EGR Control Solenoid: Description and Operation

EGR Wiring Diagram:

The EGR is controlled by a vacuum solenoid that uses "Pulse Width Modulation." The valve allows the ECM to turn "ON" and "OFF" the solenoid many times a second. The ECM varies the amount of "ON" time (Pulse Width) to change the amount of exhaust gas flow. The Coolant Temperature Sensor (CTS), Throttle Position Sensor (TPS), and PARK/NEUTRAL switch transmit signals to the ECM in order to regulate the EGR solenoid. During cold and idle operations, the solenoid circuit is not grounded by the ECM, which does not allow vacuum to flow to the EGR valve. The amount of exhaust gas flow depends on manifold vacuum and variations in exhaust back pressure.