alright fellas... i just bought a 06 6.0 with 79,000 on the clock. my speedo is all over the place. one day it will not come off zero, the next it will seem to read ok and then just stick at a certain speed at a stop and then climb from its last position. its about 15* here. ive read a couple of different scenarios. one is that there is a coating or something of that nature that causes the needle to stick esp when it is really cold. and also the wheel sensors. anybody shed some light on this?

 

Check the Speed sensor which is located on top of the rear axle houseing. It could be bad or just needs to be cleaned off. had this happen to my truck ( 07 f350 with the 6.0). If it dont fix it after cleaning it off its probably bad. They are about $100 at Ford dealerships.

I have also ran into another problem with the speed-o acting up. The wiring harness thats on the drivers side by the fuse box in the engine compartment sometimes comes lose ( clips together) I found one that was a little loose and jsut clipped it back together and have had no problems since. BUt when that happened it also shut off my Odometer/ Trip meter and my turbo boost would not work.