Electronic Brake Control Systems - Electronic Skid Control: Operation: Notes
During normal driving conditions, AC voltage is sent by wheel sensors to controller. When controller is not sensing an impending wheel lock-up, modulator vacuum solenoid is without ground circuit and normal brake pressure is transmitted to rear wheel cylinders (see illustration). When controller senses an impending wheel lock-up, an electrical signal is sent to energize solenoid and create a sealed hydraulic circuit between check valve and rear wheel cylinders. Modulator displacement piston moves slightly to increase rear brake line volume resulting in a decrease in pressure to the rear wheel cylinders and alleviating lock-up tendency (see illustration ). During a maximum braking stop, solenoid valve will continue to cycle, alternately supplying air or vacuum to modulator, until vehicle speed is less than five miles per hour or until brakes are released by driver.