We used to have to replace the gear on the speedometer drive unit with one with the number of teeth specified for the tire size and axle ratio. Since about the late '80s or early '90s those numbers are selected from a list on a scanner and entered into the Body Computer or Engine Computer. The programming has to be changed when different size tires are installed.
April, 4, 2014 AT 6:25 PM
Yeah, it could be the penion gear or tire size? This cheap to fix?
April, 5, 2014 AT 7:45 PM
Pinion gears are cheap, especially if you can find the right used one in a salvage yard. Reprogramming is real fast, but Ford dealers usually charge plenty for the service. Many independent shops have aftermarkert scanners that may be able to do it too.