I have 2004 GMC Envoy 4.2L I6 4L60 Transmission. Engine has 173k Transmission 92k. I recently had to replace the fuel pump. Car went into Limp Mode. After replacing Fuel pump i test drove and it wouldn't shift into 3rd or 4th unless I let off the gas pedal. Scanned for codes a PO756 shift solenoid B shut off and O2 sensor Bank 1. I dropped the pan and replaced both A & B fluid and filter. Replaced O2 sensor. Test drove for nearly 30 minutes and it got better only would get up to 50 to 60 mph. Transmission shop said needed to be rebuilt. I looked around to buy and came across a used trans with 92k that was rebuilt. It's an 07 trans. bought it for $350 to pull myself. Stuck it in. changed fluid & filter and A & B shift solenoids because i read they are common codes to fail. The trans is doing the same thing. won't go over 65 mph. rpms go to 3800 let off it shifts. no codes. replaced VSS ATPS throttle body and new battery.
Sounds like the rebuilt transmission has the same gremlins your original one did. That is the problem with rebuilt transmissions: you never know who rebuilt it, how well it was done, or why it was rebuilt.
Honestly I'd be looking for another vehicle.
1st question: Did you buy an OEM fuel pump? This is a must.
#2
the transmission uses a few engine parameters to shifting operation. I don't know them all off the top of my head, but they include things like engine load, accel pedal position, manifold pressure etc.
So the electronics need to be working correctly for the tranny to shift.
I had a 4l60 and was having symptoms similar to yours, and it turned out I had bad ignition timing and a dirty fuel filter
Yes it was an OEM fuel pump. Pretty expensive too. New fuel filter. Double checked to make sure it was installed correctly. I haven't checked the the fuel pressure or replaced the map sensor.
It's kind of interesting that the ECU and TCM uses RPMs and Throttle Position Sensor input values (among other sensor values like MAP and vehicle speed from the VSS ) to adjust pressure and establish shift points and you can get your transmission to shift by decreasing your TPS% angle by letting your foot off the accelerator pedal at certain RPMs and changing the TPS angle % being reported.
Have you performed the transmission control module reset?
The procedure calls for moving the TPS to full open by holding the accelerator to the floor, waiting a prescribed period of time, and then completely taking your foot off the pedal which seems to imply that the TCM is learning what angle % a particular TPS is reporting when the pedal is fully depressed (Wide Open Throttle ((WOT)) and fully closed.
Might be worth a try to perform the GM 4l60E TCM reset procedure.
....just putting it out there
Thanks for the recommendation. Tried that and it didn't help. Turns out the catalytic converter was stopped up. It was allowing just enough exhaust to pass through. The motor never once showed signs of a cat problem. Computer never gave a code for it just a faulty signal code for an O2 sensor. Thanks everyone for all the great info. I now am an official GMC Envoy specialist LoL!
Hard to believe 2 transmissions with the same problem. Any ideas on what could cause this if you know that the 2nd transmission was in good operation before installing it?
This website should answer your questions: https://twincharlotte.com/30-common-4l60e-transmission-problems-repair-charlotte-nc/
Yea I've read that site. That's why I've replaced the few things mentioned in their list of problems. Unfortunately no success. I still have to replace the harness. If that doesn't work then I'll have no choice but to junk it. I'll post again if I resolve the problem.
mine just went out those transmission are absolutely garbage junk the piece of crap and get something else
I would but I've already sunk too much money into it