96 gmc k1500 limp mode wont scan

[pwesley]

I need help! I have a 96 gmc k1500 truck which I love. On my way home, truck was driving fine. I went to pull in my driveway and it was like it quit pulling. It goes fine in reverse. I shifted to 4hi, still wouldn't pull. Shifted to 4lo and it went forward and I got into my driveway. Check engine light not on tho. When my husband looked at it, my transfer case was full of fluid. Seal leaking (has been for a while, but we keep an eye on it for the most part). Drained case, filled transmission to correct level. Still in limp mode. Hooked scanner, but won't scan. Next morning, truck drove fine while cold. After a couple of minutes, right back into limp mode. Swapped ecm with another one exactly like mine. Nothing changed. Tried different scanner. Still won't scan and Still in limp mode. Pulled pan, no metal in fluid, no bad smell. I don't have alot of money to just start throwing parts at it. Not sure if this matters, but a few nights ago, my dash lights flickered and my heater blend door wouldnt flip over to heat. It finally did tho and my lights are ok now too. I know my truck is old and needs a little tlc, but shes always been dependable and i dont want to get another truck. Money is tight so we do the best we can, when we can. My husband makes sure to keep it serviced and fluids and filters changed regularly. Any help or suggestions would be greatly appreciated.

 

[NickTransmissions]

I need help! I have a 96 gmc k1500 truck which I love. On my way home, truck was driving fine. I went to pull in my driveway and it was like it quit pulling. It goes fine in reverse. I shifted to 4hi, still wouldn't pull. Shifted to 4lo and it went forward and I got into my driveway. Check engine light not on tho. When my husband looked at it, my transfer case was full of fluid. Seal leaking (has been for a while, but we keep an eye on it for the most part). Drained case, filled transmission to correct level. Still in limp mode. Hooked scanner, but won't scan. Next morning, truck drove fine while cold. After a couple of minutes, right back into limp mode. Swapped ecm with another one exactly like mine. Nothing changed. Tried different scanner. Still won't scan and Still in limp mode. Pulled pan, no metal in fluid, no bad smell. I don't have alot of money to just start throwing parts at it. Not sure if this matters, but a few nights ago, my dash lights flickered and my heater blend door wouldnt flip over to heat. It finally did tho and my lights are ok now too. I know my truck is old and needs a little tlc, but shes always been dependable and i dont want to get another truck. Money is tight so we do the best we can, when we can. My husband makes sure to keep it serviced and fluids and filters changed regularly. Any help or suggestions would be greatly appreciated.

Start testing and inspecting the wiring harness that goes to the transmission and the transmission's internal wiring harness, solenoids, speed sensor, etc...Limp mode means you have third gear and reverse, that's it...All other shifts are locked out and all adapts frozen...There's a short somewhere in the system...

 

[pwesley]

Thank you very much. We will start checking everything tonight.

 

[pwesley]

Ok....we replaced the ignition switch, tested all the fuses, and have looked for several days trying to find a bad wire or anything that looks like it could be shorting out. Nothing! Truck drives and shifts fine when you first start it, but once it gets to operating temp, it goes right back into limp mode. Still no CEL light and still won't communicate with scanner. I'm about to pull my hair out! Does anybody have a clue what I could do next? PLEASE HELP!

 

[pwesley]

Ok guys. Here is what we have done. Installed new obd2 port. Finally scans. Got code p1886. Changed a,b,and 3-2 shift selinoids. Cleared codes. Start truck. Drive and goes into limp mode. Shut truck off. Restart, drive and it's fine. Shifts great. Shut truck off. Restart, goes into limp mode. Repeat...
Now when driving and it's not in limp mode, when you let off the gas, it unlocks the torque converter, then relocks when you apply throttle. It used to only unlock when brake was applied. What in the world is going on with my truck??? We go from one problem to another. Not throwing any codes tho. Even with the scanner hooked up while driving and it does this crazy stuff. What do I look for now??