The Light is on because the ABS system for your Anti-Lock Brakes has failed....the Brakes will still work...but the ABS wont...basically if you slam on the brakes... you will lock up your tires as if it were an older model car before ABS came out. The most probable cause is a wheel sensor that "Counts" the notches on the wheel axle near the knuckle has failed. Could just be dirty...mis-adjusted or broken.i would need more details to determine the exact cause. Hope this helps.