Wheel Speed Sensor: Description and Operation

GENEERAL INFORMATION
One wheel speed sensor WSS is located at each wheel and sends a small AC signal to the Controller Antilock Brake CAB. This voltage is generated by magnetic induction when a toothed sensor ring (tonewheel) passes by a stationary magnetic sensor WSS. The CAB converts the AC signals into digital signals for each wheel.

Wheel Speed Sensors:

Front Wheel Speed Sensor And Tone Wheel:

Rear Wheel Speed Sensor And Tone Wheel:

The front wheel speed sensor is attached to a boss in the steering knuckle. The tonewheel is an integral part of the front axle shaft outer C/V joint. The rear speed sensor is mounted in the caliper adapter plate and the rear tonewheel is an integral part of the rear rotor hub. The wheel speed sensor air gap is NOT adjustable. The correct wheel speed sensor air gap is from 0.52 to 1.64mm for the front sensors, and from 0.45 to 1.2lmm for the rear sensors. All wheel speed sensors have a resistance between 800 and 1400 ohms. The four wheel speed sensors are serviced individually. The front tonewheels are serviced as an assembly with the outer C.V Joint Housing. The rear tonewheels are serviced as an assembly with the rotor hub.

OPERATION
Correct ABS system operation is dependent on the wheel speed signals from the wheel speed sensors. The 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 correctly when using the mini-spare.

CIRCUIT OPERATION
There are four wheel-speed sensors, one at each wheel. The sensors use a tone wheel to determine wheel speed. Input to the Controller Anti-Lock Brake (CAB) is done on the following circuits, each of which is a twisted pair: B8 and B9 for the left front wheel (cavity 30 and cavity 15) B6 and B7 for the right front wheel (cavity 6 and cavity 1) B3 and B4 for the left rear wheel (cavity 19 and cavity 28) E1 and B2 for the right rear wheel (cavity 31 and cavity 29).