Brake Fluid Accumulator: Description and Operation

There are two fluid accumulators in the HCU - one for the primary hydraulic circuit and one for the secondary hydraulic circuit. Each hydraulic circuit uses a 5 cc accumulator.

The fluid accumulators temporarily store brake fluid that is removed from the wheel brakes during an ABS cycle. This stored fluid is used by the pump/motor to provide build pressure for the brake hydraulic system. When the antilock stop is complete, the accumulators are drained by the pump/motor.

On ABS-only vehicles, there is a mini-accumulator on the secondary hydraulic circuit that protects the master cylinder seals during an ABS stop, and there is a noise dampening chamber on the primary circuit.

On ABS with traction control vehicles, there are two noise dampening chambers in the HCU.