Description & Operation

The Rear Anti-Lock Brake System (RABS) is designed to prevent vehicle from skidding due to rear brake lock up. This is done by controlling the amount of hydraulic fluid pressure to the rear wheel cylinders. The system consists of a warning light, computer module, an electro-hydraulic valve, speed sensor and a excitor ring. See Fig 1 .

As vehicle is moving, speed sensor mounted on rear axle signals the computer module. This is done by the speed sensor generating an AC frequency signal as the teeth on exciter ring, located on differential case, passes by the speed sensor probe. When the brake pedal is depressed, control module senses drop in vehicle speed.

If rate of deceleration indicates lock-up is occurring, the control module activates the electro-hydraulic valve which closes the internal isolation valve. If speed sensor signal still indicates lock-up occurrence, the control module activates the dump solenoid which bleeds off brake fluid pressure. When the control module determines that lock-up condition no longer exists, all valves and solenoids open allow brake system to return to normal operation.