EGR System: Operation

Exhaust back pressure operates the EGR modulator diaphragm, which controls vacuum transmitted to the EGR valve.

Under low load, 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 vacuum and slightly opening the EGR valve.

Under high load, the modulator diaphragm is pushed up and the modulator valve closes. Air does not enter the vacuum passage, so vacuum to the EGR valve is larger and the EGR valve opens wider.

When coolant temperature is low, the BVSV opens the EGR valve vacuum passage to outside air and the EGR valve remains closed. When coolant temperature is normal, the BVSV is closed and the EGR valve opens and closes in accordance with EGR modulator operation.