The 4-Wheel Anti-lock Brake System (ABS) is an electronically operated, all wheel brake control system. Major components include the vacuum power brake booster, master cylinder, the wheel speed sensors, the Hydraulic Control Unit (HCU), Anti-lock control unit, a relay, and on the AWD Galant, a G sensor.
The system is designed to retard wheel lockup during periods of high wheel slip when braking. Retarding wheel lockup is accomplished by modulating fluid pressure to the wheel brake units. When the control unit detects a variation in voltage across the wheel speed sensors, the ABS is activated. The control unit opens and closes various valves located inside the HCU. These valves, called dump and isolation valves, modulate the hydraulic pressure to the wheels by applying and venting the pressure to the brake fluid circuits.