EGR System: Operation

Below 102.2°F (39°C), the Electric Vacuum Switching Valve (EVSV) is closed and above 104°F (40°C) the EVSV is open. With EVSV open and throttle valve opening angle positioned below EGR port, EGR vacuum modulator opens passage to atmosphere.

With throttle valve opening angle positioned between EGR port and as exhaust gas pressure increases, EGR vacuum modulator closes passage to atmosphere and EGR valve opens. As exhaust gas pressure decreases, modulator opens passage to atmosphere and EGR valve closes.

With throttle valve opening angle positioned above EGR port, EGR vacuum modulator passage is closed to atmosphere and EGR valve is open. At this stage, the EGR valve remains open because of a negative pressure being applied to the EGR port, even when the modulator opens to the atmosphere.