No Overdrive

[moose55]

I have a 93 GMC 3500 2wd Dualy. The trans stopped shifting into overdrive, for a while I could cycle the ignition switch a couple of times and it would shift into over drive, but as soon as I would let of the accelerator it would fall out of OD and not go back. I have tried to pull codes using the latest scanner from Snap-On and all it said was that it couldn't comunicate because there wasn't a engine ECM. I talked to a local trans parts house and i tried the only two things they could think of. I replaced shift silinoids A&B, the internal and external wiring harnesses and nothing has changed. I have also tried adjusting the throttle position sensor.

PLEASE HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[Robyn]

There is an ECM for the tranny only on 92 and 93 diesels.
The snapon scanner may not be set to pick it up though.
If its not going into OD there almost has to be an electronic trail left behind.
Are you sure its the OD your not getting or is it the Lockup ?? when its gone as far as it will go try pulling the shifter down to 3 and see what happens. If it drops down a gear the OD is fine and its the TCC thats not working.
If this be the case the switch on the brake pedal that unlocks the TCC when the brakes are applied may not be working properly. You may very well have a TPS thats bad, the TPS is located on the IP and sends a signal to the ECM as to where the throttle is. If the TPS goes away it can cause a variety of weird crap to happen too such as what you are seeing.
Let us know
Robyn

[moose55]

It isn't the converter lockup. If you put it in third it has the same RPM as OD. I tried to adjust the tps sensor and the truck would hardly move. When I get to town again I will try my friends new trans software on his scaner.

Thanks for your help!

[moose55]

I finaly pinpointed the problem, a bad conection in the plug for the TPS sensor.