I know this is a very old post, but the Anti-lock Brake Module controls the speedometer. The Vehicle Speed Sensor's first stop is the ABS module where the AC sine wave from the variable reluctance output is converted to a digital signal read by numerous modules in the vehicle.
Certain scan tools have the ability to reset the revs/mile in the ABS module as the PCM has nothing to do with it.
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Tuning, PCM flashing, and burning chips for 7.3s since 2008. Repairing all aspects of 7.3L Powerstrokes for 25 years.
Eight 7.3L PSDs in the driveway including a 1994 Crown Vic and 1973 F100/2002 F350. Looking for the next victim.
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