Anti-Lock Brake System: Operation

As vehicle is moving, speed sensors send an AC signal to ABS control unit. Control unit monitors brakelight switch to determine when brake pedal is pressed. When brake pedal is pressed, ABS control unit monitors signals from each speed sensor to determine rate of deceleration.

On 4WD models, "G" sensor is used to determine whether vehicle is being driven on high or low friction surfaces. An internal reed switch is magnetically turned on during normal conditions. During hard braking on high friction surfaces, internal magnet moves to front of sensor and removes magnetic field from reed switch allowing it to turn off.

If rate of deceleration from any speed sensor reaches a preprogrammed rate, ABS control unit activates solenoid valves inside actuator. Solenoid valves are cycled to apply, release or maintain hydraulic pressure to each wheel in any combination.

Regulating hydraulic pressure to each circuit prevents wheel lock-up. When brake pedal is released, ABS control unit deactivates solenoid valves, returning brake system to conventional mode until ABS is needed.

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