How does ABS Wheel Speed Sensor Work? | What are the Symptoms of a bad ABS Sensor?

The anti-lock braking (ABS) system is one of the most important parts of your vehicle. It ensures the efficient working of your car. This system contains multiple sensors that deliver information to the ABS module to activate it when the wheels lock. The ABS wheel speed sensor mechanisms are located on the wheel and generally consist of two parts. The ABS sensor configurations vary according to the vehicle model.

Conventional vehicle models may only have one or two sensors throughout the vehicle, but the latest models usually contain one sensor on each wheel. When your ABS sensor or ABS wheel speed sensor fails, your vehicle generates various warning signs to let you know there is a problem. This article mainly explains the bad ABS wheel speed sensor symptoms, causes, and replacement cost.

What is an ABS Sensor?

The ABS sensor is also known as an ABS wheel speed sensor or ABS brake sensor. The ABS system contains an ABS wheel speed sensor that measures the rotational speed of the wheel and delivers this data to the ABS computer. The ABS computer utilizes the ABS sensor data to stop the brakes from locking during an emergency stop.

ABS Sensor

The latest vehicle models usually contain an anti-lock braking (ABS) system. This system further contains multiple ABS wheel sensors. These sensors are installed at the vehicle axle or wheels to calculate the speed of the wheel. The ABS sensors usually have a toothed ring and magnet surrounded by a coil.

The contact between the toothed ring and magnet produces an electric field that is delivered as a signal to the ABS controller.

When the controller receives the signal, it utilizes the signal to determine the exact speed of the vehicle wheels. This data is then sent to the Powertrain Control Module (PCM).

The ABS system of your car activates when the PCM detects that the car wheels are locked. This system works so fast that it also produces a pulsating grinding noise.

If your car also has a traction control system, your ABS sensor will also help regulate the car’s movements in unstable conditions. As the traction is lost, one wheel’s speed differs from the others, which may activate the traction control system.

Symptoms Of a bad ABS Wheel Speed Sensor

As the ABS wheel speed sensor goes bad, it produces one of the below-given symptoms:

  1. ABS light Illumination
  2. Loss of Anti-lock Brakes
  3. Brakes take longer to stop car
  4. Disability of the Traction or Stability Control System
  5. Pulsating Brake Pedal while braking
  6. Car Becomes Unstable during Braking

1) ABS light Illumination

The vehicle dashboard has multiple warning lights and symbols. These warning lights and symbols indicate different problems. The ABS light illumination is one of the most common symptoms of a bad ABS wheel speed sensor.

ABS Light

The ABS light is the same as the Check Engine Light except for the ABS system. Illumination of the ABS light is an indication that there may be a problem with the ABS system or one of the ABS sensors.

Read More: Causes of ABS Light Illumination

2) Loss of Anti-lock Brakes

The faulty ABS wheel sensor may lead to the failure of the anti-lock brakes. Whenever your system detects a problem, it activates an alarm, and the ABS warning light starts illuminating.

In such a condition, your car’s PCM will no longer receive any proper information from the sensors. The PCM uses this data to find if the wheels are locked and need support.

The system doesn’t know what’s going on, so the ABS turns itself off until the repair is complete.

Read More: Bad PCM Symptoms and Causes

3) Brakes take longer to stop car

If you brake hard, the ABS system must automatically engage and slow the car to minimize skidding and traction loss. You should try to develop a regular driving habit that prevents you from hard braking conditions. However, if your car takes a long time to stop in hard braking conditions, facing skidding or traction loss, there may be something wrong with your ABS system.

Brakes take longer to stop car due to bad ABS wheel speed sensor

If your car brakes take a longer time to stop the car, there may be an issue with your ABS sensor. The faulty sensors may lead to braking problems.

4) Disability of the Traction Control System

The anti-lock braking system is not the only component that depends on the ABS wheel speed sensor data for proper functioning, but the traction control system can also utilize data from the ABS sensors to perform stability control, hill-start assists, and many other functions. A defective ABS sensor may stop the operation of the traction control system.

Traction Control System

5) Pulsating Brake Pedal while braking

The main function of the ABS sensor is to determine the speed of each wheel and transfer this data to the PCM.

Pulsating Brake Pedal

When your sensor goes bad, it doesn’t measure the exact speed of one or more wheels. In this way, it sends wrong information to ABS computer and PCM. This tricks the ABS computer into thinking the vehicle is skidding on a slippery surface. This activates the ABS system and traction control system and lets you feel the pumping or pulsating brake pedal when braking.

6) Car Becomes Unstable during Braking

In normal operation, the ABS system turns on under hard braking to immediately lower the speed of your car without locking the brakes and causing the car to skid.

The ABS sensor utilizes the information that it gathers to adjust the brake pressure to avoid lock-up and traction loss during emergency braking. Especially on wet or icy roads, it becomes more difficult to prevent the brakes from locking up and skidding.

ABS Wheel Speed Sensor Location

The ABS wheel speed sensor is most commonly located at the wheel just behind the wheel brake rotor but is sometimes also installed directly on the axle. The number of ABS sensors varies according to the vehicle model.  

ABS Wheel Speed Sensor Location

Some ABS system includes four ABS wheel speed sensors, one for each wheel located behind the brake rotor. Some systems contain only three sensors, two sensors for each front wheel and one for the rear axle instead of at the rear wheels.

The ABS type tells the number of sensors the vehicle has. There are four ABS settings here.

  1. 4-sensor ABS: Each wheel has a sensor and is measured individually. This is the most common setting on the latest vehicle models.
  2. 2-channel 4-sensor ABS: In this type, each wheel contains one sensor, but there is one channel in the rear and one channel in front. If the speed sensor detects that the wheels are locking, ABS will activate on that part of the car.
  3. 4-sensor 3-channel ABS: In this type of ABS system, one sensor is located at each wheel of the vehicle, but the rear wheels are driven by a controller.
  4. 3-channel, 3-sensor ABS: In this type, one sensor is installed at each front wheel, and one sensor is installed on the back axle. The front wheels are gauged individually, while the rear wheels are checked simultaneously.

How to Replace an ABS Speed Sensor

You must have the following tools to replace the ABS wheel speed sensor:

  • Wheel chocks
  • Jack and jack stands
  • Torque wrench
  • Safety glasses
  • Ratchet and socket set
  • Vehicle manual

Follow the below-given steps to replace your ABS wheel speed sensor:

  1. First of all, wear safety goggles and gloves.
  2. Disconnect the negative terminal of your battery.
  3. Use a jack and jack stand to carefully raise and support your car. Apply the parking brakes and stop the motion of the rear wheels.
  4. Remove the electrical connectors from the ABS sensor harness.
  5. Locate the faulty ABS sensor. Read the diagnostic trouble code by using a scan tool and identify the faulty sensor. If you don’t see a code, use a scanner to monitor the sensor data while driving.
  6. Take a ratchet to detach the broken ABS sensor mounting bolts. Also, remove the clips that hold the sensor wiring harness.
  7. Now remove the faulty sensor from the vehicle.
  8. Compare the new ABS sensor with the old one to ensure their design.
  9. Use brake cleaner and sandpaper to clean the sensor mounting holes before installing the new sensor.
  10. Install the new sensor.
  11. Install the sensor mounting screws and wiring harness retaining fasteners. Tight the fasteners using a torque wrench according to manufacturer recommendations.
  12. Reconnect the sensor electrical connectors.
  13. Safely remove the jacks and lower the car.
  14. Reconnect the negative terminal of the vehicle battery.
  15. Clear any associated Diagnostic Trouble Code (DTC) using a scan tool.

ABS Wheel Speed Sensor Replacement Cost

The replacement cost of the ABS wheel speed sensor varies according to your vehicle model, labor cost, and your living cost.

The average replacement cost of the ABS wheel speed sensor is from $180 to $420. In this cost, the labor cost is from $90 to $280, while the cost of each cost is from $90 to $140

FAQ Section

What is the function of the ABS Wheel Speed Sensor?

The ABS wheel speed sensor measures the speed and rotation of the wheel and sends this information to the ABS computer to optimize both brake and traction control via the ABS.

Can the ABS wheel speed sensor be cleaned?

Yes, you can clean the ABS sensor, but that probably will only partially fix the issue. Electrical issues and open circuits are the major causes of a faulty ABS sensor. If your ABS relutor ring is badly rusted, it may also lead to the wrong reading of the sensor.

What causes ABS sensors to go bad?

There are several factors that can damage the ABS sensor. The dust or dirt that builds up on the sensor is one of the major causes of the faulty sensor. This may happen with the passage of time since the sensor is installed in an open place, especially if you live in a dirty or dusty area.

The corrosion may also lead to the failure of the sensor. This can happen if water gets into the ABS system. The physical damage to the sensor itself may also damage the sensor.

Can you clean ABS sensors?

With the sensor detached, take a rag and clean the sensor. I don’t want to use chemicals on the sensor to avoid possible problems. However, if the sensor is heavily soiled, use a mild detergent solution to wash it. ABS sensors are precision instruments for harsh environments.

How do you know which ABS sensor is faulty?

A bad ABS sensor generates one or more of the below-given symptoms:

  1. ABS light Illumination
  2. Loss of Anti-lock Brakes
  3. Brakes take longer to stop car
  4. Disability of the Traction or Stability Control System
  5. Pulsating Brake Pedal while braking
  6. Car Becomes Unstable during Braking

How many ABS sensors are on a car?

The number of sensors in a vehicle varies according to the vehicle model. Mostly, the vehicles contain as few as one or up to four ABS sensors. 

How to clean an ABS wheel speed sensor?

With the sensor free, take your rag and wipe the sensor until it’s clean. It is recommended not to use a chemical on the sensor to avoid serious issues. If your sensor is really dirty, use a mild soapy solution and rinse well. The ABS sensors are precision instruments in a crude environment.

Can I drive with a bad ABS sensor?

Yes, you can drive, but driving with bad ABS sensors or an ABS warning light is not recommended. The illuminated ABS warning light indicates that there is something wrong.

The bad ABS sensors may produce different drivability issues, including skidding or poor acceleration. Your car may not be able to stop on slippery roads as it is designed to stop if you brake hard. Therefore, you should immediately contact a specialist whenever your sensor goes bad.

Can I drive with a bad ABS system?

Driving with a bad ABS sensor is not recommended. A bad ABS system may also affect other safety mechanisms, such as electronic stability control and traction control. Therefore, driving with a bad ABS system is very hazardous.

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