2008 Ford Ranger

You guys know if there’s a way to calibrate the speedometer? My truck is off about 3-4 mph. Tire size on truck is what is shown on door jam….thanks

 

At what speed is a 3-4 MPH off?
If above 60 MPH that's within spec

You need to use a laptop/tablet hooked to OBD2 port under steering column with Ford software

I think Forscan software can do it
Check at the Forscan forum

2001-2011 Rangers use the Engine computer(PCM) to calibrate speedometer, AC Pulse speed signal comes from OSS sensor on transmission
You need the laptop/software to change the PCMs calculation numbers
It uses Revolutions per mile, revs/mile, not tire diameter
A 28" diameter tire does 747 revs/mile, as an example
Not sure if you can just enter any number, the numbers are usually pre-set, you select it from a list, and that list of revs/mile is based on 1/2" differences between tires
Like this list: https://www.mickeythompsontires.com/...per-mile-chart

Which is where the 3-4MPH error comes from

Tire inflation matters as well, lower tire air pressure, in essence, reduces the diameter of the tire, a 28" tire becomes a 27.75" tire or 27.5" so lower revs/mile
Higher tire pressure does the opposite

 

Thanks for the reply….yes it’s 3-4 mph off through all speeds by my 2 separate GPS apps on my phone. Ford dealership told me Ford no longer supports the software to change it. It’s just annoying to have it not read correctly. Thanks for the info and I’ll check out Forscan you mention….

 

Forscan is like an OBD2 reader on steroids, so can read and clear codes but can do a whole lot more

 

That's not a calibration issue, that's a speedometer head issue, you won't be able to correct that.

A calibration issue would be off by a percentage, a 10% off would be off by 1mph for every 10mph actual speed.

10mph off by 1mph
20mph off by 2mph
30mph off by 3mph
Those can be corrected.

 

Thanks 👍🏻