Wheel speed sensors and how we test them have been changing. Currently, two types of wheel speed sensors are in use: magnetic inductive (passive) and magneto resistive (active). Passive sensors have been around since the early days of the anti-lock brake system (ABS). These are the sensors that function on the generator principle. The sensors work with the toothed tone wheels to monitor and provide the anti-lock brake module (ABM) with wheel speed information. The actuator is a toothed tone wheel that rotates with the individual wheel. Each tooth on the tone wheel acts as an actuator for the wheel speed sensor. As the tone wheel rotates, the teeth go in and out of the proximity of the sensor. The result is an alternating current (AC) voltage that is generated in the speed sensor coil by magnetic lines of force fluctuating as the tone wheel passes by the magnetic sensor.
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