The Anti-Lock Braking (ABS) control unit is made up of three parts, a pump that builds pressure in the brake lines when called upon, a block to which the brake lines are connected, and a module that controls ABS function. Sometimes called an “ABS block” or “ABS pump”, this unit responds to signals from the wheel speed sensors when they detect that a tire has lost traction.
Without ABS, when your tires lock up during hard braking (or braking on water, snow, or loose gravel), they begin to skid, and they lose their ability to steer in one direction or another. Your vehicle skids forwards - and sometimes slides sideways.
ABS prevents your tires from locking up in those conditions. When a wheel speed sensor detects that a tire has stopped rotating (and is about to skid), it alerts the ABS control unit, which then pulses pressure to the brake pads to slow the wheel down without stopping it completely. In the process, the tire maintains more surface contact with the road and allows you to continue to steer your vehicle. ABS also helps to prevent your vehicle from entering into a dangerous sideways skid or slide.