Electrical nightmare. Please Help. - Chevy and GMC Duramax Diesel Forum
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post #1 of 3 (permalink) Old 10-29-2019, 02:48 AM Thread Starter
Join Date: Jul 2018
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Electrical nightmare. Please Help.

I’ve been chasing an electrical issue on my 13’ LML for close to a year now. It is temporarily losing communication with ECM, PCM, BCM, & TCM. Whenever I hit a bump in the road the speedometer goes crazy and bounces everywhere and “service traction control” “service stabilitrak” “park assist off” messages will flash while the gauge is bouncing. Sometimes while driving and not hitting any bumps, I’ll look down at the speedo and see it barely bouncing back and forth (like not even 5mph difference) I’ve recently noticed that when it acts up my radio will get quiet by itself and then return to the volume I had it at. I also don’t bother to use the cruise control anymore because it will kick out by itself when I hit a bump. I’ve replaced the BCM, TCM (seperate issue), both negative battery cables that bolt to the engine block. I’ve pulled the fuse box apart and cleaned all the connectors and applied di-electric grease. I’ve cleaned every ground I can find and load tested the batteries separately. They both checked good. I finally gave up and took it to the dealership. They got GM involved and said GM recommended replacing the output speed sensor on the transfer case. I let them do it. $420 later and as soon as I pulled out of the dealership and hit a bump in the road it went crazy. I’m at a complete loss and am contemplating getting rid of it. Any advice is appreciated
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post #2 of 3 (permalink) Old 10-29-2019, 03:50 AM
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Location: Maurice, LA
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It sounds to me like you have a chaffed wire that is intermittently grounding itself when you hit bumps.

The solution is probably going to be slow and painstaking..............looking at each and every place where any wiring bundle comes near any stationary piece of anything else and looking for that chaffed wire. Id probably start at that large wiring connector on top of the engine.

IF you decide to disconnect anything, Id suggest taking off Both of ur Neg battery cables first. That way no shorts, no sparks, no damage to expensive electrical equipment.

It could also be a bad ground, intermittently bad, there are many, I think 13 but I dont' know where they all are

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post #3 of 3 (permalink) Old 10-29-2019, 11:29 AM
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Location: Alaska
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theres a couple common wear through points on the engine harness under the hood. If you rub a data wire through it could periodically ground out which could cause your errors in communication and other data module issues. I would look over the main engine harness for wear, specifically around the alternator and other brackets where it may rub.

2015 Chevy Silverado 2500 HD 6.6L LML
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