Description & Operation

The EGR system controls NOx emissions by recirculating exhaust into the combustion chamber through the intake manifold. Exhaust backpressure operates the EGR modulator diaphragm which controls vacuum transmitted to the EGR valve.

Under low load conditions, exhaust pressure is low and a spring pushes the EGR diaphragm down. The modulator valve opens to let outside air into the vacuum passage, lowering the vacuum pressure transmitted to the EGR valve and allowing less exhaust gas to recirculate. Under a high load, the modulator diaphragm is pushed up and the modulator valve closes. Outside air does not enter the vacuum passage and a larger vacuum is transmitted to the EGR valve. The EGR valve opens wider to recirculate a larger amount of exhaust gas to the intake manifold.

When the coolant temperature is low, a Bi-Metallic Vacuum Switching Valve (BVSV) opens the EGR valve vacuum passage to outside air and the EGR valve remains closed.