Hi i gotta 91 3.9 4x4 auto and the truck started having trouble shifting into o/d and i have had problems with the speed sensor before and the truck threw a code 15 so i replaced the speed sensor and reset the codes and it still doesnt shift into o/d and it is still throwing a code 15, i checked for breaks and corrosion in the wiring and i replaced the speed sensor i bought with another one because i thought it could have been a faulty part but still nothing also it throws a code 35 but i dont know if thats related to this issue, any suggestions will help thanks

 

There are several causes for no OD.
1. Speed sensor is bad. (I know you replaced it, I'm just listing it)
2. Bad wiring to the PCM and to the OD switch and the power and ground inputs, (Did you test for correct continuity with a meter?)
3. A bad OD switch.
4. A bad PCM.
5. A bad OD solenoid or bad wiring.
6. A bad coolant temp sensor or wiring.
7. Low or dirty transmission fluid.

 

Ok thanks thats exactly what i was looking for