Ford 1997 Aerostar Manual page 22

the tires are changed will also ensure that the
speedometer retains the original factory-set
accuracy.
NOTE: The conversion constant can only be
changed six times once the vehicle
leaves the factory. Your Ford dealership
service personnel can change the
conversion constant.
Some vehicles are equipped with a vehicle speed
(mph/km/h) limiting device that is contained
within the Powertrain Control Module (PCM).
The purpose of this device is to maintain peak
vehicle speed below a specified limit. (Vehicle
speed limits may vary based on engine
displacement.)
If you are experiencing an "engine cut-out"
condition at high speeds, it may be the result of
this limiting device. It is a normal condition and
can be avoided by reducing vehicle/engine
speed.
Speedometer
19