Bad ABS Sensor Symptoms


Modern cars are equipped with all manner of sensors, which help the various control modules in the car make adjustments to help the car drive better. However, if one of these sensors fails, it can have a chain effect and end up affecting several other components of your car.

The ABS (anti-lock braking system) sensor is one such sensor. If one of the ABS sensors in your car goes bad, you’re most likely going to notice it when you’re braking; in particular, you’ll find that your brakes are less effective on slippery surfaces, and it’s likely that your car will lose traction on such surfaces as well.

Today, we’ll be going over the purpose of the ABS sensor and how it works. We’ll also be describing the symptoms of a bad ABS sensor in detail, and we’ll show you how you can replace a bad ABS sensor yourself if you wish.

What Is an ABS Sensor, and What Does It Do?

The ABS sensors in your car work in conjunction with the ABS module to help keep your car stable during braking. In most ABS, there are four sensors, one for each wheel. Since these sensors work by measuring wheel speed, they’re also often referred to as wheel speed sensors.

These sensors work by using a toothed metal ring and a magnet. The toothed ring is attached to the spinning wheel, and as it rotates the teeth repeatedly come into contact with the magnet, which generates an electrical signal. By calculating the frequency at which the ABS module receives these signals, it can determine how fast each wheel is turning.

If you initiate braking and the ABS module senses that the wheels are turning at significantly different speeds, the system will rapidly “pump” the brakes until the wheels are turning at the same speed again. By allowing the wheels to continue rotating ever so slightly while braking on a slippery surface, this stops the wheels from locking up and prevents skidding.

The ABS sensors in your car are also used by your car’s traction control system. Traction control works in much the same way as the ABS, but is used in different circumstances. Specifically, the traction control system activates when you’re accelerating on a slippery surface, as opposed to braking.

If the traction control system detects that your wheels are spinning at different speeds, it will brake individual wheels until everything is spinning at the same speed. Some traction control systems can also stop engine power from reaching a certain wheel if they detect slippage.

What Are the Symptoms of a Bad ABS Sensor?

Unlike some other issues you might have with your car, it can be pretty easy to diagnose a problem with an ABS sensor. Since the input from the ABS sensors only really matters in specific driving situations, you should be able to determine if there’s an issue with your car’s ABS based on how it behaves in certain situations.

Here’s what to look out for if you think that one of your ABS sensors might be acting up:

ABS Warning Light Is On

This is by far the most obvious sign that something is wrong with your ABS. If the ABS light comes on, it indicates that there’s either a problem with one of the sensors, or the ABS module itself.

The ABS warning light is pretty hard to miss; in most cases, this light is just the letters “ABS” displayed in your gauge cluster. Sometimes, the letters may be surrounded by a circle as well, but in either case the ABS light is one of the more straightforward warning lights you have in your vehicle.

Bear in mind, however, that the ABS might not necessarily activate if one of the sensors stops working, depending on what exactly has gone wrong. That’s why it pays to be aware of the other symptoms you might experience from a failed ABS sensor.

Brakes Are Less Effective

As we’ve mentioned, the ABS is designed to activate if it detects skidding as a result of hard braking or braking on a slippery surface. If the ABS fails to activate in these situations, however, then you’ll find braking safely to be much more of a challenge. 

When braking on a slippery surface, you’ll know the ABS is active if you feel the brake pedal pulsing or vibrating beneath your foot. This is because when the ABS pumps the brakes, it sends feedback through the brake pedal.

If you fail to feel the brake pedal pulsing while braking on a slippery surface and it also feels like your car is taking way longer to slow down than it normally does, this is a sign that there is most likely something wrong with the ABS or one of its sensors. 

Read: Causes of Intermittent Hard Brake Pedal

ABS Always Activates When Braking

On the other hand, if your ABS is always activating when you apply the brake pedal regardless of whether your car is skidding or not, this could also indicate a problem with a sensor in the ABS. If an ABS sensor has gone bad, it could be sending an incorrect speed reading to the ABS module and causing the system to activate erroneously.

The ABS should only activate during hard braking or slippery braking, as we’ve previously stated. If it activates in any other circumstances, such as coming to a stop on a clear road from a safe speed, it means something is definitely wrong.

Traction Control Fails to Work

As we know, the ABS sensors are also used to help your car’s traction control system. If one of the sensors stops working, then traction control will be a lot less effective, and you’ll find yourself with a lot less traction than normal when trying to accelerate on a slippery surface.

It’s important that you become familiar with how your car brakes and accelerates when everything is working normally, since this can help you determine more easily if something isn’t working quite as it should be. 

Why Do ABS Sensors Fail?

It’s not terribly rare for ABS sensors to fail, and there are a few common causes as to why this happens. Since ABS sensors are somewhat exposed to the elements, they can sometimes get damaged by dirt and debris from the ground that gets kicked up by the wheels.

Alternatively, the sensors can also be damaged by brake dust and other metallic debris that comes from the car itself.   

Can I Drive With a Bad ABS Sensor?

You can still drive safely with a bad ABS sensor, but it depends a lot on the driving conditions. If you’re driving at safe speeds on dry roads, having a non-functioning ABS ultimately isn’t going to affect your driving experience that much.

On the other hand, if it’s the middle of winter and there’s lots of slush and ice on the roads, driving without a working ABS can put you at a much greater risk of getting into an accident.

Put simply, a bad ABS sensor won’t completely compromise the drivability of your car, but it can make it way sketchier to drive your car in situations where you might not have full traction. If you do discover that one of your ABS sensors isn’t working, you should have it replaced as soon as you’re able to. 

Read: AWD vs FWD – What Are Pros and Cons?

How to Replace Your Car’s ABS Sensor?

First of, we should say that if you don’t have much experience doing this sort of thing, you should probably just take your car into the shop to get a bad ABS sensor replaced. Parts and labor aren’t that expensive for such a repair, plus you would have peace of mind knowing the repair would be done correctly.

If you are confident enough to do this repair on your own, and if you have the requisite tools, here’s what you need to do:

  1. Jack your car up and put it on jack stands, and disconnect the negative cable from the car’s battery.
  2. Find the ABS sensor you want to replace, and disconnect the electrical connector from the sensor’s harness.
  3. Use a ratchet to remove the bolt holding the sensor in place, as well as any other fasteners securing the electrical harness.
  4. Remove the old sensor from your car. Before you throw it away, grab your replacement sensor and compare them, just to double-check that you’re replacing your sensor with the correct one.
  5. Install the new sensor, making sure to secure both the sensor and its harness, if applicable.
  6. Reconnect the electrical connector to the sensor’s harness.
  7. Reconnect the negative cable to the battery, and lower your car back to the ground. 
  8. Take your car for a test drive and see if everything works again. 

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