Anti-lock Braking System (ABS)
What it is: Anti-Lock Braking Systems are designed to keep the wheels from locking up during hard braking, or during normal braking on slippery surfaces. First and foremost, this helps the driver retain steering control; in some situations, ABS can also help shorten stopping distances.
How it works: A microprocessor or control unit continually compares the rotational speed of the wheels via electronic sensors located at each wheel. During braking, if the control unit determines that one of the wheels has locked up, it directs an ABS hydraulic system to individually and rapidly "pump" that brake until its rotational speed is back in line with the other wheels.
What it feels like: The feel of ABS actuation varies from vehicle to vehicle, but it typically is felt through a pulsing action through the brake pedal, and may include the sound of the hydraulic pump working. This is normal, and the driver should maintain steady pressure on the brake pedal (without "pumping" the pedal) until the vehicle has slowed sufficiently to be out of danger.
How it benefits the driver: ABS can help the driver avoid an accident by enabling him or her to steer out of trouble in an emergency-braking maneuver, or to maintain directional control during normal braking on a slippery surface.