Your car’s ECU collects data from its numerous sensors, one of which is the speed sensor. This device is arguably most critical to your vehicle’s safety because it measures the rotational speed of each wheel and sends that data to the ABS and stability systems to help you drive safely.

You shouldn't drive your car if it has a failing speed sensor. Even if the car still seems drivable, failing speed sensors will cause the car to behave erratically by sending wrong signals to the ABS and stability systems and put you at risk.

There are many things you need to know about each speed sensor in your car, and this article will help you understand better.

Let’s get started.

What Are the Different Speed Sensors?

First, it's crucial to understand that there is more than one kind of speed sensor in your car. Unfortunately, things can get confusing because people use many terms for it, and sometimes interchange it with other speed sensor names.

You might be familiar with the Vehicle Speed Sensor (VSS), which measures the transmission output speed.

That's a separate sensor from the one we're focusing on in this article. Here, we'll dive deep into the Wheel Speed Sensor (WSS) instead.

This speed sensor’s location is in each wheel hub or rotor. Unlike the VSS, which measures the transmission output speed, the WSS measures how fast each wheel turns.

The Wheel Speed Sensor (WSS) is also referred to as the ABS Speed Sensor because it is a critical component in your car’s Anti-Lock Braking System (ABS).

What Does a Wheel Speed Sensor Do?

Wheel speed sensors work in a very straightforward manner. 

As mentioned above, there’s a WSS attached to each wheel on your car. Each one continuously measures the wheel's rotating speed as you drive down the road. These sensors can also determine the direction in which the wheels are turning so your car knows if it's going forward or backwards.

All that data about the wheels’ rotation is then supplied to your car’s ABS or stability system control unit for processing.

When the WSS are working correctly, the ABS or stability systems can then manipulate the brakes and wheels to ensure that your car has the traction it needs to remain stable and keep you in control.

What Are the Symptoms of a Faulty Speed Sensor?

So how can you tell if any of the WSS is faulty? Since they are attached to each wheel rotor, they’re out of your sight as you drive, and besides, you can’t say that a speed sensor is faulty just by looking at it.

So, again, how?

Thankfully, the symptoms of a bad wheel speed sensor are immediately noticeable. There’s no way you’ll overlook those symptoms, so you’ll know right away if your speed sensors are failing.

Here’s how your car will behave when one or more speed sensors stop working correctly:

• Warning lights: A failed speed sensor will trigger one or more warning lights on your instrument panel. More specifically, you'll see the ABS or stability control warning lights illuminate or flash on your dashboard to let you know something's wrong.
• ABS problems: Aside from visual indicators, performance issues are also clear signs that your speed sensors are failing. For example, the ABS will stop working or only work erratically. That's because failing speed sensors will send incorrect data about each wheel's rotation speed to the ABS, causing it to react strangely.
• Traction and stability loss: Your vehicle's speed sensors also affect any traction or stability systems the car might have. So, failing speed sensors supply incorrect data to those systems, causing the loss of traction or stability when you need it the most.
• Unstable braking: Lastly, erratic braking can also point to one or more failing speed sensors. More specifically, you'll feel your brake pedal pulsating as you push down on it with your foot.

As you can see, these failing speed sensor symptoms are almost impossible to ignore. Once you experience one or more of them, you should get your car to your mechanic as soon as possible.

It's unsafe to continue driving when those symptoms start to happen.

What Causes Wheel Speed Sensor Failure?

Each wheel on your car has a speed sensor of its own. While they are out of the way, there are many ways that each sensor can experience damage and failure, such as:

#1 Corrosion

As you might already know, corrosion causes many car problems, and the same is true for speed sensors.

Simply put, the older your car is, the more its speed sensors are corroded to the point that they stop working correctly.

#2 Road Debris

A speed sensor measures a wheel's rotational speed and direction. Unfortunately, that part of your vehicle kicks up plenty of dirt and debris, some of which can end up blocking the speed sensor.

With too much debris in the way, the sensor can’t measure the wheel’s speed.

#3 Mechanical Damage

Dirt and debris aren’t the only things a wheel might kick up to the sensor. Imagine rocks and other hard objects doing the same thing, causing mechanical damage to the speed sensors.

#4 Excess Wear

As with all car components, your speed sensors might stop working simply because of excess wear, which becomes more likely as your vehicle ages. It can also happen sooner if the sensors you use are of low quality.

Can You Drive with a Failing Wheel Sensor?

No, you can't and shouldn't drive with a failing wheel sensor because it significantly undermines your vehicle's safety.

Your car has plenty of sensors, each sending data to different systems. Speed sensors, in particular, affect the functionality of the ABS and stability systems, which are critical to your vehicle’s safety. When a faulty speed sensor sends wrong data, those systems will go haywire.

So, if your car’s speed sensors are failing, you’ll have to get them checked by a mechanic immediately. Use CarpartAU’s Directory to find mechanics in your area who can help you fix the problem.

By Ray Hasbollah