The Anti-Lock Braking System (ABS) prevents tires from skidding during hard stops. When a driver slams on the brakes, the wheels can lock up, sliding across the pavement. A skidding tire has no steering traction. ABS uses sensors at each wheel to monitor speed. If a sensor reports a wheel has stopped turning, the ABS computer pulses the brake hydraulic valves to that wheel, releasing and restoring pressure rapidly. This keeps the tire rolling at the limit of traction.
Keeping tires rolling allows the driver to steer around obstacles while stopping. ABS does not always shorten stopping distances, especially on loose gravel or snow, but it keeps the vehicle stable. If the system fails, the ABS dashboard light will turn on, and the car returns to standard power brakes.