Automatic transmission won't shift to overdrive

[Hittinger]

Truck is a '96 with 80,000 mi. The automatic trans. will not shift into high gear or overdrive. I checked the throttle position sensor with a voltmeter and it was working within specs. The trans. fluid was completely flushed,new filter,Mag-Hytec DD pan,with Amsoil atf fluid. Trans fluid was checked while engine/transmission was hot with engine running in neutral, fluid level looked fine. The transmission fluid has been changed ever 24,000 mi. with a new filter and always looked clean in the pan. I have run out of ideas to check. Does anyone know of anything to look for. This symptom just started occurring several days ago. Any help appreciated. Thank You.





One Hot Desert Dawg,



Keith

 

[Strick-9]

You don't mention any dash warning lights, so I'll assume you have none.



The PCM should lockout 4th gear until the transmission temp and engine coolant temps are above a certain level.



It COULD be a failed temperature sender or an unplugged wiring harness.



I wish I could help more.



-Chris

 

[Joe G.]

In addition to what Chris suggests, you might try adjusting the kick down cable. If none of this works you might try some pressure tests. If you don't have a service manual NOW is the time to get one! The pressure test for the governor should show about the same PSI as the speedo shows MPH. It could be sticking. It's kind of hard to diagnose something like this, but you don't want to just throw parts at it until it goes away.

 

[Bill Kondolay]

It is possible you have a transducer or governor solenoid problem since you lost both od and 3rd gear.



It is also possible that the transmission is in limp mode, which can be caused by a lot of different reasons not necessarily caused by the transmission.



It is best to have your vehicle scanned to see if there are any codes.



If you are looking for a used transducer or governor solenod i am sure i have a few kicking around that you can have, you would have to just pay for the shipping.

 

[tmarti96]

used parts laying around

Good for you, Bill K. Not many vendors will offer to give away parts, used or new. You are appreciated.

 

[Dieselnerd]

This is coming out of left field but check your transmission relay. It's in the little box just to the rear of your driver's side battery. If it fails to pick, your transmission will not go into OD and hangs in one gear and will not lock up. Pull the relay and install a jumper across the 2 contacts closest to the battery. You will see that the relay has 3 prongs on the side closest to the firewall and 2 prongs on the side closest to the battery. You can leave the relay out with the contacts jumpered with no problem. The relay is not needed for proper operation when jumpered. It provides 12 volts to some transmission circuits. I had a similar problem not long ago with symptoms like you describe caused by failure of the relay to operate. (my own fault but that's another story)

 

[Extreme1]

You can do a "scan" yourself!

As long as it isn't an OBD II (don't remember what year that started), you can do it by turning the "ignition" switch to run and off 3 times quickly. Leave it in the on position the 3rd time. The check engine light will flash a number of times. These correspond to 2 digit codes and if you can post them, we might be able to help.