What Are The Symptoms Of A Bad Wheel Speed Sensor?

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Symptoms of a bad wheel speed sensor

Your speedometer is not working correctly? Or did the ABS light turned on? Then you might wonder what are the symptoms of a bad wheel sensor?

Most common symptoms of a bad wheel speed sensor are anti-lock braking system not functioning correctly, traction control or ABS problems highlighted on your dashboard. In addition, you can really feel it when you brake, and it entirely blocks your wheels. This is perilous on public roads, and concerns safety.

What is the wheel speed sensor in a car?

A speed sensor is used to determine the speed value in which a vehicle wheel rotates. In the past a physical cable made the link between the speedometer and the sensor. In fact, the cable was causing a lot of problems because of damage and deterioration.

Having that in mind, we can say that the speed sensor transmits data to the electronic ABS system and other assisting systems for better control of the vehicle.

The construction of the sensor comprises a ferromagnetic part and an active or passive sensor. This video will give you a little more insight into how the speed sensor is working:

The purpose of the speed sensor is to alert if one wheel on an axle is moving faster than the other one. In normal conditions, the wheels rotate at the same speed together, giving a fluid movement of the car.

3 Symptoms Of A Bad Wheel Speed Sensor

The wheel speed sensor is provides information to several vehicle functions like the anti-lock braking system and traction control. Another important function is to send the vehicle speed.

1. ABS is not working accurately

The anti-lock braking system will ensure that your wheels will not block in case of a hard brake. By activating the brake calipers and using the brake pads towards the wheel disc at certain moments in time vehicle can stop safely.

This system is relying on the information that comes from the wheel speed sensors each millisecond. ABS is firstly affected by a bad speed sensor. In this case, not knowing how much pressure to apply can cause critical incidents.

The malfunction can be easily seen when you brake and the front wheels get locked up. In this case is good to check everything because is risky to continue driving.

2. Active traction control LED

There are two possibilities for this to happen. Either you disabled the traction control, or you didn’t and the light is active. In the second’s case probability, something must be wrong.

The traction control is ensuring good traction when high acceleration is applied, but not only. It also helps tyres to catch a grip on the ground in case of a slippery or dangerous road.

Something is wrong if it turns the light of the ABS sensor on. It’s better to check first before driving.

3. Anti-braking lock system light turned on

In case the sensor does not transmit correct information, the electronic control unit that monitors the ABS system will throw an error. This can have multiple causes like not reading correctly the sensor information, disconnection or worn out sensor.

These examples above are not the only things that can cause the ABS led to turn on. Similarly, the ABS pump, low brake fluids or general braking system problem can also describe such behavior of the light turning on.

Since the wheel speed sensor is one cause is always a good idea to also included it on your list of causes.

Where is the wheel speed sensor located?

The wheel speed sensor which is also called the ABS sensor is usually located behind the wheel’s rotor. Depending on the number of sensors that your car has, you can have one per each wheel or one per each front wheels and an additional one on the rear axle.

The four-sensor setup is the most commonly used. With a three-wheel speed sensors setup, we have one sensor for each front wheel and the rear wheels are monitored together.

Can I drive my car with a bad wheel speed sensor?

The speed sensor is providing information to the ABS (Anti-lock braking system). It is very important for this to work because it’s offering essential safety features.

Most of the drivers ignore the LEDs turning ON in the dashboard. When the light is on, it means that the sensors are not working properly. If the sensors are not working, the ABS will stop because it does not receive relevant information.

A disabled ABS system is very dangerous in case of unexpected events. You press the braked pedal, but as the system is off, the system cannot control the rotation of each wheel separately and thus threatening incidents can happen.

Can the speed sensor cause shifting problems?

Although the engine/transmission speed sensor and wheel speed sensor are commonly confused, they have a different function inside a vehicle.

The wheel speed sensor will not cause shifting problems, because it does not give any information to the transmission. Like we discussed above, it can interfere in the good functioning of the ABS or traction control systems.

How can you fix a bad speed sensor?

You can follow some simple steps to check what is wrong with the speed sensor and figure out fixes:

  1. We locate the sensor in the rotor of each wheel or only on the front wheels, depending on the vehicle type.
  2. Uncouple the connector and check it thoroughly. The connector should not have any bent or pushed out pins. For example, you can also press the pins slowly to be sure they are not moving when you insert back the connector.
  3. Check for any rust or anything suspicious on both harness connector and sensor connector.
  4. Check which type of sensor you have – 2 wires or 3 wires. The 2 wires wheel speed sensor does not need a power supply, but the 3 wires will need one.
  5. Use a multimeter to check if the harness has interruptions along the way. Here, you need to set the multimeter on DC voltage (one probe to COM and the other one to V sign) and select a lower scale (max 20V) if it’s not auto adjustable. Don’t forget to put the car contact ON (turn the ignition switch on the first step), then measure the voltage between different pins of the connector (you should get a voltage lower than 12V – the maximum of the battery). You can use these steps to verify a 3 wires harness connected to the sensor.
  6. In case the cables are in good condition, check the sensor. For this, we need to spin the wheels somehow (by lifting the car on a jack and move the wheels easily). It is trickier to check the sensor because we need a voltage supply also, in case of 3 wires sensor. For the simpler, 2 wires sensor you can set the multimeter on AC voltage and check if you get different values when wheels spin. Check this nice video below:


Every symptom of a faulty wheel speed sensor discussed above are a sign that something is not functioning correctly. It is wise to check and correct these issues before going on the road. Risky situations can be prevented, and in fact, we can avoid additional costs.

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