DESCRIPTION
Anti-Lock Brake System (ABS) consists of speed sensors (on both front rotors and in rear axle), an Electronic Control Unit (ECU) (under left side of instrument panel), and a hydraulic modulator (in engine compartment). See Fig. 1. The hydraulic modulator consists of front and rear pressure control solenoids and relays, a return motor pump and relay, and an ECU connector. Modulator pressure control solenoids are mounted inside hydraulic modulator and are not individually serviceable. Replace modulator assembly if solenoids are defective. An ABS warning light in instrument panel will remain illuminated if an ABS failure occurs. If an ABS malfunction occurs, conventional braking system takes over. Vehicle may be safely driven when ABS warning light is on.
OPERATION
Hydraulic system consists of master cylinder, delivery lines, hydraulic modulator, electric solenoid valves, return delivery pump and brake calipers. Solenoid valves are contained within hydraulic modulator. Individual solenoid valves are used for pressure control to left and right front calipers, while rear brake line pressure is controlled by a common, regulated rear solenoid valve. Hydraulic modulator controls hydraulic pressure to each front brake caliper or both rear calipers independent of pressure produced by brake master cylinder. However, pressure cannot exceed master cylinder pressure.
Download ANTI-LOCK BRAKE SYSTEM 1994 Volvo 960.pdf
