Brake Fluid Pump: Description and Operation

HYDRAULIC CONTROL UNIT (HCU) PUMP MOTOR ASSEMBLY
The HCU contains 2 Pump Assemblies, one each for the primary and secondary hydraulic circuits. Both pumps are driven by a common electric motor which is part of the Hydraulic Control Unit (HCU). The pumps pick up fluid from the sumps to supply build pressure to the brakes during an Antilock Brake System (ABS) stop. The motor only runs during an ABS stop and is controlled by the Controller Antilock Brakes (CAB) via the Pump/Motor Relay. The Pump/Motor Assembly is not a serviceable item. If it requires service the HCU must be replaced.