ABS Sensor

The ABS sensor is also known as the Wheel Speed Sensor. The job of the sensor is to provide a digital signal to the car's ECU that reports the speed of each wheel.

This function is vital for ABS to operate as without speed readings from the wheels the ECU cannot determine whether a wheel is locking up under braking. When the ECU detects a wheel is turning at a speed slower than is possible relative to the other wheels it will engage the ABS system to manage braking on the wheel. Once the wheel then returns to a normal speed it will re apply the brake (via the abs pump). This process repeats up to 20 times per second and is responsible for the grinding sensation you sometimes feel when you apply the brakes.

If the sensors malfunction this vital safety system cannot work correctly. It's not always clear if the sensors are failing as other issues can make them appear to be the culprit. Any problems or warnings from the ABS should be investigated by a qualified mechanic.