When I turn the key to the on position the speedo pegs and it clicks of tenths of miles. Must be a sensor? No codes any ideas?

Thanks

 

unplug the sensor on the top of the rear diff and chect to see if it stops

 

I will try that. Thanks

 

I unpluged it and it seemed to fix the problem, drove around all was good, stoped to go and call on getting a new sensor. When I started the truck(sensor still unpluged)the speedo jumped back up and problem started again. I went ahead and changed the sensor anyway. The speedo will drop when it starts then go's back to pegged. HELP!

Thanks