ABS Speed Sensor
If you have ABS brakes than you probably have what is known as an ABS speed sensor, which is also called a speed sensor or even a wheel sensor, depending on who you are talking to. Many people don't even know that they have an ABS speed sensor until it stops functioning correctly and at this point it can cause a wide variety of problems. Because many people don't even know that they have an ABS speed sensor they fail to maintain it properly, in fact this is one of the most widely overlooked maintenance issues with ABS brake systems.
An ABS speed sensor is located on each wheel hub or rotor, although they can be found on the differential housing. Regardless of their location, the ABS speed sensor is what provides information to the ABS computer. This is nice because when you brake, if the wheels are not all equal such as would be the case if your wheels locked up, the computer will use the anti-lock feature until all of the speeds are equal and the vehicle is running at a safe speed.
There are many different types of ABS speed sensors, which is perhaps why there is a lot of misinformation out there about where to find them and how to care for them. There are two different kinds of sensors that fall under what is known as the sensor/ring design and these are the concealed and exposed sensors. In the exposed design the sensor and the sensor ring are exposed, which means they come in contact with brake dust. The sensors are magnetic and the brake dust is metallic, which means many times these sensors stop working properly because they are filled with brake dust.
The concealed design ABS speed sensor is not exposed to the elements, hence its name so it will not need to be cleaned as often, but as a general rule the ABS speed sensor should be cleaned whenever the wheel bearings or the rear differential fluid is being changed out just to make sure that there is not any build up on the sensors that will cause the sensor to stop working or not to work as well as it should. Whether it is on the concealed or the exposed design, build up on the ABS speed sensor is serious as it interferes with how the brake system is supposed to work. At the least you will have an irritating light telling you that the ABS is not engaged and at the most your brakes will not work the way you need them to.
If you're not sure what kind of ABS speed sensor you have on your vehicle all you need to do is remove the brake rotor and look at the backside. If you can see the sensor and the reference ring is visible to the naked eye, you are looking at an exposed ABS speed sensor.
Regardless of the type of ABS speed sensor you have, they should be serviced every time you have your brake pads changed or every 30,000 miles, whichever comes first. By servicing the ABS speed sensor when you are servicing the brakes or every 30,000 miles you will be sure to keep your antilock brake system in good working order at all times. If you neglect to do this you may find that your ABS doesn't work and this may even affect functions such as your cruise control, depending on your vehicle. It just makes sense to service the ABS speed sensor often to avoid these serious and often irritating problems that aren't necessary.
