Question 1

When an ABS sensor needs replacing

Accepted Answer

The ABS sensor measures wheel rotational speed and feeds it to the ABS unit. When the sensor fails or its magnetic ring gets contaminated, the ABS unit no longer receives correct information and the ABS light comes on. The system falls back to backup mode — normal braking works, but ABS functions are disabled.

Diagnostics reveals which wheel is affected (P0365–P0373 codes). A sensor fault is much cheaper to fix than a full ABS unit replacement, so thorough diagnosis before decisions is important. On some cars the ABS sensor is integrated into the wheel bearing, in which case the whole bearing needs replacing.

Question 2

How an ABS sensor is replaced

Accepted Answer

The wheel is removed and the sensor wiring is traced back to its source. The sensor is usually screwed into the wheel hub near the hub's magnetic ring. The old sensor is removed — often it's rust-welded in and requires heating.

The sensor mounting point is cleaned with a wire brush and the new sensor is installed. The electrical connector is reconnected and the diagnostic tool clears the old fault codes. The test drive confirms the ABS light is off and the system works normally. An emergency brake test on a slippery surface confirms ABS operation.

Question 3

Why do ABS sensors fail?

Accepted Answer

ABS sensors are continuously exposed to weather and road conditions. In Finland road salt and moisture cause corrosion in the sensor's electrical connections. Magnetic ring contamination from brake disc wear metal can also give wrong readings. Stone strike or mechanical damage is a third common cause — if the car hits a pothole hard, the sensor can break.

ABS Sensor Replacement in Vantaa