Hydraulic Control Assembly - Antilock Brakes: Description and Operation

The hydraulic control unit (HCU) is located on the front lefthand side of the engine compartment. It 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 ABS module (electronic control unit (ECU)) senses wheel lock conditions, the ABS module (ECU) produces a pulse to appropriate inlet valve which closes that valve. This prevents any more fluid from entering affected brake. The ABS module (ECU) senses the wheel again, if the wheel is still decelerating the ABS module (ECU) then pulses open the normally closed valve which decreases pressure trapped inline.