[Shadow1]

Looking around on the web it looks like I fried the internal ground in the TCM.

I had been cleaning "grounds" with the batteries connected when the truck started the "no crank" comdition.

 

[Shadow1]

JC1843,

You're right, all the threads I saw on TCM ground issues were the 6-speed.

Thanks for the input.

I'll first see if I now can communicate with the TCM and ECM.

Then check out the grounds on the passenger side rear of the engine block.

Then take a look at the NSBU and ignition switch.

I'll add, 2-weeks ago I had a U1016 P2139 P2140 and no accelerator pedal response. I shut the truck off, restarted and the accelerator pedal was back to normal. The volts for 0% pedal and 100% pedal checked good.

I would think that and the current problem are related?

 

[Shadow1]

With a ground wire attached to the exterior of the TCM:

Truck seems to be operating normally

Communication with TCM/ECM restored

I cleaned the grounds on the passenger side of the block for a 2nd time

The NSBU and ignition switch are fucntioning normally


Can I operate the truck with this ground wire attached to the TCM without doing damage?

Should I replace the TCM?

Is the TCM the same for 2WD/4WD?

Thanks in advance for any inputs

 

[Shadow1]

In my Allison notes I found this test for the TCM (I'm not sure it's for an '05 LLY).

With my DMM I checked the resistance between male terminals 1 and 5 of C1 (Grey) connector at the TCM (not the wiring connector) with the TCM out of the truck.

I got 0.0 to 0.1 ohms resistance, so the TCM passes this test if I got it right?

Now I don't know what to do next?

Thanks for any inputs in advance.

 

[Shadow1]

I found this bullitin that BoostEED posted:

Subject: Repeat TCM Failures with Possible Multiple DTCs

Models: 2001-2005 Chevrolet Silverado

2001-2005 GMC Sierra

with LCT1000 (RPO - M74) Transmission

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in the PI.
Condition/Concern:


The Allison LCT1000 may experience a condition in which the TCM has repeat failures. Any of the following (but not limited to) DTCs may be set: P0561, P0562, P0880, P1571, P1760, U1000, U1301, U1305, U2105.
Recommendation/Instructions:


Using a DVOM, check the resistance between male terminals 1 and 5 of the C1 connector (grey) at the TCM, with the wiring harness C1 connector removed from the TCM. If this measures to be an open, the TCM must be replaced. The negative battery cables must be checked for being loose.
If the vehicle is experiencing a DTC P0562 and the above check does not reveal the problem, the ignition switch should be replaced.

The following grounds should be checked:
6.6 LB7 Diesel Engine
1. G104, G105 - Left Battery Ground
2. G102 - Right Battery Ground
-----------------------------------------------

I've double checked these grounds and also checked for ground on the wire connector side of terminal 1 and 5 and they look good at .5 ohms.

Since I have continuity between terminals 1 and 5 of the TCM I suppose my TCM is good.

Anybody have any ideas?

 

[Shadow1]

I've been driving the truck now for over 3 weeks, problem free, with a ground wire attached to the TCM case.

Disconnect this ground wire and no start, lots of class 2 data problems, no comms with ECM/TCM, reconnect and all is well.

I have .58 ohms from C1 Gray wiring harness female pins 1 and 5 to ground.

0 ohms C1 pins 1 to 5.

0 ohms C1 pins 1 and 5 to TCM case.

So it seems I don't have a ground through the C1 (pins 1 and 5) with the connector pushed into place - the pins look clean, not pushed back, no different than the rest of the pins in C1.

I'll keep checking the pins and driving the truck and see what I have.