Swagger

My overdrive only works when the truck is cold, and only for about 5 minutes after a cold start.

I've checked the TPS and it seems to be functioning normally. I've adjusted up and down to see if there was any difference. Still no overdrive.

I think the problem is temperature related, however I don't think that engine or transmission is operating outside of normal temp ranges...so I think something must be failing.

I am fairly new to mechanics so this is a bit of a mystery to me. I have checked the stickies...I wasn't able to find the gold nugget in there that would help me fix my problem.

What is the diagnosis?

Tuckerdee

There's a temp sensor on the tranny fluid cooler line, right after the fluid exits the transmission. If fluid temp is over a certain temp (I forget what it is, but it's high, something like 315*) it cuts the O/D out. Probably that sensor is going ker-flunky on you. I'm not sure if it's normally open or normally closed circuit. You could try just unplugging the connector and see if it works.

wannadiesel

It's an NC switch, you have to jumper it.

I'd just check it for continuity with the truck at normal operating temp.

If it passes, try hot wiring the OD solenoid by grounding the wire that ISN'T blue in the solenoid plug. If you can't get OD that way, and the blue wire has power with the key on, the trouble is inside the trans. Check continuity on the OD solenoid with the trans warm to rule out a bad solenoid before you decide it needs a trans rebuild.