Description & Operation

The Rear Anti-Lock Brake System (RABS) is designed to prevent the 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 2 warning lights, computer module, an electro-hydraulic valve, speed sensor and an exciter ring. See Figure .

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

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