Anti-Lock Brake System: Operation
When the ignition is turn on, the ECM is activated. Electrical circuits within the ECM activates the system and provides a self-diagnosis on the system. The indicator lights, located on the instrument panel will illuminate, until self-diagnosis is complete. If system has no faults, lights will go off.
If system has detected a fault, one or both lights will stay on to indicate a problem has been detected. With ignition on and vehicle stationary, solenoids within the pressure modulator will temporarily be activated to ensure proper operation.
Pump/motor assembly will cycle on and off to ensure pressure within the accumulator is 1650-2050 psi (11,376-14,135 kPa). If pressure drops below 1050 psi (7240 kPa), a pressure switch located on accumulator block, will signal the ECM to deactivate the ABS system. At this time, Yellow indicator light will come on. The accumulator contains enough pressure to help assist stopping approximately 25-30 times.
With vehicle moving, ECM monitors wheel speed sensor by AC signals from each of the wheel speed sensors. When the ECM receives a signal from the brake switch that braking is taking place, it starts monitoring the rate of deceleration from the wheel speed sensors.
Using this information, the ECM calculates the rate of deceleration to increase, decrease or maintain hydraulic pressure to the wheels. Pressure changes are performed inside the pressure modulators by cycling (opening and closing) the solenoids (one for each front wheels or one for both rear wheels) quickly.