Description & Operation

The Rear Anti-Lock Brake System II (RABS II) is designed to prevent rear brake lock-up by controlling hydraulic fluid pressure to the rear wheel cylinders. The system consists of 2 warning lights (Red BRAKE and Yellow REAR ANTI-LOCK), a computer module, an electrohydraulic RABS valve, speed sensor and exciter ring.

The control module monitors rear wheel speed continuously. If impending lock-up occurs, the control module energizes the RABS valve. The RABS valve closes an internal isolation valve to prevent rear brake pressure from increasing.

If deceleration is still too great, control module activates dump solenoid. Dump solenoid bleeds rear wheel cylinder fluid into RABS valve accumulator. This allows rear wheels to spin back up to vehicle speed. Dump and Isolation valves will continue to be pulsed in a way that allows rear wheels to rotate, while maintaining maximum deceleration during braking.

The RABS has self-test capability. Red BRAKE warning light indicates low fluid level, parking brake applied. Yellow REAR ANTI-LOCK warning light comes on when control module detects a malfunction and/or anti-lock brake system is inoperative. Both lights should come on for approximately 2 seconds when ignition is turned on or when cranking engine. When Yellow REAR ABS warning light comes on during normal operation, the system has detected a problem and stored a trouble code.