I just got a 2012 Ford Fiesta S (5-speed manual) a couple days ago. It's running great, but I noticed the speedometer reads about 3 MPH too high at around 55 MPH when comparing to the speed on my phone/GPS. The speed reported by my phone exactly matched the speedometer on my old Cavalier, so I'm assuming the Fiesta is a bit off.
The Fiesta reads 0 MPH while stopped, so the zero point is correct.
Is there some user-servicable way to adjust the calibration? If it involves buying a $100-200 tool to connect to the OBD-II port, it probably wouldn't be too hard to talk me into that, since I'm sure I'd find other useful things to do with it. I have an Actron scanner, but I don't believe it's capable of changing any ECM parameters, apart from clearing trouble codes.
The tires are 185/60R15, which matches the label inside the door.
I pulled up the digital speedometer (which is hidden in the instrument panel test mode), and also hooked up the Actron, and those two readings agreed with each other, not surprisingly. Both showed within 1 MPH of the speed displayed on my phone, whereas the analog needle was another 2 - 3 MPH higher than that. So it seems like it's just a needle issue, meaning my odometer and MPG calculations won't be way off at least.
The needle's zero point is correct, though, so I don't think it's just a matter of ripping the dash apart and repositioning it on the stepper. Is there any way to adjust the scaling of the needle's movement?