Different Types of Wheel Speed Sensors and Their Significance

Wheel speed sensors, also known as ABS sensors, monitor the speed of wheel rotation. These sensors constantly monitor the speed of the wheel’s rotation and send it to the ABS control module. Since these have a functional role in control parameters, wheel speed sensors are an important automobile component that must be well-maintained. 

To ensure the effective function of ABS, there are different types of wheel speed sensors. Each has an important role to play. Today, we will take a look at these types and their functions to get a better understanding of how ABS works. 

Wheel Speed Sensors or ABS Sensors

The wheel speed sensors are also called ABS sensors or ABS brake sensors. Wheel speed sensors keep a check on the rotational speed of each tyre and report its performance to the car’s Engine Control Module (ECM). In cars, every wheel has a different turning speed. Based on the sensor’s data, the ECM analyzes if any of the wheels are locking up. 

These sensors work closely with complex electronic systems of the vehicle to ensure proper driving dynamics, lower fuel consumption, and lower gas emissions. The ABS control unit sends the wheel speed information received by speed sensors via data lines to various vehicle systems.  

Types of Wheel Speed Sensors – Active and Passive

There are two types of wheel speed sensors: the active sensor and the passive sensor. 

Active Wheel Speed Sensors

The wheel speed sensors that are categorised as active sensors have a stark difference from the passive speed sensor. The active wheel speed sensor is said to be “activated” only when supplied with a voltage and generates an output signal. There is a digital signal created by active wheel speed sensors sent to the ABS control unit.

Active wheel speed sensors are also called magneto-resistive because they contain a sensing element that is connected to a magnetic element or a two-pole electric cable. The active sensor is more efficient than a passive sensor because digital signals are more accurate at slow speeds and capable of detecting which direction the wheel is turning.

Passive Wheel Speed Sensors

Also called inductive or variable-reluctance magnet sensors, passive speed sensors operate without requiring an additional supply of voltage. It is positioned above the impulse wheel which is connected to the drive shaft. The sensor detects the speed when the impulse wheel rotates, resulting in a change of winding from tooth to tooth that in turn generates a change in the magnetic flow. The passive sensor creates an AC signal with fluctuating frequencies according to wheel rotation speed, which is then converted to a digital signal by the ABS control module. 

Therefore, the front of the rear wheel speed sensors works with or without a defined voltage from the ABS control unit. As a result, the ABS sensors make sure the car does not slide or skid when brakes are applied. 

What Causes Wheel Speed Sensors to Stop Working?

Now that we know the types of wheel speed sensors, we know how important components they are to the optimal functioning of a vehicle. Understanding the causes of malfunctioning wheel speed sensors is important to know where to look for damage and take precautionary measures to avoid the problem. 

1. Heavy contamination or debris is a primary cause of failure. 
2. Broken wiring of the speed sensors that can disrupt signal generation and detection.
3. Since speed sensors also work with voltage, internal short circuits will cause them to fail. Read here to know about the causes of short circuits in a car along with solutions.
4. Driving with increased wheel bearing clearance is another reason.
5. Mechanical damage to the wheel encoder, which detects the rotation of the motor, can adversely affect the wheel speed sensor.
6. Any other kind of external damage can impair the speed sensors.

Things to Know About Wheel Speed Sensors

1. Wheels of a car come with either rotors or rear drums. The tyre that has a rotor in it will also have a speed sensor, whereas, the tyre with the rear drum will have a one-speed sensor in the rear and two-speed sensors in the front. 
2. As mentioned earlier, you need to keep the sensors clear of dirt and debris to avoid malfunctioning. If the sensors remain dirtied, they will stop working. In that case, it needs replacement or proper cleaning by the mechanic. 
3. There is at least one-speed sensor in each wheel. It makes it possible to replace only the one-speed sensor should the need arise. 
4. The Traction Control System (TCS) relies on wheel speed sensors as do the ABS control unit. If there is an issue in both the systems, it can be fixed by replacing the speed sensors.

What are the Signs of Faulty Wheel Speed Sensors?

The signs of a faulty wheel speed sensor are as follows: 

1. The ABS warning light switches on in the dashboard
2. The traction control system (TCS) warning light is on 
3. The wheels lock during the brakes 
4. Fault code is stored
5. Loss in traction when driving on slippery road conditions

Depending on the type of wheel, there can be one to four ABS sensors on each wheel. The wheel speed sensors are pivotal to the functioning of the ABS of a vehicle. The two types of wheel speed sensors tell the ABS control unit when to unlock the brakes.

Besides, if the wheel speed sensors have completely failed, you can replace them. You can easily find wheel speed sensors online from auto accessories and parts stores in the UAE or from a physical store, Since you now know the types of wheel speed sensors and signs of a bad one and how to diagnose the fault, make sure when buying a used car in the UAE, it has fully-functional wheel speed sensors.