Hi
I have a 2003 Expedition with stock tires . I noticed yesterday that my speedometer was reading 70MPH while the GPS is showing 75MPH. I later dropped the speed to 60MPH and the GPS showed 64-65 MPH. Could the previous owner had changed the gearing down from the 3.7 stock or its just electronics that can be re calibrated?

Also my the driver side door lock is erratic , it is currently not responding to the remote or the button to lock and unlock. but it switches back and forth. could that be a loose connection inside the door?
Thanks

 

I would trust the computer over the gps guided speedo. Ive seen that before. I wouldn't rely on the gps. Some are more reliable than others. Next time you drive by one of those radar speed signs, see if you could tell which ones closer.
As for the switch, sounds like something more mechanical. best bet is to pop the door panel and take a closer look. however, could be like you say, loose connection or switch itself.. You gotta open things up and start investigating. hard to say really..

 

For the MPH, are the correct tires sizes on the truck?

For the door lock, it could be a bad lock/unlock relay.

 

The truck has the standard tire size 265/70 r17. I now used 2 different GPS unites and did the old stopwatch on the mile marker calculation and they all still show that the speedo is about 5 MPH slower than actual speed.

I would appreciate any ideas for fixing this problem.

As for the door lock, where is the lock/unlock relay located? is it a relay for the driver door only or for all doors?
Thanks

 

There is a driver's door unlock only relay built into the vehicle security module.

 

You're stuck bringing it in to be calibrated.

 

That or run a calibrator box inline with the speed sensor but you are better off taking out in. Just fyi, most speedos are off right from the factory. Door lock... relay or loose wire or the actuator itself.