My speedometer is lying to me. I can be parked and at an idle and it will jump up and peg itself telling me I am going over 100 mph. Now I am not dumb. I just look out the window and verify that in fact I am still sitting still in the driveway! Sometimes it tries to tell me I'm going over 100 sometimes 10 or anywhere in-between all while sitting still. This can happen while I'm driving too. It seems to be more of an issue during cold weather but can happen even during warm weather. Sometimes I can be sitting at an idle and rev the engine just a little and get the speedo to jump. I have on a few times had the tachometer jump a few times too, but never on its own and only once or twice. Has anyone else had this issue? If so how did you fix it. Any suggestions on where to start trouble shooting?

 

Take a look at the wires (twisted pair) that go to the speed sensor on the rear differential, they are probably beat up from driving gravel roads.

 

Busboy-ok I'll start there. I do drive on a lot of gravel/dirt roads here in NH so it seems like good advice on where to start!

 

Ok-checked the wires coming out of the rear differential. They were very dirty but otherwise appeared ok. Ideas from anyone else?

 

I had the same problem with a '01 Dakota. I removed the sensor from the top of the differential and cleaned it. The problem got a little better, but didn't resolve it. Then I replaced the sender, and that fixed it.

 

I agree that the sensor would be the first thing to try and will probably fix the problem.

 

Ok, so I finally replaced the speed sensor AND.....nothing changed. Speedo stills jumps all over the place. I've noticed that it seems to be worse during wet weather or cold weather. Sometimes in the winter after running the truck for a while the issues goes away for a while....anymore ideas anyone???

 

Best bet is to find someone that can read ecu data, have them watch speed input from the sensor. If thats stable I would be suspect at the cluster or ecu output signal. If the ecu is reading the same jumpy signal from the sensor then I would start there.