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Wheel Speed Sensor: Everything You Need to Know 

Wheel Speed Sensor: Everything You Need to Know 

Your car relies on numerous sensors in order to properly function. Vintage cars were entirely analog and didn't have the same functionality that modern cars do. And while vintage cars were able to do their job perfectly well, modern vehicles with computers and an array of sensors such as the mass air flow sensor, the oxygen sensor, and the wheel speed sensors are able to operate much more efficiently than their predecessors.

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Without the data from your wheel speed sensor, which works essentially like a tachometer, you wouldn't have data about the actual speed your wheels are moving at to allow your car’s computer to manage your anti-lock brakes and traction control as well as the overall speed of your vehicle. If something goes wrong with your wheel speed sensor then you could have problems not just maintaining the desired speed of your vehicle but with the stability and control of your vehicle as well.


How Does a Wheel Speed Sensor Work?


The wheel speed sensor in your car is made up of a magnet that is wrapped in a coil as well as a sensor ring with teeth on it that is mounted around the CV joint hub. If you know anything about magnets and coils, that creates an electrical field when they're put together. This electrical field creates a signal that can be measured in terms of the number of pulses per second that are created between the magnet coil and the sensor ring. That signal is interpreted by your vehicle's computer which allows it to understand exactly how fast your wheels are rotating and let's it interpret that information to determine whether or not you need your ABS brakes to kick in and take control to help maintain traction among other things. It sounds a little complicated at first, but the system is fairly straightforward and reliable.


 What Happens When a Wheel Speed Sensor Goes Bad?


When your wheel speed sensor isn't working the way it's supposed to then your car is not going to be getting the correct information from it. That can affect your overall performance and can affect the way that your brakes operate. This can be potentially very dangerous if you're expecting your anti-lock brakes to be working when you need them, and they fail on you causing your tires to lock up at the wrong moment. Let's take a look at some of the more common signs and symptoms of a bad wheel speed sensor.


Malfunctioning Anti-Lock Brake System:  Before anti-lock brakes were invented the brakes on vehicles had a bad habit of locking when the brake pedal was applied aggressively. Anti-lock brakes work by applying and releasing the brakes quickly, essentially pumping the brakes for you rather than maintaining constant pressure. When your brakes lock, they can potentially put you into a skidding situation where you completely lose control of the vehicle. Anti-lock brakes prevent this from happening by maintaining better control of the braking system and ensuring your vehicle is more stable as a whole.


 If your wheel speed sensor is not working properly then it's possible that your anti lock brake system will not be working properly either. Because the wheel speed sensor relays information about the speed of your wheels to your vehicle's computer it's responsible for letting your car know when the anti-lock brakes need to be applied and how much pressure they need to exert as well. If this info can't be transmitted to your vehicle's computer then your computer will not know when and if you need brakes applied at all, let alone how aggressively they need to be applied.


 Without this data being transmitted accurately it's possible that when you put your foot on the brakes, they will simply lock completely on you. If this happens on a wet or icy road you could lose control of your vehicle and skid off the road or into another vehicle. If you're noticing that your anti-lock brakes are failing at any point in time you need to get your vehicle into a mechanic as soon as possible to have this addressed. While some repairs can reasonably be put off for a certain amount of time, this is something that you do not want to ignore for any amount of time at all. 


ABS Light:  Because the wheel speed sensor is so closely linked to the ABS system in your vehicle, when something goes wrong with it, it could trip the ABS lights on your dashboard. Typically, the ABS light comes on when the sensor disconnects or wears out but it's also possible that it could be gummed up by grease or road grime in some way that's preventing it from functioning the way it's supposed to. When this occurs, you're going to need to either clean the sensor or replace it with a new one.


 The only problem with properly diagnosing the issue when the ABS light comes on is that it may not necessarily be the wheel speed sensor that caused it to go off. It's also possible that a problem with the brakes themselves, such as bad brake pads or calipers, low brake fluid, a faulty ABS pump, or other issues with your brake lines could cause the ABS light to go off as well. So, if you're not 100% sure you are going to need to go get a mechanic to take a look at it so you can find out the exact nature of the problem. Whatever it is, you never want to take any chances with your brakes, so you don't want to put this one off.


Traction Control Light: Although you are able to actually turn off the traction control in many vehicles, if you haven't done that and the light is illuminated then it's possible the cause is a problem with your wheel speed sensor. Just like with the ABS system, the data from the wheel speed sensor is used to help manage and maintain your traction control system as well. If there's a problem with your traction control as a result of a bad wheel speed sensor you may have difficulty keeping your car straight and properly aligned when driving as a result. 


Slow Stopping: The ABS system works when it senses that you are pressing your brakes hard enough to cause it to activate. If the wheel sensor is not working properly, and you put your foot down on the brake, it may take a moment to get the ABS system to engage properly. The results of that is your car will not be stopping with the immediacy that you're used to. that means it's going to take a little bit longer for your car to come to a complete stop, which could definitely be a serious problem if you are trying to avoid an accident.


Bubbly Brakes:  Normally when your car starts slipping or loses traction on an icy road and you have your foot on the brake pedal you will feel it in your foot as it pumps back and almost seems like it's bubbling. That's the result of the ABS constantly applying pressure and releasing to allow your brakes to engage properly instead of locking up on you. When the wheel sensor isn't working correctly your car may think you're skidding on a slippery road even though you're not. The result will be your brakes meeting your foot with that pumping, bubbling sensation.


Lack of Control: Because the wheel sensor is so vital in maintaining your anti-lock brake system and your traction control system, when you actually need these such as on a slippery wet road or an icy road, you're not going to have the same kind of control that you're used to. That means you are subject to a serious lack of control on a road when it's slippery. You definitely don't want to be driving in a wintry climate if you know that you have a problem with your wheel sensor until such time as you get it fixed. 


 Can You Drive with a Bad Wheel Speed Sensor?


As you can see based on the signs and symptoms of a bad wheel sensor it's entirely possible for you to drive with a faulty sensor in your vehicle but it's definitely not a good idea to do so. In much the same way that you could drive with no headlights if you really wanted to, it doesn't make it a good idea and it will automatically increase the chances that you're going to get into an accident.


Your vehicle will not stop functioning if the wheel sensor doesn't work, but as we've seen your ABS system and your traction systems are both going to suffer serious setbacks as a result in a way that could translate into an accident depending on the conditions in which you're driving. For that reason, if you do feel like you have a problem with your wheel sensor or you are experiencing any of the symptoms that we have described, your best bet is to get to a mechanic as soon as you can for your own safety and the safety of others on the road. 


 How Much Does It Cost to Fix a Wheel Speed Sensor?


Getting the wheel speed sensor on your vehicle replaced can cost you anywhere between about $150 to $250 to get done. This very much depends on the make and model of your vehicle as more expensive or rare models are going to have a greater labour and parts cost associated with them. Getting just the wheel sensor itself may not cost you that much money and some of them can be found on AutoZone for as little as about $20 a piece. However, they can range up to $100 or more so you need to make sure you're getting the right sensor for your particular make and model.


It's also possible that if you're having a problem with your wheel speed sensor malfunctioning you don't necessarily need to actually replace it by buying a new one and swapping the sensor out. Wheel speed sensors are subject to malfunctioning simply because they're dirty. Road grime and other debris can build up on the sensor causing it to not work properly and limiting the data it can transmit to your car’s computer. If that's the case, you can take a rag and wipe the sensor clean to get it functioning again. If you are going to clean your sensor, make sure you don't use any harsh chemicals to do so because that could potentially damage the sensor even worse than just being dirty. If it's really got a lot of greasy buildup you can use a mild soap like Dawn dish soap and some warm water to get it clean. Remember, the sensors are precision tools, and you don't want to be too harsh on them when you're trying to get them clean because you could essentially destroy the sensor completely and make it so that you have no choice but to buy a new one.


The Bottom Line


Most drivers have probably never heard of the wheel speed sensor in their vehicle before, let alone have any idea what it actually does and how it affects the way their vehicle operates. As we can see, the wheel speed sensor does play an important role when it comes to the safety features of your vehicle in terms of traction and the ability to brake, especially in dangerous circumstances. For that reason alone, you need to make sure your wheel speed sensor is working properly all the time. You never want to take any chances when it comes to your ability to brake, especially in an emergency or in bad weather situations.


 If you're finding that your anti-lock brake system or traction control seems to be working much more poorly than it ever used to, there's a good possibility your wheel speed sensor is the culprit so you should be heading to a mechanic to get it looked at. It may be as simple as having it replaced or even just cleaned off again to get your car back in proper working order.