Hydraulic Control Assembly - Antilock Brakes: Description and Operation

The Hydraulic Control Unit (HCU) consists of a valve body assembly, pump, motor assembly and brake fluid reservoir with fluid lever indicator assembly. During normal braking, fluid from master cylinder enters the HCU through two inlet ports at the rear of the HCU. The fluid passes through four normally open inlet valves, one to each wheel. When the Anti-Lock Brake System (ABS) module senses wheel lock conditions, it produces a pulse to the appropriate inlet valve, which then closes the valve. This prevents any more fluid from entering the affected brake. The ABS module senses the wheel again. If the wheel is still decelerating, the module then pulses open the normally closed valve, which decreases the pressure trapped inline.