Antilock Brake System for Early Subarus:
Half Current (Active):
When the ECU senses that the wheel slip is controlled because the calculated vehicle speed equals the actual vehicle speed, the signal to the magnetic valve is decreased. The check ball to the master cylinder is Closed, and the check ball to the HCU reservoir is Closed. This holds optimal fluid pressure at the wheel cylinder.
Increased brake pedal pressure is held in the master cylinder, and the accumulator stores excess fluid pressure from the HCU plunger pump. This only applies to the hydraulic circuit when half current is applied to the magnetic valve. Other circuits (which may be passive) can function in a normal manner.
Fluid returns to the master cylinder via the check ball opening. Reduced pressure on the F valve opens the check ball, and residual accumulator pressure returns to the master cylinder The plunger pump motor is switched to Off.