F 350 4WD Pickup V8-351 5.8L VIN H EFI (1997)
Speedometer Module: Description and Operation
Programmable Speedometer/Odometer Module (PSOM)
Programmable Speedometer/Odometer Module (PSOM)
The Programmable Speedometer/Odometer Module includes the Speedometer, the Odometer, and the Trip Odometer, all of which are
electronically controlled by a programmable integrated microprocessor. The microprocessor receives a speed signal input from the Differential
Speed Sensor (DSS), and uses a programmed conversion constant to convert the signal to the standard 8000 pulses per mile speed signal output.
The Programmable Speedometer/Odometer Module is serviceable only as a unit.
The electric analog speedometer receives it's input from the anti-lock brake sensor. The liquid crystal display (LCD) odometer is a combination
trip odometer and total odometer. The total odometer is normally displayed. To See the trip odometer, press and release the SELECT button on the
upper right side of the speedometer. To zero out the trip odometer, press and release the RESET button on the upper left side of the speedometer
while the trip odometer is displayed. If the trip odometer is displayed, press and release the SELECT button to return the display to the total
odometer value. The speedometer, containing the trip odometer and total mileage odometer, is serviceable only as a unit.
The speedometer is also used to provide Speed signal for correct operation of the vehicle's EEC module and speed control (if so equipped).
Because of this, it is VERY IMPORTANT to change the speedometer's internal conversion constant if the size of tires on the vehicle is changed.
Changing the conversion constant to the proper value when the tires are changed will also make sure that the speedometer retains the original
factory-set accuracy.
