Ok get a load of this... I have a 2001 F-150 4.2 v-6 automatic transmission. Does have a check engine light on for incorrect shift or something. I start the truck up everything come on all gauges all lights, everything is fine. Start driving problem starts. Speedometer doesn't move OD light flashes(constant). Doesn't wanna come out of first gear. I usually shift into second and at different times it surges and my mileage goes to --------- dashes speedometer still doesn't work. But it shifts up and down fine. A little bit of a hard shift but not much. That's if I go from second gear. In Drive it takes first gear way up then its a hard shift and mileage goes out. I have serviced the tranny changed both speed sensors(tranny and rear). ???? And then just to add more salt to the wound occasionally after she gets warm the speedometer works and the mileage kicks back on. Then goes out again. Kinda could be a good thing, because when the mileage is dashes it doesn't tally mileage. I work on big trucks for a living I don't know small trucks that well. but I am trying to learn. Any help or ideas would be greatly appreciated

 

There could be 2 sensors ont he transmission one is the oss it is located in the case the other iss the vss it is located in the extension housing. The oss is a magnetic sensor and the vss has a gear on it.
Alan