LMM: 911 need help

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butch2000

New member
Jun 19, 2012
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ok guys need your help here , 08 LMM today the trans started acting funny , tons of codes , do a trans relearn trans shifts great till I shut the truck off , when re started it will not move ?
P0218
P0711
P0712
P0713
P0561
p0562
p0881
p0882
P0751
P0752
P0634 this one I think is the problem ? TCM over heat ?
P0881
P0979

Could the TCM be bad ? so hot you cannot touch it , mounted in the stock location fan shroud ? I have heard when the computer goes south it throws random codes ?
does it have to be replaced and flashed at the dealer ? thanks
 
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Ron Nielson

Active member
Oct 11, 2009
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Berryton, KS
If you need a new TCM, you will have to have it programmed (flashed). Any reason that the TCM should be so hot? Anything blocking airflow to the TCM? Clean the TCM if dirty. 140 degrees is the magic temp to set the code.
 
clrussell

clrussell

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Sep 23, 2013
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butch2000 said:
anyone have a pic of the nsbu switch on the 2008 Allison ? I think it is now on the steering column ? not on the side of the trans anymore ?
Click to expand...

It's internal of the allison... You probably don't need to change one
 
clrussell

clrussell

pro-procrastinator
Sep 23, 2013
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butch2000 said:
clrusslle, why is that ?
Click to expand...

Honestly if you think the nsbu can have the possibility of being on the steering column then you don't have the skill needed to change the actual nsbu internal of the trans.


Unplug the big connector. Clean it, plug it back in and clear codes. Go from there.
 
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butch2000

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Jun 19, 2012
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already did that , it was clean , no fluid , clear the codes , works great till the P0708 , and engine light come on then goes to limp , and gets worse from there , have not boosted anything with it , and I was having a brain fart about the NSBU location , LOL, it was a long day !
 
DAVe3283

DAVe3283

Heavy & Slow
Sep 3, 2009
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Boise, ID, USA
Hey, now, we do this on our own time, because we enjoy it. No one here is obligated to help anyone, and just because you don't get a response immediately doesn't mean we won't help (not that we have to anyway).

The Allison is a complex transmission, and probably the least understood piece of these trucks by most members, myself included. There are a couple of experts here that know it inside and out, but again, they help on their time when they feel like it.

From what little I know of the trans, and the P0708 code, it sounds like a wiring or harness issue. If there are shorts in the harness it could cause the TCM to overheat, and throw a bunch of other codes. If I were you, I would go over the harness with a fine-tooth comb, using a digital multi-meter to verify every wire is working and not shorted. If that looks OK, might be worth acquiring a new TCM to try out.

The problem is this issue sounds intermittent and is unusual, so it is hard to correct without being there in person. You might just have to take it to a competent transmission shop.
 
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butch2000

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Jun 19, 2012
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I never said anyone was obligated ? and you are right , you can pick and choose who want to help as well , then that should be a private forum , sounds like a ford forum ?
I do appreciate the help when given , thanks and have a great day !
 
T

TBone

New member
Dec 9, 2008
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Just a question have you changed out your serpentine belt with an aftermarket There is a GM service bulletin that basically says to check if owner has replaced the serpentine belt with an aftermarket , Some aftermarket belts have a compound in them that makes them prone to slippage thus generating static electricity. According to the bulletin it usually causes problems with the TCM. I just responded to some elses post on another thread about this same issue.
 
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