What is a wheel speed sensor

Replace defective ABS sensor

What are ABS sensors and how do they work?

The anti-lock braking system (ABS) prevents the wheels from locking when braking. The ABS ensures better maneuverability and directional stability of the car when braking. The ABS system regulates the brake pressure when braking, i.e. how hard each wheel is braked. Depending on the surface and its ability to adhere to the road, this should prevent the wheels or a single wheel from locking. Thanks to the ABS system, the vehicle remains controllable and prevents the complete loss of control over a vehicle. The risk of skidding is also considerably reduced thanks to the ABS system.

Different types of ABS systems

The ABS sensor is an important part of the anti-lock braking system. It is the signal transmitter for regulating the brake pressure. In a car there is an ABS sensor on every wheel. This means that four sensors are installed. This means that each wheel can be checked individually. The first ABS were 3-channel systems in which the rear wheels are controlled together. Sometimes only three ABS sensors were used here.

This is how ABS sensors work

The function of the ABS sensors is to measure the number of revolutions on the respective wheel, i.e. how fast each wheel is turning. Because of this function, the ABS sensor is also called a speed sensor. What is meant is the same part. The speed sensor can use a perforated wheel or gear, the so-called sensor ring, to measure how fast the wheels are turning. The sensor rings and the ABS sensor are located on all four wheels

If the wheel speed differs, this is recorded by the speed sensor.

ABS sensors report changes in speed

The speeds recorded during the measurement are sent to the ABS control unit. This determines whether acceleration or heavy braking is taking place. If the brake speed drops on a wheel, it begins to block, which is detected by the sensor ring. This is where the ABS system intervenes to keep the wheels maneuverable. The ABS system can individually prevent the wheels from locking at the front as well as at the rear and thus keeps the vehicle on the road in an emergency.

The ABS intervenes in the braking process

After the ABS sensor has detected the tendency to block, the hydraulic part of the system comes into play. The brake fluid is controlled by solenoid valves and either pumped back or released again. You can tell by the jerking of the brake pedal. This prevents the master cylinder from running empty. Braking would no longer be possible.

Newer ABS systems also take on the function of distributing the braking force to the front and rear. This was done previously via brake force distributors, which were mostly mechanical.

Driving without ABS

If the system fails, there is no need to panic. From then on, the brake circuit works like a normal dual-circuit brake system. Nevertheless, it is important to ensure the driving safety of your car and to change the sensors when they no longer work. In order to determine how the failure could occur, you need specialist knowledge, as the reasons can be from different origins. On the one hand, the sensor can simply be dirty. This problem is treated with special cleaners. If there are other causes of the failure, in most cases the sensor must be replaced. Since there are different types, you should visit a specialist workshop that can install the appropriate sensor.
You should use original parts when changing, as a malfunction affects safety.