A wheel speed sensor is part of the anti-lock braking system (ABS) and traction control system on your vehicle. Actually, there are four wheel speed sensors, one for each wheel. The job of a wheel speed sensor is to detect the rate of speed at which your wheel is spinning. That information is sent to one of your vehicle’s computers where wheel speed is constantly monitored.
The way that a wheel speed sensor works is through the use of magnets. A metal ring attached to each wheel hub has a series of ridges around the edge. The wheel speed sensor magnets (mounted nearby) sense these ridges and convert the magnetic field that is generated as a result into an electrical signal that is relayed to the computer. The computer takes the speed of the wheel into consideration when it decides whether to engage the ABS control unit (or the traction control).
To replace a wheel speed sensor, a technician must first raise and support your vehicle off of the ground for access. The wheel and tire must also be removed. From there, the process differs greatly from one vehicle make and model to the next. That is because of the way each manufacturer locates and mounts the sensor.
Some vehicles integrate the wheel speed sensor into the wheel hub assembly. In those cases, the wheel hub must be changed in order to replace the sensor. Other manufacturers place the sensor in a mount on the steering knuckle where the wheel hub is mounted. In those instances, the sensor might be simply unbolted and dislodged. But the sensor is often corroded in place and needs to be extracted with care.