LB7: Trans Limp and P1781 / P0700 under load acceleration

[db131994]

The plot thickens...

Ok, after I put the TCM back in and hooked everything up, I hooked up my OBD2 blue tooth and pulled up my Torque App. It pulled up the P0700, and a P0776 (Pressure Control Solenoid B)… After that, I hooked the tuner back up to see what codes it may have. It had the P0700 as it did after the trans lockdown and that's all it had when I checked this morning on my way to work... Plus, it had P1781, U1000, and U2106. Since I had the TCM unplugged and cycled the key to on and off, I'm not sure if that could have caused the P1781, U1000, and U2106 to trip as "false positives..." To me, the one that's interesting is the P0776. I have no idea if it has been there before. I haven't used the Torque app, since I could pull codes from the tuner... Obviously that's gonna change...

Hopefully these clues are starting to paint a picture for someone, because all I see are swirl marks...

The logic part of it to me says the Pressure Control Solenoid makes more sense. 1 - The lock down happens at a fairly consistent set of conditions and temp range. 2 - Any electrical issues I've had before are very random in nature. The only thing would be is if there are compounded issues (electrical and solenoid)…

I'll report back if I find anything else, and see what the trans guy can see on his scanner...

 

[Mike L.]

P0776 indicates an off going clutch is not fast enough to not interfere with an oncoming clutch. Tie-up ( 3 clutches on for a milisecond ) when ther cannot be more than 2 clutches on for a clean hand off ( clean shift ). This can be caused by a weak trim solenoid, speed sensor, weak clutch pack, transfer case issue, or voltage problem which causes a trim solenoid issue.

 

[db131994]

I'll rule out weak clutch pack, since it was just rebuilt this summer with upgraded clutch packs. Or at least put it on a lower priority (I hope!!!). Voltage is obviously a concern with the MIL voltage not seeming to be where it's supposed to be... Not sure if that would have any connection to it or not.

What kind of transfer case issues could cause the P0776? I wouldn't have made that connection, but I've been a little concerned about the TC getting a little "sloppy"...

 

[dndj]

P0776 info from GM below

 

[db131994]

Dale,

Thanks for the info. Are there any additional details on the "Test" they are referring too? Also, any thoughts on my testing results of the MIL circuit?

Since the P0700 and P1781 codes shouldn't cause the limp mode, I'm guessing there are multiple issues compounding. P0776 causing the limp mode, and the P0700 and P1781 popping up when the P0776 trips the SES (but I didn't know the P0776 was there). The P0700 and P1781 being caused by the potential voltage issue on the MIL circuit.

 

[db131994]

Talked with the trans guy today. He wants to put a new valve body in it. He said it seems like it must be leaking around one of the solenoids under load causing the issue, or some other issue in the VB. At least that's where he wants to start. He put new solenoids in it before, so those are new, along with the clutch packs in the rebuild. We will see what that does...

I won't be able to get the truck to him until the week of Feb 10th, and we won't pull the trailer again until the 22nd, so it will be a little while before I get any results.

 

[Mike L.]

He's throwing your money at it.

 

[db131994]

He's throwing his money at it. Still under warranty until May.

I redid the C1-25 test with the TCM still plugged in. Same results. Not sure why it wouldn't throw P1781 or P0700 codes all the time.

 

[db131994]

Hey Dale,

Any reason why the MIL circuit (C1-25) would be the opposite of what you posted for the test? No voltage with key off, but voltage with key on? I'm a little lost on that one...

Thanks,