The vast majority of modern vehicles are equipped with anti-lock brake systems (ABS), which are supposed to improve safety when it comes to extreme braking situations. Whether the driver in front of you stops short or you hit a patch of ice, the ABS unit will take control and pump the brakes to help the wheels find traction and come to a stop.
Basically, when a driver slams on the brakes but the wheels are still in motion, a sensor will alert the ABS computer so it can take over and stop the car safely. Every time you start your car, the ABS computer runs a quick diagnostic check to make sure everything is working properly before you set out on your drive. If it senses that something is wrong, it will trigger a warning light to illuminate on the dash.
An ABS warning light could be on for a number of reasons, but this does not mean that your every-day brakes are malfunctioning. However, ABS does rely on the regular brakes to function properly, so if the regular brake warning light is on, it may be the reason the ABS light was triggered. Barring that scenario, there are a few reasons an ABS warning light may have been triggered.
First, try to turn the car on and off. There may have simply been a misdiagnosis when the ABS computer ran its preliminary diagnostic test. If it comes on again, a diagnostic test can be performed on the ABS controller with a scan tool, and the code readout can point you in the direction of the problem.
Check the fuse that correlates to the ABS controller. A burnt out fuse will require simple replacement, which ought to get things back in order and cause the light to turn off.
After you've checked the basic fixes, the next step is to visually inspect the ABS controller, the wires and the harness for signs of damage and corrosion. Even a minor scratch can disrupt the flow of volts enough to affect the ABS readings and alert the system that there is a problem. Things like water, dirt and other debris that get into the underbelly of the vehicle can damage the wiring of the ABS.