Every time you turn your car on, you should see a light on your dash or instrument cluster that says "AB". That is letting you know that the car's ECU just performed a quick check of the anti-lock brake sensors at each wheel to see if they are reporting. If the pass their check, the light is supposed to turn off. If not, then there is trouble with one or more of the sensors. This could spell trouble, since the ABS wheel speed sensors need to know how fast the wheels are turning in order to function properly. If they have excess dirt, grease, or other residue built up around the contact, they may not pick up on the rotation of the wheel hub. If there is a frayed or cut wire, then they may not be able to report at all. Either way, if the ABS sensors can't do their job, then you run the risk of losing control of your vehicle if you apply the brakes at high speeds - something that could be very dangerous on a highway or in the rain. The cause for this problem should be diagnosed right away.
The first anti-lock braking systems were invented not for use on automobiles, but for use on aircraft. It wasn't until the late 1950's that ABS wheel speed sensors were seen on the road, and those were on motorcycles. In the 1970's they found their way to passenger cars, and by the 1990's they were standard equipment. This was a great leap forward in terms of driver safety, and greatly reduced the stopping distance for cars that implemented the new system. That is because anti-lock brake sensors monitor the speed of a vehicle and control its brakes in such a way that they prevent skidding or sliding as a result of trying to stop at high speeds (http://en.wikipedia.org/wiki/Anti-lock_braking_system). Essentially, it is comprised of a controller module, four sensors, and hydraulic valves. The ABS sensors detect the rotational speed of each wheel and will send the signal to the controller. That controller will then respond by using the hydraulic valves to reduce the braking force to a locked wheel ultimately speeding it up.
Changing your ABS speed sensor is very easy. As long as you have a jack, stands, and basic tools you will be able to do it. The most challenging part of the procedure is diagnosing which sensor is bad, and for that you just need an ohmmeter and some time. You will have to remove each sensor at the wheel hub (or differential), unplug it, and test it at the two contacts. When you find the sensor with an anomalous resistance reading, then you will know that's the one that needs replacing. Basically, if the resistance is too low (near zero) then the load isn't drawing any current or there's a short somewhere. If the resistance is too high (infinite or O.L.) then the circuit is open and not continuous. Either way, you will be replacing the ABS sensor that you determined was faulty, and hopefully will be back on your way.
When deciding which ABS wheel sensor to buy, you should consider the manufacturer. At Car Parts Discount, we carry brake parts from the top names in the business; brands that have been producing brake parts and their ancillary electronics for years. Whether you want an original equipment or high quality aftermarket anti-lock brake sensor for your car or truck, we have one for you. So don't waste time or money buying anywhere else - order here today.