What is an antilock brake system (ABS)?

The purpose of the antilock brake system is to prevent the wheels from locking up or skidding during braking.  If the brakes lock up, the vehicle takes longer to stop, and the ability to steer the vehicle is greatly diminished.  The ABS system prevents wheel lock-up by monitoring each wheel with a wheel speed sensor.  When the wheel starts to skid, hydraulic pressure to the brake is temporarily reduced to prevent the wheel from skidding.