i just recently purchased a 96 3500 dually. the engine runs great but im having problems with the tranny. The shifts seem fine until you get to overdrive. the tranny will constantly kick itself back into drive even with the cruise on but if you just push the throttle it will go back into OD. if you are constantly accelerating it stays in. I seen in another post someone said something about the cooling system sensor having something to do with it. not sure why that would be but i do have a low coolant light on and the coolant is fine. My brother is a mechanic but i dont want to bother him with it too much because he is busy but we took it for a ride the other night and got a apps code pop up. it seemed to make sence so i took the pedal out of a parts truck thinking i had it figured out and it was the same thing. if we drove it with his scanner on it which i think was called a tech 2 if i remember correctly he can take over transmission function and shift it of the computer and it stays in OD no problem which has me leaning away from mechanical and more twords electrical. Does anyone have any ideas what it could be. The truck is almost impossible to drive on the highway.

thanks

 

cooling sensor which on the the T-Stat housing talk to computer one way see f that the problem is unplug it and if the idle goes into high idle then it good

check all the ground they play big part with these motors check trans plugs and mke sure they are clean and conntcet good

 

Thanks for the reply i will try that. i also have a code for boost pressure too high. it is at 14psi on the engine scanner at an idle with the wastgate at 65%. any ideas. i replace the boost sensor that is on the intake with one from a parts truck and no change . wastgate seems to be moving properly.

thanks

Just tried the coolant sensor and the truck did idle up.

 

ok i think the over boost problem is the solenoid but the over drive problem is really pissing me off. it will go into overdrive but as soon as you let of to try to maintain a speed it drops back to drive or maybe its third it will also jerk and the rpms bounce around. are there any other sensors that could cause this?. Speed sensor maybe

thanks

 

My 97 does the exact same issue and i can agree it gets REALLY f*@king annoying especially when your trying to save fuel / get good mileage, i don't have a scanner worth a damn it'll give me coolant temp, intake temp, and that's about it. I dont have the money to take it to a trans shop either.
Not sure if it's kicking back to third or unlocking the converter, on mine if I drop the selector back to third when its acting up it'll go up another 150-200 RPM, and when i throw it back up to OD it seems to lock back up and hold even on coast, I've been starting to think maybe a pump problem or sticking valve. Might have to break down and take it to a shop so we can figure this damn thing out

 

im in the process of changing my transmission now. went out one morning and it didnt want to back up and then started getting to the point of barely moving. i have a spare so its going in.