Wheel Speed Sensors on ABS systems

Learn more about the WSS

What is it ?
Wheel speed sensors are a necessary ABS component and sensor input. It is used to inform the ABS control module of rotational wheel speed. There are two types of sensors found on today's vehicles, the passive and the active. The conventional passive sensor consists of a magnetic pin with fine copper wire wrapped around to create a magnetic field. This sensor changes polarity as a toothed metal ring, called a tone ring passes through its field. This tone ring is attached to a part rotating at the same speed as the wheel, such as an outboard CV joint of a front wheel drive or the axle or differential of a rear wheel drive vehicle.

The newer active sensor creates a digital signal. This type of digital wheel speed sensor uses a hall effect or a variable reluctance signal with a square wave pattern. The sensor may have two or three wires. One of which is used as a voltage power supply from the ABS control module. A digital WSS is more accurate at slow speeds. It's also capable of detecting which direction the wheel is turning.
What are the symptoms ?
Common Symptoms
A failing ABS wheel speed sensor can turn on the ABS light and disable the Traction and Stability Control Systems (if equipped). In some cases, the speedometer will stop working and the Check Engine Light will come on.
A malfunctioning ABS wheel speed sensor can cause abnormal braking behavior when braking at low speeds. A dirty sensor can have the same effect and can be "fixed" by cleaning the sensor and the sensor wheel. 

Common Misdiagnoses

Many conditions—including corrosion, worn bearings, or other problems in ABS system—can set a wheel speed sensor trouble code. Any problem with the ABS system needs to be diagnosed before wheel speed sensors are replaced, as a new sensor may not solve the problem.
ABS wheel speed sensors can be easily damaged during other repairs that call for the wheels to be removed (especially brake work). If you have had recent repair work performed, return the vehicle to the shop to inspect for damage.


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Make your online diagnosis
How do I know if my wheel speed sensor needs to be replaced ?

The most common reasons for replacing a wheel speed sensor are damage or contamination. Since the sensor is close to the ground, road debris can cut or fray the wiring. If not held securely in place, the harness may chafe on nearby chassis parts. Since the brake sensor is electrical, exposure to the elements (such as ice and moisture) can cause connectors to corrode or internals parts to short out. A defective or malfunctioning ABS speed sensor will typically set an ABS light on your instrument panel, and trigger an ABS diagnostic code in your vehicles computer. It also may throw a traction control light on as well.
Can I replace an ABS speed sensor myself ?

Replacing the ABS speed sensor varies depending on the vehicle. For vehicles that have the external style sensor, replacement is as simple as unplugging the connector from the vehicle harness and unbolting the sensor from its location. On vehicles that have the ABS brake sensor integrated into the wheel hub and bearing assembly, the job is more involved since the entire assembly will have to be removed, requiring at least the brakes to be taken out of the way.
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