I have a 99 Durango and the Speedo isn't working. Mechanic Changed the speed sensor , but that didn't work. Any ideas ?

 

Which sensor did he change? On yours, I do believe the PCM gets it's clue about vehicle speed from the sensor on the rear diff.

 

There is a sensor in the trans and one on the diff.

 

Sensor in the trans is the Output Speed sensor. PCM doesn't use that one for vehicle speed.

 

I'm pretty sure I've read in the FSM before that it can be used as a backup for that function.

 

I suppose, the question here becomes, is this a sensor problem, or a gauge problem? If the ABS and Brake lites are also on, then it's likely a sensor problem. If they are not, that implies the PCM is actually seeing a vehicle speed signal, and it's the gauge that is the issue.

 

Throwing my $.02 in, on my newly acquired 2000 Durango, I replaced both the sensors on the rear diff and transmission and still had no spedo...all because of a blow fuse. It also took the replacement of the ABS control module to get my ABS and Brake light off. Wish I would have checked the fuse earlier...would have saved a days frustration lol

 

IIRC the PCM uses BOTH sensors for speedo control, there is a handoff at some speed (iirc 25mph) where if one sensor is out you will have no speed below that and then the speedo will jump up to your speed, the other sensor can be used for the whole speed range if the handoff doesnt happen properly (is my understanding).

 

[Another 'drive-by' first post? Wish the OP came back to read all these great answers.]