The Anti-lock Brake System (ABS) functions by releasing and applying fluid pressure to either the front disc brake calipers or the rear drum brake wheel cylinders during certain braking conditions. The ABS only actuates when one or more wheels approach a slip condition. The ABS automatically senses the slip and activates the fluid pressure control function.
The anti-lock actuator assembly is not used under normal braking conditions. Under normal conditions, fluid from the master cylinder enters the two inlet ports located on the actuator assembly. The fluid then flows through the normally open solenoid valves to each respective wheel location.
The anti-lock wheel speed sensors operate on the magnetic induction principle. As the teeth on the sensor indicator rotate past the stationary sensor, a signal proportional to the speed of rotation is generated and sent via a cable to the control module.
The anti-lock relay is controlled by the control module. The relay is grounded by the control module to power up the system. The control module consists of the fail safe and motor relays. The fail safe relay inhibits solenoid operation and turns the anti-lock brake warning indicator on and off. The motor relay controls pump and motor operation.
The ABS system is operated and monitored by a control module. The control receives readings from the two rear and two front wheel speed sensors and uses this information to compare wheel speeds. Once the control module senses wheel lock-up under a severe braking condition, it sends a pressure reduction signal through the anti-lock relay to the anti-lock actuator assembly. The solenoid controls the flow of hydraulic fluid into a buffer chamber located in the hydraulic anti-lock actuator assembly. This regulates the fluid entering the circuit preventing wheel lock up. When the control module senses the wheel is decelerating it sends a pressure signal through the anti-lock relay to the anti-lock actuator assembly. One signal tells the solenoid to allow hydraulic fluid pressure to increase while the other signal activates the pump motor to further increase pressure by returning fluid from the buffer chamber. This operation continues until all wheels are no longer in lockup.