Truck lost communication with TCM.

Jan 7, 2023
1
0
1
55
Winnemucca, NV
My 2008 Chev Duramax 6.6L with Allison Trans is stuck in 2nd or 3rd gear. My superchip that I use to read DTC's comes up with " lost comm with TCM" I have another TCM from same year, make & model...do I need to program it some how ? Need help.
 

Ron Nielson

Active member
Oct 11, 2009
702
118
43
Berryton, KS
You may or may not need a new/repaired TCM. The 1st thing to do is to make sure the TCM has power and is grounded. You will need a wiring diagram and a test light and DVM. If you aren't comfortable with doing the work yourself, you will need a shop to determine if the TCM is really dead. It is not at all uncommon to have circuit problems that cause this and you'd sure wouldn't want to pony up for a TCM repair if you only have a bare wire somewhere.
 

DieselsSafeSpace

aka PowerHustler
Dec 20, 2020
1
0
1
Programming is done with tis2web and a tech2. Diagnoses is a must. If your still having issues let me know and I'll provide a wiring diagram.
 

Ron Nielson

Active member
Oct 11, 2009
702
118
43
Berryton, KS
Since you have another 20008 TCM, you could plug it in and see if you have communications or not. If you do, you have some info about your existing TCM. If not, it was worth a try. I think you need to get the replacement married to your truck after you see if it works/communicates.
 

Cougar281

Well-known member
Sep 11, 2006
1,759
216
63
St Louis, MO
Since you have another 20008 TCM, you could plug it in and see if you have communications or not. If you do, you have some info about your existing TCM. If not, it was worth a try. I think you need to get the replacement married to your truck after you see if it works/communicates.
Tcm should just be plug n play.

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