Exhaust Gas RECIRCULATION: Operation: Notes

When EGR Valve receives a vacuum signal from Coolant Temperature Override Switch, valve opens, metering gases from exhaust crossover passage into intake manifold. At 115°F or higher, center and lower ports of CTO switch open (top port is unconnected and not used) and vacuum signal reaches EGR valve. Signals are further regulated by High and Low Temperature Vacuum Modulators. Below 60°F the Low Temperature Vacuum Signal Modulator opens, causing a decrease in amounts of exhaust gases being recycled, or if understood air temperature reaches 115°F, High Temperature Vacuum Signal Modulator opens, and reduction of recirculated exhaust gases also occurs.