Wheel Speed Sensor: Description and Operation

Wheel Speed Sensors and Tone Wheels
One active Wheel Speed Sensor (WSS) is located at each wheel and sends a small DC voltage signal to the Controller Antilock Brake (CAB). The CAB sends 12 volts down to the sensor. The sensor has an internal magneto resistance bridge that alters the voltage and amperage of the signal circuit. This voltage and amperage is changed by magnetic induction when a toothed sensor ring (tone wheel) passes by a stationary magnetic sensor (wheel speed sensor). The CAB measures the voltage and amperage of the DC signals for each wheel.

The front wheel speed sensor is attached to a boss in the steering knuckle. The tone wheel is an integral part of the front axle shaft. On LH Bodies the rear sensors are mounted to the rear brake backing plates or rear disc adapters. The rear tone wheels are pressed on the rear hub. The wheel speed sensor air gap is not adjustable. The four wheel speed sensors are serviced individually. The front tone wheels are serviced as an assembly with the outer C.V. joint, housing. The rear tone wheels are serviced as an assembly.

Correct antilock system operation is dependent on accurate 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. Variation in wheel and tires size or significant variations in inflation pressure can produce inaccurate wheel speed signals; however, the system will continue to function when using the correct factory mini-spare.