Wheel Speed Sensor: Description and Operation

SENSORS
Wheel Speed Sensors and Tone Wheels: One wheel speed sensor (WSS) is located at each front wheel and another mounted to the rear axle. Each sensor sends a small digital signal to the control module (CAB). The CAB sends 12 volts 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 digital signals for each wheel.

The front wheel sensor is attached to the hub housing. The tone wheel is an integral part of the front hub. The rear speed sensor is mounted to the axle housing. The rear tone wheel is bolted to the ring gear inside the rear differential housing. The wheel speed sensor air gap is NOT adjustable. Because of internal circuitry, a resistance check of wheel speed sensors will not determine correct or incorrect function.

Correct antilock system operation is dependent on 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) Sensor: The CAB monitors the acceleration sensor at all times. The sensor assembly contains three mercury sensors that monitor vehicle deceleration rates (G-force). Sudden rapid changes in vehicle and wheel deceleration rate trigger the sensor, sending a signal to the CAB. The sensor assembly provides three deceleration rates; two for forward braking and one for rearward braking. The G-Sensor is mounted inside the CAB and is not separately serviceable.