automatic trans

i have 1990 Grand Caravan trans will not go into over drive,fliud is full ,so i know that not it.so is there a speed senor that is bad . There are two ,a output speed senor and a input turbine speed

Take it to a good local transmission shop. They usually scan it in two minutes by a connector right next to your fuse box under your dash. They usually don't charge for this. Best of luck.

so did you get it fixed?