ABS Modulator
The ABS modulator consists of the inlet solenoid valve, outlet solenoid valve, reservoir, pump, and the pump motor. The modulator reduces the caliper fluid pressure directly. It is a circulating-type modulator because the brake fluid circulates through the caliper, reservoir, and the master cylinder. The hydraulic control has three modes: Normal braking, pressure retaining, and pressure reducing. The hydraulic circuit is an independent four channel type, one channel for each wheel.
Shown in Normal Braking Mode

Normal braking mode: | Inlet valve open, outlet valve closed: Master cylinder fluid is pumped out to the caliper.
Pressure retaining mode: | Inlet valve closed, outlet valve closed: Caliper fluid is retained by the inlet valve and outlet valve.
Pressure reducing mode: | Inlet valve closed, outlet valve open: Caliper fluid flows through the outlet valve to the reservoir. When in pressure reducing mode, the pump motor is ON. The reservoir fluid is pumped out by the pump, through the damping chamber, to the master cylinder. When stopping ABS operation, the pump motor is OFF.