CTD2001

My buddy has a 93 auto and is having troubles with his overdrive engaging. When he first drives the truck he has no problems with the overdrive engaging, but after the truck warms up, it will no long engage in overdrive. The overdrive on/off switch does not always function properly. Some times the light on the button will come on and go off with the pushing of the button, but other times it will do nothing. I did some searching and read that there is an overdrive selonid inside the tranny that may become loose. Any help that you guys can shed on the problem would be great, thanks

CTD2001

anyone have any ideas?? He called me tonight and said the truck was shiffting fine, I told him to drive around for a little while and let it warm up, sure enough, it stopped shifting into overdrive.

JD730

Sounds like a possible Throttle Position Sensor problem.

The OD button light on/off not working right sounds like a PCM problem, but they usually work when they're warmed up, the wait to start light will usually flash rapidly when a PCM is acting up, not always, but I've had 2 different ones do it.

Don't forget about the temp switch in the hot line, supposed to open at 260*F or something like that.

Did you do a search yet? There is some threads in here about the same thing recently. Also check the sticky.

I think a switch to bypass the PCM is in order to troubleshoot this problem. There's a 2 wire plug above the shifter linkage, 1 wire is fed 12V when the key is on, the other is grounded to activate the OD solenoid. I can't remember the colors, but the wire that gets grounded is the one you want to splice into and run into the cab so a switch can be used to ground the solenoid. If OD works when the switch is on then the problem is on the PCM/TPS side of things, if it won't go into OD when its up to temp then its probable in solenoid.

wannadiesel

Don't ground the blue wire.

CTD2001

Thanks for the reply, i found the "sticky" thread, lots of good info there, i will have to do some reading.
I also found this thread, do you guys think that this solution may work??
https://www.dieseltruckresource.com/...threadid=74673
I dont think it is a TPS problem because the truck shifts fine before it gets warmed up. Also the OD switch functions properly when you first drive the truck, but stops working when it gets warmed up. The Wait to start light does not flicker or anything like that.
Thanks

wannadiesel

Can't hurt to check.

ChrisLib

Sounds like it could be it, like Wanna said, can`t hurt to check and if nothing he`ll get to service the unit and adj the bands....wow, it`s been two years already, the OD`s worked flawlessly since....ka-nok wood.