Wheel Speed Sensor: Description and Operation

SENSORS
Wheel Speed Sensors and Tone Wheels: 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. (0.016" to 0.051"). Preferred rear sensor air gap for drum brake systems is 1.1mm (0. 043"). Acceptable air gap range is 0.92mm to 1.275mm (0.036" to 0.050"). 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 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.

G (Acceleration) Switch: The CAB monitors the acceleration switch at all times. The switch assembly contains three mercury switches that monitor vehicle deceleration rates (G-force). Sudden, rapid changes in vehicle and wheel deceleration rate trigger the switch, sending a signal to the CAB. The switch assembly provides three deceleration rates; two for forward braking and one for rearward braking.