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Mitsubishi Lancer SRS Light Stays On

Q. Dear sir, I have a 1992 Ford F350 1-ton with a 7.3 liter diesel engine. It has an automatic transmission with 202,000 miles on it. It had ABS brakes on it. I have a problem with the speedometer. When first started and drove it will not work, then it will start bouncing and finally level out about at the right speed, with an occasional jumping up and down of about 20 mph.

Mitsubishi Lancer SRS Light Stays On

I changed out the speedometer with one from the wrecking yard but same problem. Can't find a sensor on the transmission, but I do know the RABS sensor if unplugged will cause the speedometer not to work. I have had an ABS warning light on for about two years though. This problem is about three months old.

Does the RABS sensor go to the speedometer also or through the ABS computer or is there another speed sensor?

Thanks,
Harold

A. The Programmable Speedometer/Odometer Module (PSOM) 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 PSOM 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.

Additional Information provided courtesy of AllDATA

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