What does an ABS Sensor do?

The wheels of a moving vehicle can move at different speeds, with some turning faster than others. This can cause a loss of steering control and compromise safety on the road. To mitigate this, speed wheel sensors are used to monitor the speed of the wheels and send electrical signals to electronic driving safety systems to maintain vehicle control and braking.

These safety systems include the Anti-lock Braking System (ABS), Electronic Stability Program (ESP), and traction control systems, and all depend on the wheel speed sensors to function. As a result, a failing speed sensor will cause these systems to malfunction.

How Do Wheel Speed Sensors Work?

The wheel speed sensors must remain in the same position to detect the rotation of the tires, so they are mounted on the stationary portion of the hub assembly and pointed towards the reluctor ring. The reluctor ring is a timing ring with multiple toothed gears mounted in the rotary portion of the hub assembly.

As the wheels spin, the teeth of the reluctor ring pass by the wheel speed sensor, which detects the pattern of the teeth and how quickly they pass its magnetic fields or wire coils. This data is transferred to the ECU to determine the direction and speed of the wheels' rotation.

Why Are Wheel Speed Sensors Important?

Safety is a key reason why wheel speed sensors are necessary. By monitoring each wheel separately, they provide the ECU with accurate data, which helps drivers know the speed at which their vehicle is moving. Without this information, drivers cannot precisely know their car's speed, which compromises safety on the road.

During braking, the speed sensors inform the anti-lock braking unit through the ECU, which wheels are locking up or turning slower than others. This triggers the ABS to intervene by quickly pumping the brakes at the locking wheels, allowing them to keep spinning and helping the driver avoid dangerous skids.

Additionally, the Vehicle's Stability Control (VSC) system, or traction control system, uses the data from the speed sensors to maintain vehicle control by reducing power to faster-spinning wheels and increasing power to slower-spinning wheels.

Signs of a Failing Wheel Speed Sensor

The following are sign the you speed sensor become faulty:

• Illuminated ABS warning light. If the wheel speed sensor is disconnected, worn out, or damaged, the anti-lock braking system (ABS) will trigger a warning light on the dashboard.
• Illuminated Traction Control light. A failing wheel speed sensor will activate the traction control light without driver input because it's no longer receiving signals from the sensors.
• Wheels locking up during braking. If the wheel speed sensor is failing, the anti-lock braking system (ABS) will not be able to read the speed of the wheels, causing the wheels to lock up during braking. Additionally, the speedometer may be disabled since it is not receiving information from the speed sensors.