Wheel Speed Sensor: Description and Operation

The wheel sensors are mounted near a toothed sensor wheel at each wheel.
Each time a tooth on the sensor wheel passes the sensor, it distorts a magnetic field, which causes a signal to be sent to the Engine Control Unit (ECU).
The rear wheel sensor is designed differently than the front, in that it is less sensitive to wheel bearing play and starts to pass information to the control module at very low wheel speeds.