Anti-Lock Brake System: Description

Anti-Lock Brake System (ABS) is designed to prevent wheel lock-up during heavy braking. ABS electronically controls brake fluid pressure, reducing chance of wheel lock-up. This allows driver to maintain better steering control of the vehicle. ABS system consists of 4 wheel speed sensors, 4 tone rings, ABS Electronic Control Unit (ECU), hydraulic control unit, "G" sensor (Legacy 4WD M/T) and ABS warning light. See Figure and Figure .

Two types of hydraulic control units are used. One is manufactured by Bosch; the other is manufactured by Nippon under license from Bosch. The Nippon unit has "F" Valve to prevent brake pedal pulsation when brake fluid pressure decreases.