Overdrive no longer works 97 F250
 

I am brand new to the site and was hoping for some direction. I have a "like new" 97 F250 Diesel with 21,000 miles on it that I bought new in 97. For some crazy reason the truck will no longer shift into 4th gear and the light on the shifter remains on regardless pushing to turn off (overdrive on). I have taken to a well respected ASE mechanic but he is too busy to continue. There is no code coming from the PCM indicating any issue. We have replaced the shifter but the old one was in perfect condition no wire or harness issues. The tech says the PCM is going to ground and is likely the suspect but not certain of it. I have read about tail light bulb issues, possible switch or selenoid on the transmission, ground issues etc. Any ideas? This truck has been stored indoors and babied its whole life with moderate pulling weights when used. Thanks for any help. I'm not an expert on this model and have resonable mechanical skills.

Sounds like you have a nice pickup! I'm sure its something minor, like that adjustment on the side of the trans. Right now I can't think of the name of that darn thing, lol. Stupid, is the trans full of fluid?

Thank you for the response. I'm bringing the truck home tomorrow to check the bulbs, the switch and fluid level. Great suggestion!

Sorry, I meant to say "stupid question".

Could there be a short in the wiring for the overdrive switch? Just a thought.

Red

Thanks Red for the response. That was where we first started. Ordered a new shift lever assy and replaced with no change. Also the existing one was perfect with no wire or harness issues. Checked all the fuses as well. The problem started with the truck dropping out of overdrive on occasion, getting worse over time and now the light on all the time. Never had the blinking light with the button and no code from the PCM either.

Even though there isn't very many miles on the trans have you changed the fluid?

No I haven't. Could that cause something like this? It's probably a good idea with 20 years of age.

No, fluid can't cause this. Either the wiring to the OD switch is shorted to ground or the PCM is bad. Those are the ONLY two possibilities.

Thanks Mark. I'm bringing the truck home today and will check all the basics I haven't already looked at. I plan on pulling the PCM and shipping to SAI in Illinois for a rebuild.

Might be worth disconnecting the OD-OFF switch, just to narrow it down.

Thanks for the suggestion and we have tried that already with no luck. I suppose I will bite the bullet and pull the inner fender to get the PCM out and ready to ship.

9 weeks later and my truck is fixed. Turns out the PCM needed to be replaced. Thank you everyone that commented! I appreicate the help!:oval

Thanks for getting back to us, glad you got it going.

Where did you get a pcm? I'm afraid I'm in the same boat.

Truck sounds like its awesome, btw!