Home Diagnosis and TroubleshootingBraking System ABS Sensor – How To Diagnose A Bad Sensor?

ABS Sensor – How To Diagnose A Bad Sensor?

by Jordan Harris
ABS Sensor

Have you noticed some weird symptoms on your car like the ABS light turning on all the time as well as other weird actions by the ABS system? If this is the case, maybe you have a problem with the ABS sensor. But you are at the right place because there will be a lot to cover on this topic where we will dissect everything into small bits.

Having a problem like this can be a really frustrating thing to deal with. Why I’m saying this? Well, this is the case because when you have a faulty sensor you will also have a faulty ABS system. And this system basically means life and death in some situations when you need to do an emergency braking.

This is why these systems were invented and patented. They help you stop on time and also save a lot of lives in the process. Who knows how many people are alive now because of these inventions of car safety overall. This is why you should always make sure that this system is always working perfectly well and doesn’t have any problems. And we are going to help you out with that.

First, we are going to learn what is the ABS system and how does it work. Then we will cover the ABS wheel speed sensor and its method of action. Then we will cover the location as well as the bad ABS sensor symptoms. Lastly, we will look into the ABS sensor replacement and costs. So, if you want to learn more about this problem, please follow along.

What Is The ABS System?

Now before we dive into the ABS wheel speed sensor and its location. Let’s first take a look at what is the ABS system in general terms. Knowing what this system is and how it works will make sorting this problem on your vehicle a lot easier. If you want you can jump right to the symptoms, if not, keep up with us for a bit.

The ABS system is simply an anti-lock brake system. This means that this system prevents the wheels from locking up and causing the car to skid. When the car skids there will be flat spots on the tire and basically the tire will get trashed.

So, this system not only acts as a safety system it also keeps your tire’s health in check. But how this system works under the hood?

Well, it is a really simple system actually. The brain of the system is the control module. The control module is connected to the hydraulic pump that pulsates hydraulic fluid into the calipers to make the car stop without skidding.

Meaning that there is intermittent pressure of the hydraulic fluid that is applied on the brakes in very short intervals. By engaging the brakes this way, you basically avoid the tires skidding.

And most importantly with this system is that the car stops at the shortest distance possible. Unlike without this system where it could stop much later than previously expected and possibly end up crashing the car. But the pump and controller are not the only components that this system has.

There is another very important piece of the puzzle and that is the ABS wheel speed sensor. And more on that we are going to cover in the following chapter.

ABS Wheel Speed Sensor

Now we came to the important bit and that is the ABS wheel speed sensor. What is the ABS sensor? The purpose of the sensor is very indicative in its name.

As you probably assume, this sensor is measuring the speed at which the car is moving. There are four-speed sensors on your car that measure the speed. One sensor per each wheel.

They are mounted on the knuckle. From there they observe how fast the wheel is moving. But this wouldn’t be possible if there wasn’t a device called a tone ring that is mounted on the wheel hub assembly.

This tone ring is the component that the sensor is observing. On the tone ring, there are grooves and each groove is measured as the wheel rotates. There are dozens of these grooves on each of the rings and they basically deliver accurate speed measurements.

If the tone ring is broken, there will be a problem with the anti-lock brake system and you will get the light on the dash. This is why these rings have to be in the best shape if you don’t want to get problems.

Sometimes it is up to them and not the sensor itself. This is why you need to check the tone rings as well because they can get clogged with debris or develop rust. All this will prevent it from normal work.

Nevertheless, the ABS wheel speed sensor is a relatively cheap and affordable component that you could purchase at any parts store and easily replace it. Later on, we are going to dive into the details of how you can do this. Now let’s learn more about the ABS sensor location and see where it is located on the car.

ABS Sensor Location

Now as we covered the ABS wheel speed sensor, let’s now take a look at the ABS sensor location and learn where these sensors are usually located in the car. Knowing this information will help you find the sensor and replace it.

As we already told you, there is a total of 4 sensors on each car. One sensor per each wheel. The sensors are carefully mounted at the rear side of the wheel.

They are basically mounted onto the wheel knuckle. On every wheel knuckle, there is a hole that allows this sensor to be mounted and tightened usually with two screws. Then this sensor is connected to the connector and the harness for the ABS system.

In order to find it, just remove the wheel from the car and then turn the steering wheel completely left or right depending much on which sensor you want to get a hold of, whether the right or the left sensor.

At the rear unfortunately you cannot turn the wheel assembly and you will have to come from underneath or simply do this job blindfolded, relying only on your feel of where the bolts of the sensor are and removing them accordingly.

Another thing you might want to do whenever you remove the sensor is to look at the condition of the tone ring. Make sure that it is in good condition. Rust spots or debris could impair the component to function properly. But what are the bad ABS sensor symptoms? Well, that’s what we are going to cover up next.

Bad ABS Sensor Symptoms

Now as we covered the basics of this system and the components that are involved in it, namely the sensors. Let’s now focus on some other aspects.

And that are the bad ABS sensor symptoms. What type of symptoms can you expect when this sensor is broken and doesn’t work right? Let’s elaborate.

1. ABS Sensor Light

The first in our list of bad ABS sensor symptoms that we are going to cover is the ABS sensor light that often turns on on the dash whenever this component is malfunctioning.

But you should not take this for granted and be 100% positive that the problem is the sensor without doing proper diagnostics with an OBD2 scanner tool.

ABS Sensor

There are other components in this system like the hydraulic pump, controller, tone ring. All of these components can turn this light on as well. So, beware of this.

Before you jump to conclusions, make sure that you get a hold of one of these scanners and see what type of codes you are getting. If some of them indicate problems with the sensors themselves. Then you know where to look at your problem.

If you get errors concerning other components, make sure that you check them accordingly. Now let’s move on to the next symptom.

2. Speedometer Failure

The second in our list of bad ABS sensor symptoms is speedometer failure. As you probably can assume, the ABS sensor is also called a speed sensor.

This means that this sensor is measuring the speed of the car. When the sensor is malfunctioning you will probably get inaccurate readings on the speedometer or the component will completely fail and not show any speed.

Also, the mileage of the car will not be measured and the mileage number will freeze and stay the same. These symptoms are a dead giveaway that you have a problem with the speed sensor and this problem needs solving. But how you can diagnose a bad sensor? Well, that’s what we are going to cover later on in the article.

3. ABS System Does Not Engage (Brakes Locking Up)

The third in our list of bad ABS sensor symptoms is the situation when this system doesn’t engage. As you probably know, this is an anti-lock brake system. Meaning that it prevents the brakes to lock up.

Whenever there is a malfunction on some of the components and the light turns on. It means that this system will not engage when needed. Resulting in the locking up of the brakes under heavy braking.

This will potentially create flat spots on the wheels. But what is worse is that this is a dangerous situation that could cost you dearly.

Imagine that a pedestrian comes up in front of your car and you slam on your brakes, then the brakes lock up and you end up sliding with your car. This is not good for you and for the people around you. You could hurt yourself and also hurt a pedestrian on the road.

So, whenever there is a bad speed sensor, it means that the system is not engaging in the right manner and this situation requires solving as quickly as possible.

4. Pulsating Brake Pedal Under Hard Braking

Another in our list of bad ABS sensor symptoms is the pulsating brake pedal. If one or more speed sensors have failed on your car, can trick your ABS control module to engage even at the slightest pressure you apply on the brake pedal.

It will immediately make the traction control and the anti-brake lock system kick in and activate. Stopping the car with a sheer amount of force without any reason. So, you will feel that pulsating feeling when you apply your foot on the brakes.

In addition to this, there will be the noises that come from the rotors themselves when these systems are activated. Which doesn’t sound any good in reality. You will think that everything went to hell. But this isn’t always the case. The important thing is to note this action and sort out the problem accordingly at a local shop. But can you fix this problem by yourself?

Well, in the following chapters we are going to cover precisely that where we will learn how to diagnose the issue quickly and effectively.

How To Diagnose The Problem?

Now as we learned the basics of this sensor and the bad ABS sensor symptoms. Let’s now dive deeper and learn more about how to diagnose an ABS sensor. How you can pull this off and make proper diagnostics on your car?

Frankly, it is dead easy to do this type of work. Diagnosing speed sensors is really easy and they also are not as expensive as you would probably imagine.

The main thing you will need for this work is an OBD2 scanner tool. With this tool, you will be able to scan the car for codes and learn more about the problems your car has.

If there are some codes that indicate a bad speed sensor, then you know where to look at your problem. The code will also tell you the exact problem that your sensor has. Whether it is a failure in the circuit or the sensor itself.

Sometimes though there can be false positives and is really important for you to delete all the errors and scan the car again and see if they appear. If they do, then you know that you have a problem with a specific sensor.

The next thing you will need is to grab a multimeter tool. With this multimeter tool, you will be able to measure resistance and voltage and see if this sensor is alive or it is completely dead.

For this practice, you can watch the video that we attached above and see how the procedure is done the right way. And here we come to another important problem and that is the ABS sensor replacement. How this is done the right way? Well, that’s what we are going to cover up next.

ABS Sensor Replacement

Now let’s assume that you diagnosed a bad ABS sensor and you are looking at how to replace this component. How this ABS sensor replacement is done.

And the answer is really simple. This sensor is really a good DIY job for any beginner. The important thing for you is to diagnose the problem correctly and locate the bad sensor. That’s something that we explained how it’s done in the previous chapter. So, you might want to watch the video on how you can troubleshoot a bad sensor.

Not it’s time for the replacement process. Replacement is a really easy thing that anyone can do it. The first thing you will need to do is to remove the wheel where the sensor is located.

Then you will have to remove the bolts that are holding this sensor, there are usually two of these bolts. Once removed, the sensor will simply pop out and you will be able to remove it.

Then on the other side, you will need to remove the connector and plug the new sensor into the connector. Then bolt the new component in its place.

Last but not least is to clear all the errors in the car computer and make sure that there are no problems so the brake lights turn off. Then you will be good to go. No more problems for you. But have you asked yourself what is the cost for this part? Well, that’s what we are going to see up next.

ABS Sensor Cost

So, what will be the ABS sensor cost? The cost for this sensor is about $50. Sometimes you can even find deals for $40. It is relatively inexpensive and you will not feel it in your pocket if you go for the replacement route.

For some more expensive cars, they can even go up to $100. Just to clear this out. Not all cars are equal and some of them have more expensive components.

ABS Sensor Replacement Cost

And what does the ABS sensor replacement cost? Well, the average cost to replace a sensor is about $200. $50 for the part and about $150 for the labor.

ABS Sensor

You can also get better deals than this at some places but the average cost is this. This is why sometimes is better to replace it on your own and call it a day.


In this article, we have covered quite a bit when it comes to the ABS sensor. First, we learned how the anti-lock brake system works in practice and why it is so useful.

Then we have covered the symptoms of a bad speed sensor. As we can recall, these symptoms include the light on the cluster, the anti-lock brake system engaging without reason, wrong speedometer values.

Then we covered the diagnosing process and how you can pull this off with a simple OBD2 scanner tool and a multimeter to bench test the sensor and see if it’s any good.

Lastly, we learned the costs that are involved in sorting this problem. For the parts as well as for the labor. And frankly, this is one of the simplest and cheapest works that you could do in a DIY fashion at home.


Now let’s answer some common questions related to this component.

What Is An ABS Sensor

This sensor is also known as a speed sensor. The main goal of this component is to measure the rotations of the wheel and deliver data on the vehicle speed. So, when the sensor notices that there is an abrupt change of speed, it will send this data to the controller and then activate the anti-lock system also known as the ABS system.

Where Is The ABS Sensor Located

This sensor is located behind the wheel. These sensors are usually mounted onto the knuckle at the front and at the rear on the brake drum assembly. They are held by two bolts on one side and are connected via an electrical connector on the other side.

Can ABS Sensor Cause Transmission Problems

No, it cannot cause transmission problems because these components are not related together. This sensor measures the speed and has nothing to do with the transmission. But a longer use of your car with a bad speed sensor can affect other components. This is why you need to replace the component as soon as possible.

How To Tell Which ABS Sensor Is Bad

You can determine this by doing a scan of your car with an OBD2 tool and determining whether or not there is a problem with some of the sensors. If your car has a bad sensor it will throw an error and will indicate the specific component that is affected by this problem.

How To Test ABS Sensor

Testing this component can be done with a multimeter tool. You need to bench test this tool to determine if it has resistance and if it produces a voltage when the wheel is turning. First, you need to understand how the multimeter works and then move on to testing this component.

How To Fix ABS Sensor

Fixing this component is almost impossible if it’s broken. You can try to clean it but it will not help much. This is why the best thing for you would be to replace the component with a new one and call it a day. Replacing it will guarantee that you will not have problems in the future.

What Can A Faulty ABS Sensor Cause

It can cause the brake light to turn on, the ABS light to turn on as well as to engage the traction control and other systems. This is why replacing the component as soon as possible is needed if you want to avoid symptoms to develop.

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