2005 Avalanche Z71 4L60E Stuck in 3rd Gear

[DadpoolTX]

I'm having issues with the transmission staying in 3rd gear. I've seen that it's a limp mode which is typically caused by no power to transmission. I did verify that mine is getting power. When I'm running VCM Scanner it indicates 3rd gear no matter what I manually shift it to. Reverse does act normal, but I have no power forward. Also, no codes except for once when I reved it high to move and got a U0107.

I did add a 3200-3500 stall for the new cam that was installed. Been diagnosing myself and now stuck. Any guidance would be greatly appreciated! THANKS!

[blindsquirrel]

Document ID 1706264.pdf

[DadpoolTX]

It's getting proper voltage and there are no codes.

[blindsquirrel]

This happened after a trans R&R to change a converter? So the big 20-way connector on the side got unplugged then reconnected?

It's real common for the terminals to back out of that connector. The wire can have good +12v on it on the outside, but not be making it through to the internal harness. By some weird fluke it also happens to almost always only happen to that pink +12v wire and rarely one of the others.

Whatever, the behavior and the code is exactly what you get when the trans is not getting power. So even though you swear it's good, dig in and figure out how it is that the wire has power but the trans doesn't.

[TransGo Robert]

Sounds like you are not able to read the codes for some reason. Unplug the transmission and scan it again to see if now it is showing codes. If not, try another scanner. If it does set codes, then reconnect everything, clear the codes and take a short log of all the transmission cannels when putting in OD and taking off gently. Post the log here, and I should be able to help.

[DadpoolTX]

I unplugged the harness and got codes P0740, P0748, P0785, P1810 and P2761. Now VCM Scanner shows that I am always in 1st gear, but doing the exact same thing.

[DadpoolTX]

tranny.hpl

[TransGo Robert]

I unplugged the harness and got codes P0740, P0748, P0785, P1810 and P2761. Now VCM Scanner shows that I am always in 1st gear, but doing the exact same thing.

Ok good so we know the tool can read the codes. Now the log you just posted is useless because it does not have any of the transmission PIDs. You need to take one with all the transmission PIDs so that I can review them all and try to figure out what is causing your issue.

[TransGo Robert]

tranny.hpl

As I mentioned in my other reply this log is not helping for transmission diagnostic since it has only engine data, but I wanted to point out something is wrong on bank number two of your engine. It is not going to cause the 3rd gear only problem you have but wanted to point it out anyway because it will affect lock-up most of the time. It looks like an intake leak on that bank to me, but I am not really all that sharp on engine stuff so it could be something else. Your MAF is also reading much too high at idle if this is a stock 5.3L engine.

[DadpoolTX]

Engine is not stock... Running a Texas Speed BFD cam in it. sorry about the log file...I'll update it now...

[DadpoolTX]

tranny2.hpl

[TransGo Robert]

Engine is not stock... Running a Texas Speed BFD cam in it. sorry about the log file...I'll update it now...

Ok that explains the MAF reading, still something wrong on one bank but that's not related to the issue with the transmsision. It looks like you might have a bad computer. To confirm it, got to the computer and locate the light green wire going to pin 48 of the C2 connector and the Yellow wire with black tracer going to pin 47 of the same C2 connector. Unplug the C2 connector, turn the ignition ON and measure the voltage on both wires. It should be the same as the battery voltage. If it has that, then reconnect the C2 and and now start the engine and rechecks the voltage on both wires. You should now have less than 0.5V on both wires. If you don't have that the computer is bad. If you have that it is in the transmission, there is no AFL oil going to the shift solenoids for some reason. Let me know at that point what the story is on the transmission (new rebuilt, been in there untouched for a long time, etc..)

[DadpoolTX]

I'm not sure of the history of the transmission since I got the truck without an engine. The only thing I did to the transmission is change Solenoid A after getting a P0753 code after first installing engine.

[TransGo Robert]

I'm not sure of the history of the transmission since I got the truck without an engine. The only thing I did to the transmission is change Solenoid A after getting a P0753 code after first installing engine.

Got it. Well let's see what monitoring the two shift solenoid control wires at the computer end reveals and then well have a pretty good idea of where the problem is at.

[DadpoolTX]

No power at PIN 47.

[TransGo Robert]

No power at PIN 47.

Ok so it is a Power issue like everyone thought. No idea why the computer is not doing its job and setting a code for it but fix that and it will work fine.

Does it have power on the other wire with the connector unplugged and the key ON?

[DadpoolTX]

48 does have power with key on.

[TransGo Robert]

Ok so you have an open circuit between pin 47 at the computer and the transmission. Go check it directly at the transmission to see if you have the voltage there or not to know if the open is in the pan or between the transmission and the computer.

[TransGo Robert]

Ok so you have an open circuit between pin 47 at the computer and the transmission. Go check it directly at the transmission to see if you have the voltage there or not to know if the open is in the pan or between the transmission and the computer.

Same color wire at the transmission by the way, it is pin B.

[DadpoolTX]

Ok so you have an open circuit between pin 47 at the computer and the transmission. Go check it directly at the transmission to see if you have the voltage there or not to know if the open is in the pan or between the transmission and the computer.

With C2 unplugged?