I'll try to keep this short. With truck driving at any speed my overdrive light will cancel turning my overdrive off. It will also cancel sitting parked with KOEO or KOER. The light will turn on and off 20 times in one minute or will be good for 1 hour. While driving the truck it shift good into 4th gear but then cancels and shifts to 3rd. Light goes off, shifts back to 4th.

The on/off of the light is NOT a blink code. Scanned the truck and has no codes, dissconnect the connector in the steering column for the overdrive off switch, take it for a drive and the truck will still cycle in and out of overdrive; still having the same shift feel as always.

So this is the trouble shooting I've done so far.

-17 fuse powers switch, of corse that is good.
-29 tan/wht wire at ECM is the switch 12 volt signal
-79 wht/lgn wire at ecm signal wire to turn on the overdrive cancel light on or off
-Line pressure is good
-while driving all the shift seliniods are working properly
-temps still at 170 degrees
-removed the filter and cut open, everything was good.
-All battery connections good and ecm ground supply is clean.

Mechancialy my transmission looks good.

I cut the 29 wire to the ecm to confirm there is no short in the dash turning the overdrive off but it still shuts off as I can see the cancel light still comes on.

I checked the wiring harness to the seliniod pack and that is good, harness to the range sensor is good.

Performed a datastream check while driving and all the seliniods are functioning in each gear properlly as per service manual.

I Scanned switch out puts and keep in mind I cut the overdrive 12 volts signal feed at pin 29 at the ECM, the ECM is still switching on and off according to the scanner in the KOEO state.

Sometimes when I cycle my ignition key on, the overdrive is already canceled.

So I'm suspecting that my ECM is faulty but woundering if there is any possibility that something is telling my ECM that overdrive needs to be off like a faulty TPS/seliniod/line pressure signal from inside that transmission that could back feed to the ecm even though, it passed all my tests.

Just checking to see if anyone has come accross anything goofy like this that has another check for me to do.

 

The only way that the PCM turns off the OD is when it sees 12V on the signal line coming into the PCM. There could be something wrong inside the PCM that makes it see 12V on that pin.

There is nothing else that will make the PCM turn on the light and turn off the PCM.

 

Just for future searches, the ecm/pcm was the problem, replaced it and everything is working good now.