Wheel Speed Sensor: Description and Operation

WHEEL SPEED SENSOR (WSS)














Figs. 3 through 6

At each wheel of the vehicle there is one wheel speed sensor (WSS) and one tone wheel. Each front wheel speed sensor is attached to a boss in the steering knuckle. The front tone wheel is part of the driveshaft outboard constant velocity joint. The rear wheel speed sensor is mounted to the rear disc brake adapter. The rear tone wheel is an integral part of the rear wheel hub and bearing.
The wheel speed sensor operates on electronic energy supplied by the CAB and outputs a square wave signal whose current alternates between two constant levels. Its frequency is proportional to the speed of the tone wheel. The output is available as long as the sensor is powered and its state (high or low) corresponds to the presence or absence of tone wheel teeth. The output signal is sent to the CAB. If a wheel locking tendency is detected by the CAB, it will then modulate hydraulic pressure via the 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.