Wheel Speed Sensor: Description and Operation

CAUTION: The tone wheels used on this vehicle equipped with the ITT Teves Mark 20 Antilock Brake System are different then those used on past models of this vehicle equipped with antilock brakes. Reduced braking performance will result if this part is used on earlier model vehicles and an accident could result. Do not use on pre-1998 model year vehicles.

WHEEL SPEED SENSOR (WSS) AND TONE WHEEL

Front Wheel Speed Sensor:

Rear Wheel Speed Sensor:

One wheel speed sensor (WSS) and one tone wheel are located at each front and rear wheel. Each front wheel speed sensor is attached to a boss in the steering knuckle. The front tone wheel is part of the outboard constant velocity joint. The rear wheel speed sensor on rear disc brake applications is mounted to the rear disc brake adapter. The rear tone wheel is an integral part of the rear wheel hub and bearing.

The four wheel speed sensors are serviced individually. The front tone wheels are serviced as an assembly with the outboard constant velocity joint. The rear tone wheels are serviced as an assembly with the rear hub and bearing assembly.

The wheel speed sensor sends a small AC signal to the Controller Antilock Brake (CAB). This signal is generated by magnetic induction created when a toothed sensor ring (tone wheel) passes the stationary magnetic wheel speed sensor. The CAB converts the AC signal generated at each wheel into a digital signal. If a wheel locking tendency is detected by the CAB, it will then modulate hydraulic pressure via the Hydraulic Control Unit (HCU) to prevent the wheel(s) from locking.

Correct ABS operation is dependent on accurate wheel speed signals. The vehicle's tires and wheels all must be the same size and type to generate accurate signals. Variations in tire and wheel size can produce inaccurate wheel speed signals.

Improper speed sensor-to-tone wheel clearance can cause erratic speed sensor signals. The speed sensor air gap is not adjustable, but should be checked when applicable. Wheel speed sensor-to-tone wheel clearance specifications can be found in Specifications.