somewhere else.

I've been retired for a while, but if I remember correctly, there was a way to set the Tech-II to display a map of the LAN network. Can you do that or am I wrong?

Customer: replied 7 months ago.
I am not sure. Let me talk to my tech in the morning as our shop is closed now.
Expert:  Juan Crespo replied 7 months ago.

Looking closer at the LAN diagram (see attached graphic), the TCM comes first between the ECM and the GPCM, so that might also be a point of interest in your diagnosis.

I'm logging out for today as well. I'll be back online tomorrow and every other weekday from 2 to 8 PM EST.

Best Regards.

Customer: replied 7 months ago.
We looked this morning based off the diagram you sent at the wires that show to go from the BCM to GPCM. They don't match the colors to the one we have here in order to check continuity. We can clear codes and start it and no lights. After running check engine and glow plug lights come on with that same GPCM communication loss.
Expert:  Juan Crespo replied 7 months ago.

As far as I know, GM uses Tan and Tan/Black wires for its high speed bus - check the wires connected to terminals 6 and 14 of the data link connector to verify and let me know what color wires are there.

Erase all codes and run the engine until the code sets again, then upload the freeze frame data so I can get a better idea of how and when the code is setting.

Customer: replied 7 months ago.
6-TAN/WH 14-TAN
Expert:  Juan Crespo replied 7 months ago.

OK. We seem to be having a communications issue... how about uploading that freeze frame data? I mean, I want to help you, but the only way I can do so is if you provide the information I request. For example, you were going to check with your tech to see if your scan tool could display/map all the modules on the network. Can it do that?

Customer: replied 7 months ago.
HE HAS A TECH II AND WE LOOKED THIS MORNING BUT IT DIDN'T GIVE A LOT OF DATA. I STILL NEED TO PULL FREEZE FRAME. I HAVE MY TECH GOING BACK AND FORTH ON JOBS RIGHT NOW BUT THIS ONE IS DEFINATELY PRIORITY.
Expert:  Juan Crespo replied 7 months ago.

OK. I'm afraid there isn't much I can do until I get that information.

Customer: replied 7 months ago.
If I clear the codes and restart the truck, engine and glow plug lights stay off for a while.
Customer: replied 7 months ago.
Normally both lights come on together. I went and checked while running and now just the glow plug light is on.
Expert:  Juan Crespo replied 7 months ago.

OK. Unfortunately, that alone doesn't help me formulate a diagnosis; I still need the information I previously asked for.

Customer: replied 7 months ago.
Yep of course. Now engine and GP lights are on so let me get the freeze frame.
Expert:  Juan Crespo replied 7 months ago.

Don't forget about the Tech-II stuff... I need ALL the information I previously requested

Customer: replied 7 months ago.
The display map of all the modules on the network? I'll see if his can do that and get the freeze frame to start for sure.
Expert:  Juan Crespo replied 7 months ago.

If his can't do that, then it is not a Tech-II like you had stated it was.

Customer: replied 7 months ago.
GM TECH 2 SCANNER BUT IT DOESN'T LOOK LIKE HIS CAN DO THAT.
ENGINE SPEED 645RPM
ECT SENSOR 185F
IAT SENSOR 2 152F
BARO 82KPA
MAF SENSOR 30.69 G/S
AMBIENT AIR TEMP 78F
DESIRED EGR POS 3%
EGR POS VARIANCE 0%
ACTUAL FUEL RAIL PSI 4083.2PSI
IGN 1 SIG 13.9V
APP SENSOR 1 0%
APP SENSOR 2 0%
ENGINE RUN TIME 9:34
Customer: replied 7 months ago.
THERE'S A BETTER SNAP SHOT
Expert:  Juan Crespo replied 7 months ago.

Are you serious? That data is for code U0101... what happened to U0106?

Customer: replied 7 months ago.
U0106 IS STILL THERE AND THAT WAS OFF GLOW PLUG MODULE AND ECM, SAME INFO
Expert:  Juan Crespo replied 7 months ago.

It looks like I can't help you. I'll opt out so others may try. Do not reply until another expert chooses to respond or the site will cycle this back to me.