I have a low mileage F250 4x4, 460, with 57k miles. Truck was owned by retired couple who brought it to Oregon from California in 1999, with only @50k, so it has sat most of the recent years. Have been sorting things out, servicing the transmission, etc.

The truck does not shift into overdrive, but the overdrive off button on the dash lights up when you depress it.

Does anyone know if the truck will throw a code to help diagnose the problem, or is it a known problem?

 

It depends if the code is electrical, or mechanical


Electrical will show up, mechanical, no
If there is a code, it will probably say something about overheating, etc

That is a pre 95 transmission with all the upgrades, so there are a lot of known problems, and with it being low miles, I'm sure they aren't sorted out

I saw where you power flushed, that's a good start
What color was the fluid before you did that?

Another issue is the wire harness on the passenger side behind the heat shield beside the cat
The plug deteriorates over time
be careful ordering a new one if this is the issue with yours, the 95 updated one is a different shape

I guess the best start, is codes for now.

 

Thank you. Fluid was ok, but I did not power flush. Have a friend who is a long time transmission expert, who told me how to drain transmission, converter, then fill and take the return line loose, then put a piece of hose on it. Then run it, and stop when the old fluid is gone, and you see the new stuff. That way you get a complete change. Will check codes in the next few days.

 

So you didn't change the filter?
Dropping thr pan to do that shows if pieces are presant. It also shows how much clutch sludge is in there
https://www.fordtruckzone.com/threads/e4od-service-on-a-1990-f-250.660000/

 

Yes, did the pan and filter. It looked good in there, so will hope it's the mlps aka neutral safety switch.

 

Though I'm not familiar with this transmission in a 91 model gas truck, they also used this transmission in the 7.3 PSD trucks from 94 to 97. Those, I am familiar with. A faulty brake switch could affect it, as well as a burned out brake light. That includes the 3rd brake like if it has one on the cab. My 97 had the speed sensor in the differential. Sometimes it can be bad, even though the speedometer still works. Dustybumpers is right though, check for codes, then take it from there. Understand, I'm familiar with the later models of this transmission. I could be way off base with your truck though. I will say though, if you got a 91 with that low miles, you should have a great truck when all the bugs are worked out!

 

Same bells and whistles on early model gassers John.......
Only Speedo is still a cable, ans 2nd speed sensor on transmission

 

So the codes I found were 74 and 77. I did not do the wot test, foot to the floor, since my info said it was not part of the procedure for my truck.

Since the test, I replaced the brake light switch, and the mlps or neutral safety switch, along with the tail light bulbs. Still no overdrive.

 

I was told of a plug that deteriorates behind a shield, next to the cat. Will try to check that today.