I have a 92 gm 4x4 with 4l80e trans. i have lost od with no engine light. checked all hookups and still connected. when it acts up i have turned off ignition while moving then restarted engine in neutral, and truck would sometimes go ahead and shift into odrive. may not have any correlation but throwing everything out there. changed ignition switch on column worked fine 2 weeks now wont go into od at all. also seems to shift into 2 hard when not shifting to od. any help would be great thanks.

 

how many miles are on the tranny?.......sounds like you may have an application servo motor going out....when was the fluid changed last? does it have an external cooler on it? sorry to say but it sounds like you are in line for a rebuild

 

bought truck used so i dont know fluid smells good and red but not like it is new, and other than sparatic prob works fine even pulling a 28 foot trailer loaded in third or overdrive.

 

sounds like a physical problem and not an electrical one.........dropping the pan might tell you more than you want to know....but I would suggest doing it...and while you are there you should change the filter too

 

you wont get any dummy lights if your tranny is having problems.sounds lik the 3-4 clutch paks are worn.when the linning wears off the clutch pak they wont grab and hold they just try to grab(slipping).sounds like a rebuild.where do you live,my dad specializes in gm trannys and has many rebuilt with conveters on hand.you might be able to hook up and help you.

 

put on scanner but not familiar with findings checked against a friends truck and found scanner diff to be no tcc duty% and the good truck would turn on sol a, friends truck would energize sol a then it would shift to od mine never turns on that sol a or gives ANY tcc Duty % again truck shifts great in all other gears with no skips shutters or slippage

 

at this point it looks like you have 2 options........1 change the OD solinoid and hope that it is the only thing wrong...and when you go to do that you will know if you need to do option 2 before you ever install the solinoid....2 rebuild it.....I still think a pan drop is in order here to help diag the issue a little farther

 

took to local shop that had a different scanner and when we drove it they could manually shift the truck into od and worked fine so wiring harness is good it said the throttle pos sensor was bad yet replaced and still no shift any suggestion would be great thanks

 

there are several things to look at.........the VSS gives input for trans shifting....so does the tps.....does your tps have a good ref voltage? as far as manually shifting into OD im pretty sure that is not possible...from what I remember OD is ALL electrical (as far as application goes) its not like 1-3 ...which is done by a "valve" in the valve body that is hooked directly to the shifter and allows fluid to flow through diffrent passages to obtain the diffrent "gears"..........check the VSS and the TPS ref voltage and let us know....if I remember right ref voltage SHOULD???? be 5volts

 

My truck is doing the same thing. I have changed tranny fluid and just changed the TPS. It drives perferct, shifting into OD until it is good and warmed up. Once it is warmed up it pops the check engine light and will not shift into OD. Last time I had it scanned it said "TP low voltage" Any ideas?