My Pickup will not shift between 2-3?!

[kyle_druffel]

So i need help and have found one post that actually refrences the problem by bluesmax (What happens is the TCM looks for a "pre defined" torque calculation, off the top of my head it will only reference 776 if im not mistaken. Sometimes if it sees out of range values, or values that catch the TCM off guard it will cause a "defuel/flared" shift. We have even seen them come in doing weird stuff like hanging shifts and downshifting under very light load. The majority of this is ECM tuning via torque tables...).
Can these symptoms take place on a completely stock truck, because this is exactly what my truck is doing and i have done EVERYTHING to try to fix it. To list :


Rebuilt tranny
swapped in tranny out of running pickup
swapped wiring harness
swapped ecm
swapped tcm
changed fuel filter
swapped speed sensors
swapped mass airflow sensor


the symptoms are hanging shifts between 2-3 and then down shifting unless i let off the throttle. when this happens it throws the code P0776. i just got the pickup back from alligator proformance with a 100 percent guarantee that it is not the transmission. Any help would be greatly appreciated.


Thanks kyle

 

[rgullett83]

Alligator couldn't figure it out?

Sent from my GT-I9300 using Tapatalk 2

 

[kyle_druffel]

Well they eliminated it being the transmission by swapping in a tranny out of a running truck which didn't fix the problem. They tried for several months to solve the issue with no luck. I just changed the wiring harness on Wednesday which also didn't solve the problem, so now I'm kinda stumped on what to do. Oh and i forgot to mention the ignition switch was swapped. The only thing i think it could be is the fueling system now, but i don't see how that would effect shifting and cause that code to be thrown.

 

[kyle_druffel]

anyone?

 

[Mike L.]

Did you check voltage at the TCM pins? What was it? Have you monitered the speed sensors for glitches or drop outs? Is there any play in the TC tone wheel? Data stream on the output speed sensor should show that.

 

[BLKLMM]

Damn them alligator trans

 

[kyle_druffel]

Did you check voltage at the TCM pins? What was it? Have you monitered the speed sensors for glitches or drop outs? Is there any play in the TC tone wheel? Data stream on the output speed sensor should show that.

thanks mike. my pickup is currently at the dealership, but i will try to check this stuff tomorrow and get some answers for you.

 

[kyle_druffel]

So mike i finally got some info for you on my pickup, had the dealership check the speed sensor and they said it is acting fine w/ no spikes or drop outs. they also took it apart the tc and inspected the tone wheel which they also said was fine. my pickup is still at the dealership, they have gone through the checklist of possible things it could be when the code p0776 is thrown. so now they are just taking shots in the dark of what else it could be. to check the voltage at the tcm, am i supposed to poke into the wiring harness or can that be check on the computer too? is there any other harnesses that i should check keeping in mind that the trans harness has already been replaced? would it be possible to tune the tcm so it will let the shift happen before it drops a gear? i would like to keep the pickup if it is possble to fix the issue but every day i dont have it and every dollar i put into it makes me think i might be better off to take a giant hit and sell it. Thanks for the Help!

Kyle

 

[duratothemax]

what does the freeze-frame data say when it sets P0776?

 

[kyle_druffel]

selenoid b stuck on

 

[duratothemax]

No, when the TCM sets a code, it should store a "snapshot" of all the parameters/data that was occurring during the second when the code actually sets. Like what the speeds are, etc... Like an airplanes black box.

You'll need a Tech 2 to retrieve that "snapshot" data...but it might give you a better idea of what exactly is going on when the TCM fails diagnostics on P0776.

ben

 

[kyle_druffel]

Oh i did not realize that it did that, i will check on Monday and let you know.

 

[kyle_druffel]

So for that might of been curious to what the problem was, it turned out that the pump inside the tranafer case exploded. Which resulted in the some chunks of the of the tone wheel breaking off. Mike were right about checking the speed sensor graph, the only problem was that the mechanic could npt see it on the graph. Gm actually ended up analyzing the graphs to figure out the problem. It feels good the drive my pickup again after 7 months of ot sitting in the shop!