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Discussion Starter · #1 ·
I have an 09 duramax turbo diesel with the allison 1000. I'm having trouble with the truck when I'm driving. Stabilitrak light will pop on then The tranny acts like it's downshifting out of OD back and forth and the the gauge cluster starts going crazy. Every gauge drops to nothing except for the voltage gauge. No problem shifting except that. Also goin down the road the doors will lock and unlock. Is this some kind if electrical problem or is there an explanation that I can fix quickly?
 

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Mine has just done the same thing.
what Chevy dealership done to mine is check the pigtail lead on the back right hand corner of transmission. They unhooked the wire harness, and there was fluid on the outside of the bulkhead, and wicking into 24 pin wire harness. There should not be any trans fluid leaking threw bulkhead. shorting the wiring and communication to the TCM

long and short of it is the internal wire harness has to be changed. Also since I am over 100k miles they said to change out the PRNDL switch.

At least that is what they are telling me.
I have bought the PRNDL switch and the internal harness.
Going to give it a shot.
 

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Not saying that the pigtail mentioned isn't the issue, but the gauges dropping to zero, and the instrument cluster going crazy happens occasionally on half ton GM trucks also. Even the 4L80 equipped ones. Just mentioning, that's not an issue strictly limited to diesel units, or the Allison equipped models.
 

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Discussion Starter · #5 ·
When that happens, the doors lock/unlock, hard downshifts and acts like it's kicking in and out of overdrive. Idk bro. Guess ima take it somewhere. I can't figure it out.
 

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Definitely sounds like an electrical demon of some sort to me. Maybe it is locking and unlocking the Torque Converter? Which would point to maybe and issue with the tow haul feature....caused by an electrical gremlin.
 

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I would start by checking battery connections and grounds. You have an electrical issue you need to chase down.

I'm sure someone will jump in to talk about possible spots to check.
 

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Mine ended up being the internal harness (which was leaking ATF in the main harness)
and it shorted out the TCM.(found that out after above repair)
also purchased the PRNDL switch, since I was in there and they say to replace in any Allison over 100k.

Bought TCM because of error code: U0101 after internal harness replacement was done.

Had it programmed, and it seems to be good to go (for now) got about 150 miles on it after repair.

I think I am going to wither use the other clip mount in the top of the TCM as a secondary mount, or I saw on here there was a post about relocating to the top cover of the fuse box with velcro.
That way if I replace serp. belt with a non GM it should not interfere.
 

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Discussion Starter · #9 ·
Well I put a new tcm on it a few months back. I hit a famous south carolina pot hole and broke the clip that holds it in place. Which resulted in it falling into the fan belt that didn't end well. After the replacement and getting it programmed it drove fine until a couple wks ago.
 

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Well I put a new tcm on it a few months back. I hit a famous south carolina pot hole and broke the clip that holds it in place. Which resulted in it falling into the fan belt that didn't end well. After the replacement and getting it programmed it drove fine until a couple wks ago.
Check behind the rear seat on the driver side for water leaking in from your third brake light it runs down into the remote control door lock receiver it's for keyless entry and tire pressure monitoring system ! Anyway the water gets into that module about the size of a deck of cards or a little bigger and shorts out the data line and causes all kinds of problems ! There's a bulletin from Gm about this condition , the instrument cluster , door lock module , body control module are all on that data line so you'll see all kinds of crazy stuff happen !
 
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