Testing A Wheel Speed Sensor

By Author: Mark Sanford
Total Articles: 38
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Every year, manufacturers add new features to their vehicles to make them safer and more economical to drive. Wheel sensors are part of the ABS system, which keeps the brakes from locking up when you have to hit them hard. The wheel sensor also has additional functions including sensing the speed of the wheels and working with the traction and stability control systems.

SYMPTOMS OF FAILING OR FAILED ABS WHEEL SPEED SENSOR
In some cases, you might notice symptoms of a failing wheel sensor, or it might fail completely with no warning. Common symptoms of a failing or failed ABS sensor include:

• One of several warning lights may come on including the ABS light, the traction control light, or the stability control light. In some cases, the speedometer may stop working.
• Your ABS system may not work. If the ABS computer senses a problem with the wheel sensor, it might disable the entire ABS system. This depends on the make and model of your vehicle.
• You might lose the traction control system, the stability control system, or both.
• If you have roll stability and hill-start assist, ...
... those systems could stop working.

The ABS wheel speed sensor uses a magnetic core and an ABS ring to create an electronic signal, which is then sent to the computer. The signal gives the computer information such as wheel speed to help the computer determine if you are spinning the drive tire or if the brakes are locked up. If you have a hall-effect sensor, the sensor works differently to create the signal, but forwards the same information to the computer. Hall-effect sensors send a reference voltage to the sensor. Different voltages mean different things happening with the wheel.

TESTING AN ABS WHEEL SPEED SENSOR
If your vehicle’s wheel speed sensor is faulty, you should replace it as soon as possible. In most cases, you simply remove the bracket bolt and unplug the sensor’s electrical connection to remove it. Here’s how to test the ABS sensor:

• Park on level ground and set the emergency brake. Jack the vehicle up and support it with jack stands. Never rely on a hydraulic jack to hold a vehicle up while you are under it.
• Remove the electrical connector from the wheel speed sensor.
• Set the voltmeter to AC voltage. Touch the test probes to the leads on the sensor.
• To create voltage, spin the wheel. You will see different voltages depending on the speed the wheel is spinning. As the wheel spins faster, you should see higher voltages. As the wheel slows, you should see the voltage drop. If you do not see voltage, the sensor is bad.
• If your vehicle is showing a wheel sensor code, but the sensor tests good, you could have an electrical problem. You can check the wires by setting the voltmeter to ohms and testing each end of the wires going to the wheel sensor to find an “open,” or a bad wire.
• If the wires and sensor are showing good, you could have a defective computer, especially if you get several erroneous codes from the ABS computer.

If the wheel sensor is bad, be sure to match the new wheel sensor with the original one to make sure the parts store gave you the correct sensor. Part numbers might be different, but the sensor’s physical attributes, such as length, diameter, and wiring should be the same. Once you replace the sensor, take the vehicle for a test drive to make sure everything is working properly.

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