I have a 2001 Dodge Grand Caravan Sport. For the past year or so, the speedometer would go crazy or drop below the 0mph line. I reset it by holding down the odometer button. Worked like a charm. In August, the transmission started acting up, and again the speedomoter went crazy. I brought it to my mechanic who put in new speed sensors. That did not fix the problem. He put in a transmission, a TCM, checked all connections, even replaced the speedometer itself, and the car still will not shift correctly as the speedometer still goes crazy. He has tested all parts to be sure they are good. The diagnostic computer still points to the input and output speed sensors, but he has replaced them twice. He has gone over 1/2 the wiring in the engine looking for a crack causing a short. No luck. He has had the van for 2 weeks now and is about to give up. Thankfully he is an honest guy and is not charging me anything despite the many hours and parts he has put in. I know there is still life in this car, but I do not want to bring it to a dealer and get charged for many hours of diagnostics, repeating what has already been done. Anyone out there have any thoughts on what might be causing this??? Thanks in advance!!

 

Looks like your mech has touched all the bases and then some. Looking at a wiring diagram the sensor signal goes to the TCM then on to the PCM then out the PCI data bus to the cluster. I've never read f a PCM causing this but you might consider it. Beyond that you might consider changing the wire harness involved or just the wires involved preferably by pinning then in or if need be splicing.

Did he use OEM sensors?

 

Not sure if he used OEM sensors - I will ask. Thanks for other wiring suggestions. I'll run them by him. There has GOT to be a solution to this!!!!