The Anti-lock brake system is designed to prevent the driver from losing control of the vehicle during heavy braking conditions. It is not designed to shorten the braking distance contrary to what everyone believes. Its sole purpose is to maintain traction between the tire and the road under severe braking conditions which prevents the driver from losing control of the vehicle when braking and turning at the same time. It does this by regulating brake fluid to each wheel separately through the use of a hydraulic brake motor known as the ABS motor. The wheel speed sensors that are mounted on the hub assembly, spindle or in some cases the differential, send an AC voltage signal to the computer. From there the ABS module or computer can control the amount of brake fluid sent to each wheel using the ABS motor and can then control the amount of braking force applied to each wheel thus reducing accidents. If your ABS light is on and you know the code in the computer, you can go to ALLDATA to get a description and a diagnostic flow chart for your specific code stored in the computer. If you have an ABS light on and would like to chat with a mechanic on line for some insight, click here
The ABS (or Anti lock brake light) can come on for many reasons. The computer turns this light on to warns the driver that the ABS is no longer working which means the ABS will not kick in during hard braking or slipping conditions. The most common reasons the ABS light comes on is a bad wheel speed sensor, bad ABS module, bad ABS motor or a wiring issue. Sometimes the ABS motor or module relay will corrode and go bad preventing the components from getting full battery voltage causing this ABS light to come on.
In this picture, the red brake light has come on along with the ABS light.
Here is a picture of an ABS motor on a 1998 Oldsmobile intrigue. The brake master cylinder is attached to this ABS motor in this particular set up. This is the part of the ABS system that controls the hydraulic fluid to each wheel in order to control the vehicle when braking. This unit is in fact bad causing the ABS light and brake light to illuminate on the dash.
Here is a picture of an ABS wheel speed sensor on a 2008 Toyota Rav4. There is nothing wrong with this sensor and the ABS light nor the brake light is illuminated on this particular vehicle. Just thought I would take a picture and give you an example of an ABS sensor. 🙂