Description & Operation

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

Under low load conditions, exhaust backpressure is low. The modulator valve remains open to allow outside air into the vacuum passage. This reduces vacuum transmitted to EGR valve allowing less exhaust gas to recirculate. Under a high load, the modulator diaphragm is pushed up and modulator valve closes. Outside air does not enter vacuum passage and more vacuum is transmitted to EGR valve. EGR valve opens wider to recirculate more exhaust gas to intake manifold.

When coolant temperature is low, or when 5th gear switch is on, or when HAC is on EGR will not open. This is due to vacuum passage being closed by a Bi-Metallic Vacuum Switching Valve (BVSV) or Three-Way Solenoid Valve (TWSV). Other than the above, EGR valve opens and closes in accordance with EGR modulator operation.