What happened to my overdrive?

[R3D'91]

my stock 91 seems to have lost the ability to shift into overdrive, what is the best way to troubleshoot this? I have already verified that the linkage is adjusted properly.

 

[MrShorty]

I know I've posted specifics a few times before. I think the best thing to do first is to determine if the no od is in the EEC-IV part of the system or not. If it is, then you can fix what you find, if not, then the problem is hydraulic/mechanical and will require at least some disassembly of the transmission.

Start by pulling codes from the computer (see my notes on pulling EEC-IV codes). Resolve any codes that come up. Once you're getting all pass codes, and the problem is still there, then test the 3-4 shift solenoid circuit. It's a pretty basic DC circuit (computer acts as a ground side switch) and isn't too difficult to test.

 

[R3D'91]

MrShorty, thanks for the response, I have pulled codes on this vehicle before using the needle sweep technique on my multimeter, is this the method your notes refer too? and where can I find your previous posts regarding this?

 

[mgmgmg]

I had the same problem with my 94 Ltd. It was the mass air sensor..... of course i had a code reader to solve the problem.

 

[Jack Norwood]

Have you had the battery disconnected? If you have you will have to get it out on the road and get speed of about 65MPH for it to reset the computor. My 93 did this when I changed the battery. Just a thought. JNor.