TCM Lost communication. Am I missing something or is it just dead?

[[email protected]]

I'll first tell what I have and then what it is doing. Let me know if I left something out or you need more information. This is my first swap so I'll do my best.

I purchased a complete 6.0 LY6 with a 6L90e and transfer case out of a wrecked 2009 2500 HD. I heard the engine run, since it was wrecked it was not shown to drive or shift. I assumed since it was wrecked they were driving it when it happened. I also received the E38 ecm, the wiring harness, and the fuse panel. All accessories, minus MAF and air box also came with it. I installed the combo using the factory wiring harness and ECM into a 94 Z71. I cut the fuse panel out as I would not be using 90% of it. I assembled and put in a new panel with relays and fuses for fuel pump and engine power requirements. I read the ecm and made only the needed changes. Shut off VATS, turned off statrer checks, secondary o2, evap,and fuel pump relay settings. None of those are in the old truck and would not be needed. The engine starts and runs fine, I am pretty happy with it. I don't recall ever seeing a TCM in the software though. On the first drive I could tell it was in limp mode. I read the codes with a reader i have, not the scanner. I got a TCM and BCM lost communication. I don't have a BCM so that is expected. Now on to finding the TCM problem.

Here is what I have tested.

I have verified the red (pin 4 I think) to have 12v both connected to TCM and not connected to the TCM with key on and off.
I have verified the pink wire (pin 12 I believe) to have 12v both connected tot he TCM and Not connected with only the key on.
Testing this connected seemed important as once the TCM pulls power it should maintain good power supply.
I have verified black wire (pin 5) is a good ground
I have tested both the GM LAN wires from ECM to the trans and from the trans to the body connector are good.
I have tested the serial wake line is good. no voltage applied on it's own.

I have my OBD port connected to the GM LAN wires that come from the trans to the old connector that used to go to the BCM. I have cut off that connector and used those lines. So from what I can tell it goes from OBD port to trans, from trans to ECM. I have good communication to the ECM. This tells me the connector is at least in there that well. I have cleaned and made sure it is in all the way.

I have read somewhere that I would need a 120ohm resistor ont he GM LAN line that used to go to the BCM. I put that on, no change.
I also read that the wake line should have voltage, supplied by the BCM which I don't have, I applied 12v to that line and no change.

Does anyone know of anything else I could be missing or is it possible that TCM is just bad?

Any help or advice is always appreciated.

Thanks.

[Guy With A Chevy]

I would try the seeing if another vehicle recognizes the tcm

[blindsquirrel]

I would try the seeing if another vehicle recognizes the tcm

That would be really difficult, seeing as the 6L's TCM is built into the valve body.

[Guy With A Chevy]

Ouch

[[email protected]]

Just to post a resolution.

The issue was the TEHCM. I ordered a reman from Street Smart. Got it installed and the transmission connected and is shifting fine now. It could use a shift tune, but that's for another time.

[PGA2B]

Take a look at the Bluecat Trans Tool. That will get you going.

https://forum.hptuners.com/showthrea...Table-Software