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Allison OEM Discuss repairing & maintaining an OEM Allison automatic transmission.

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Old 11-20-2019, 07:36 PM   #1 (permalink)
GarrettM2004
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TCM Communication

Hello I’ve got a 2004.5 duramax with the Allison 5 speed....I have a communication issue...I’ve pulled the harness from the transmission, inspected harness and checked for resistance. All was good replaced NSBU switch, replaced internal wiring harness and all solenoids and pressure pack. Then ordered a brand new preprogrammed TCM with factory calibrations....still nothing still have an active code (U1071) “loss of communication with TCM”

Any ideas in a right direction would be much appreciated

-Garrett

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Old 11-20-2019, 07:42 PM   #2 (permalink)
OkDually
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Welcome to DieselPlace
I moved your post over to the "Allison OEM" section of the forum for appropriate views and responses



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Old 11-21-2019, 10:09 AM   #3 (permalink)
Rvn4me
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Quote:
Originally Posted by GarrettM2004 View Post
code (U1071) “loss of communication with TCM”
Does your truck start?

U1071 This code hasn’t ever been mentioned on none of the major diesel sites. DieselPlace, Duramaxforum, DuramaxDiesel, Dieselpage, Etc...

Allison master code list defines U1071 as this.
ALLISON 1000 Code (DTC) U1071 SCP (J1850) Invalid or Missing Data for Engine Sensors

GM’s code list is this.
Definition of check engine code U1071:
GM:
Loss of Serial Communications for Class 2 Devices

What I’m trying to say I don’t think U1071 is your correct code.

You sure you don’t have this code?
U0101 Lost Communication with TCM

This is how you test your TCM
Test for continuity between pin 9 and 69.

Recommendation/Instructions:
1) If the circuit between pin 9 and 69 is open, then the TCM has been damaged from some external source shorting to the heatsink of the TCM.
2) Inspect for the source that shorted to the TCM heatsink.
3) Eliminate or repair the source or condition that caused the damage.
4) Replace damaged TCM after the condition that caused the TCM damage has been corrected.
Note: Visual surface pits and carbon deposits are typically found on the TCM heatsink when high energy arcs are generated by shorts between the heatsink and battery power.
If continuity exists between pin 9 and 69, then refer to steps in eSI for "No engine crank" and/or "No communication"

Last edited by Rvn4me; 11-21-2019 at 10:37 AM.
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Old 11-21-2019, 10:47 AM   #4 (permalink)
Rvn4me
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Have you looked at the wiring harness rubbing the inner fender well. This area has been know for lots of communication codes TCM and transportation hick-ups.
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Old 11-21-2019, 11:01 AM   #5 (permalink)
GarrettM2004
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Sorry it is the u0101 code not u1071, all harnesses from the fuse junction box down frame and to transmission have been inspected
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Old 11-22-2019, 09:08 AM   #6 (permalink)
Rvn4me
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A lot of people say they have inspected and found nothing. Then they open up there harnesses an found there problem.

I hate repeating myself but have you done this?
I know you put in a new TCM but I’m still curious If you have continuity between pins 9 and 69 at the TCM.

Seems like I’m pulling teeth.
What are all your symptoms please. Does it start? Does it drive normal, do you have Range Shift Inhibited, when did this start, does this when driving through water or a bump, did you just add something, any other codes, is your reader able to read TCM codes, etc...

I think you best option is your dealer. Working on those computer bus lines, you really need full wiring diagrams and a dealer level scan tool to analyze modules for correct communication and finding of flaws. Otherwise, good luck ohming the resistance on all the wires and connectors, and realize you HAVE to do dynamic loaded testing of them, not just static test with a volt meter

Last edited by Rvn4me; 11-22-2019 at 09:38 AM.
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