Cherokee 4WD L6-242 4.0L VIN S MFI (1992)
Wheel Speed Sensor: Description and Operation
One wheel speed sensor (WSS) is located at each wheel and sends a small AC signal to the control module (CAB). This voltage is generated by
magnetic induction when a toothed sensor ring (tone wheel) passes by a stationary magnetic sensor (wheel speed sensor). The CAB converts the AC
signals into digital signals for each wheel.
The front wheel sensor is attached to a boss in the steering knuckle. The tone wheel is an integral part of the front axle shaft. The rear speed sensor is
mounted in the caliper adapter plate (rear disc only) and the rear tone wheel is an integral part of the rear rotor hub. The front wheel speed sensor air gap
is NOT adjustable. The correct front wheel speed sensor air gap is from 0.40mm to 1.3mm. Preferred rear sensor air gap for drum brake systems is 1.1
mm. Acceptable air gap range is 0.92mm to 1.275mm. For rear disc brake systems, the preferred rear sensor air gap is 1.2mm. Acceptable air gap range
is 0.95mm to 1.45mm. All wheel speed sensors have a resistance between 900 and 1300 ohms.
Correct antilock system operation is dependent on tone wheel speed signals from the wheel speed sensors. The vehicle's wheels and tires should all be
the same size and type to generate accurate signals. In addition, the tires should be inflated to the recommended pressures for optimum system operation.
Variations in wheel and tire size or significant variations in inflation pressure can produce inaccurate wheel speed signals; however, the system will
continue to function when using the mini-spare. When driven over rough road surfaces, the rear wheel speed sensor signals may be erratic and cause a
false trouble code (drum brakes only).
