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ABS Wheel-Speed Sensor: Operation

As it rotates, the sensor rotor interrupts the magnetic field of the wheel-speed permanent magnet, generating AC voltage in the coil by electromagnetic induction.
The AC voltage cycle changes in proportion to the wheel speed. Wheel speed is detected by the ABS control module by this cycle.
The sensor is mounted so that there is a small clearance between the speed sensor pickup (pole piece) and the sensor rotor.