Wheel Speed Sensor: Description and Operation

ABS Wheel-Speed Sensor
^ The ABS wheel-speed sensors work in conjunction with the rotors to detect wheel revolutions. Each consists of a permanent magnet, coil, and pole piece, and is installed on the knuckle. These produce electrical pulses by monitoring the rotation of the sensor rotors installed on the drive shafts and the wheel hubs.

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.

Fail-Safe Function
^ The ABS control module has a fail-safe function. When this function senses a malfunction in the ABS, the valve relay cuts the power supply to the hydraulic unit solenoid valves, and the system returns to normal braking.
^ The ABS warning light illuminates.

On-board Diagnostics








^ The ABS control module includes an on-board diagnostic function, which checks for normal operation of the ABS.

ABS Warning Light





^ Normal condition
^ Occurrence of malfunction





1) In case of present failure (includes failures that reappear during operation only, such as in the ABS sensor rotor malfunction)








2) In case of past failure (Malfunction detected in wheel-speed sensor or pump motor circuit)
^ The ABS warning light is located within the instrument cluster. If the warning light illuminates during driving, it indicates a malfunction in the ABS system.
^ The following conditions indicate a malfunction in the system.
1) The warning light does not illuminate when the ignition switch is turned to ON.
2) The warning light remains illuminated after the ignition switch is turned to ON.
3) The warning light illuminates or flashes while driving the vehicle.
^ In the case with past failures, the next time the engine is started, if the control module verifies that the system is normal, the ABS warning light goes out.
^ However, with the malfunctions in the ABS wheel-speed sensor or pump motor circuit, verification cannot be done without driving the vehicle.
^ Drive the vehicle over 10 km/h (6.2 mph), and if the system is verified to be normal, the warning light goes out.