Anti-lock Braking System. A safety feature in most modern cars, it is a computerized braking assist system which senses when one or more wheels are close to locking up and skidding, resulting in a loss of braking and steering control. Using sensors at each wheel (or in some cases in the differential gear housing), an ABS computer keeps track of any sudden deceleration at any given wheel, and controls the ABS valves and pump to alternate brake line pressure.If you’ve ever panic-stopped in an ABS-equipped vehicle, you’ve likely felt this alternating pressure in the brake pedal.