LLY: P0768 Solenoid "D"

[Bustedknuckles]

I'm working on a LLY that goes into limp mode and has this code, the solenoid clicks when commanded with the scan tool and ohms out at 22 ohms from the TCM connector... I was going to pull the VB and check for a sticking valve even though its normally "E" that sticks unless someone has somewhere else to start? Thanks!

 

[Mike L.]

This is an electrical code, not a stuck valve code. Check wires 26, 27, 28, and 31 at the TCM red connector. Work your way down to the internal harness, pressure switch manifold, and solenoid.

 

[Bustedknuckles]

.....

 

[Bustedknuckles]

This is an electrical code, not a stuck valve code. Check wires 26, 27, 28, and 31 at the TCM red connector. Work your way down to the internal harness, pressure switch manifold, and solenoid.

Pin 31 is common 12 volt and 26 27 and 28 are grounded by the TCM to apply or release the solenoids according to my diagram. Since i ohmed it out through the D solenoid from the TCM (pin 27 and 31) and it checked ok does that mean its probably a solenoid failure when it gets hot or should i be load testing and wiggling the wire from yellow/black at the solenoid connector to pin 27 at the TCM connector? Thanks!

 

[Mike L.]

If there was a short at wire 31 you would have more codes as it's common 12V for all the shift solenoids.. If the code appears to be temperature sensitive I would suspect a bad solenoid.
If there is an open circuit or short to ground, the code will come up when the solenoid is commanded off. If there is a short to positive, the code will come up when the solenoid is commanded on. Switch solenoids and see if a different code comes up.

 

[Bustedknuckles]

New solenoid, valve body cleaned and valve bores checked by an allison tech, mike l shift springs, new filter, new fluid and wiring load tested, not just ohmed from the TCM to the solenoid. Still has the same issue, still intermittent. According to freeze frame data the code set at 94% throttle while in 5th gear with 4th gear commanded. Any ideas here?

 

[Bustedknuckles]

Just did it on the 2-3 shift at 43% throttle...

 

[Bustedknuckles]

And now it has only third gear and no reverse. Thats still the only code. Yay.

 

[Mike L.]

Have you tried switching the D solenoid with another one and seen if the code changes?

 

[Bustedknuckles]

Have you tried switching the D solenoid with another one and seen if the code changes?

I did not, i just replaced it and the code stayed the same. That will be my next move.

 

[Mike L.]

You may have a bad TCM.

 

[Bustedknuckles]

You may have a bad TCM.

Swapped TCMS with another truck here. Same issue, really seems to happen after the 4-5 shift whether its up or down. It sticks in 5th and doesn't have reverse. Speed sensors all graph good too fwiw. I guess i might have to throw in the towel and let a local allison guru fix it, i hate to give up though....
Edit: it set's on the 3-4 and 4-5 and 5-4 shift. They are flaring pretty good today, I'm leaning towards an internal problem pretty hard now.

 

[Bustedknuckles]

The customer threw a junkyard transmission in it and its been running perfectly. I guess something was funky with C3. Im tempted to pay the core charge just to tear it down and see whats up.