Anti-Lock Valve (ALV)

ALV, located on right frame rail, contains an isolation valve, dump valve and accumulator. Isolation valve is normally open, and fluid will flow through valve during normal operation. Dump valve is normally closed, and accumulator is normally empty.

When anti-lock brake system is activated, ECM closes isolation valve. If closing of isolation valve is insufficient to prevent wheel lock-up, ECM will open dump valve, allowing brake fluid to flow into accumulator. This reduces hydraulic brake pressure to prevent wheel lock-up.

If wheel lock-up still exists, ECM opens dump valve again, allowing hydraulic brake pressure to decrease. This procedure will be repeated until hydraulic brake pressure is reduced and proper wheel speed is obtained. When brake pedal is released, isolation valve is de-energized, brake fluid in accumulator returns to master cylinder and normal brake operation exists.