I just found you guys and I appreciate all the good info in the forums. I can't seem to resolve an issue I'm having with my 03 2500HD Duramax transmission/electronics and I hope someone has seen AND resolved this before.

Truck has 95,000 miles on it and is for the most part stock (maybe that's my problem).

Weeks ago I started getting occasional erratic shifts, usually coming down from 5th to 4th then it would act like it was in tow mode - high rpms before downshifting. Shift were hard into 2nd 3rd, etc.

Flushed transmission and changed filters - no residue to speak of...
Inspected connectors with no obvious issues.

After a couple of weeks of normal shifting, I started getting DTC P0700, U2104, U2105.
If I let the truck cool and clear codes shift goes back to normal for a few days, then the same DTC come back.

I took it in to a local shop and they re-flashed the TCM, checked connections, cleared codes, etc. and they could not make the problem come back. Two more weeks, problem back.

I obviously have a short, failing ECM/TCM/NSBU but where do I start? I've seen this set of DTC's posted a few times but no one ever posts what the actual problem and fix was! Does this mean they are to be driven off a cliff at this point???

I appreciate any advice at this point - hate to put this thing into the dealer's hands. I suspect I'll own a new TCM/ECM and harness.

P0700 - TCM requesting a MIL
U2104 - CAN BUS Reset Counter Overrun
U2105 - CAN BUS Error ECM


gives codes P0700, U2104, U2105
Allison 1000 shift problems

Thank you for your time.

 

I ran into a guy who had the same problem with his '03 this past summer. I think it was a faulty TCM that kept causing all of his grief. Similar issues with shifting out of OD and weird shifting. That's all I know though.

 

I appreciate the info. The problem comes and goes such that it is hard to check the TCM. I found a note with bulletin that said to check the resistance between male terminals 1 and 5 of the grey C1 connector with the C1 removed from the TCM. If resistance shows OPEN, then TCM is bad. Usually the shift problem clears by the time I get back to the house or shop. I guess I need to carry a DMM and pull over to test it while it is acting up.

Does the TCM loose the program after power is removed for an extended time?
Any recommendations on where to order a replacement that is pre-programmed?

 

i would call the dealer and ask ifthere is a recall on it the tcm shouldnt loose it program at all

 

Well, stealer says that there was NOT a TCM recall - there were TCM - re-flash recalls for range issues, but no actual hardware recall that they would admit.
I talked to Allison, they recommended replacing the TCM.

Original TCM part# was 29537441 (mfg. May 3003) new revised TCM part# is 29542725 (mfg. May 2006)

Now back to the shop for a program.

 

I'm back for any new ideas. I had the TCM replaced and re-flashed with the updated Allison TCM. The problem was gone for a few hours, then same codes are back.

NSBU? - no other codes have ever appeared and no abnormal behavior with PRD123 indicator or locks.
Wiring Harness? - I've had it "inspected" but not replaced.
ECM? - weird that I've not ever had any other bad behavior other than P0700, U2104 and U2105.

This is the longest running problem on a Duramax I can re-call without anyone experiencing the same or a shop having a fix...

Appreciate any advice.