Anti-Lock Brake System: Operation

As vehicle is moving, each wheel speed sensor sends an AC signal to the ECU. When brake pedal is applied, ECU receives signal through stoplight switch. When this occurs, ECU will monitor deceleration rate of wheels through wheel speed sensors. One sensor is located on each wheel.

If deceleration rate from any speed sensor reaches a preprogrammed rate, ECU activates solenoid valves inside actuator (electro-hydraulic unit). Solenoid valves are cycled to apply, release or maintain hydraulic pressure to each brake caliper or wheel cylinder depending upon signals from ECU. Regulating hydraulic pressure to each caliper prevents wheel lock-up.

When brake pedal is released, ECU will deactivate solenoid valves, and system will return to conventional brake system operation until ABS is again needed.

If ECU detects a fault, ANTI-LOCK warning light on the instrument cluster comes on. ECU deactivates ABS when a fault is detected, but conventional brake system is not affected.