Wheel Speed Sensors and Tone Wheels
Front Wheel Speed Sensor:
Rear Wheel Speed Sensor:
PURPOSE
One Wheel Speed Sensor (WSS) is located at each wheel, and 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 WSS. The CAB converts the AC signal generated at each wheel into a digital signal.
OPERATION
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.
ASSEMBLY AND LOCATION
The front Wheel Speed Sensor is attached to a boss in the steering knuckle. The tone wheel is part of the outboard constant velocity joint. The rear Wheel Speed Sensor on rear drum brake applications is mounted to the rear brake support plate and the rear tone wheel is an integral part of the rear wheel hub and bearing assembly.
SERVICE INDIVIDUALLY
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.
CORRECT OPERATION DEPENDENT ON ACCURATE SIGNALS
Correct ABS system operation is dependent on accurate wheel speed signals. The vehicle's wheels and tires must all be the same size and type to generate accurate signals. Variations in wheel and tire size can produce inaccurate wheel speed signals.