Wheel Speed Sensor
The wheel speed sensor is the essential component the ABS ECU (ESP/Electronic Stability Program) because the ESP calculates vehicle speed and determines whether wheel lock occurs based on data from the sensor.
For example, front-wheel vehicles use speed of a faster rear wheel as a reference when determining vehicle speed, and, if the vehicle detects difference in speed between front and rear wheel, ABS control sets in.
Wheel speed sensor is active hall-sensor type.