Exhaust Gas RECIRCULATION: Operation

Below a predetermined temperature, when engine coolant is not warm, no exhaust gas recirculation will occur since the thermal vacuum switch is closed. Once coolant warms up, the thermal vacuum switch opens and exhaust gas recirculation is then controlled by the other components of the system.

Vacuum modulator reacts to exhaust back pressure and balances atmospheric pressure and vacuum pressure to allow or stop EGR. Vacuum control valve senses changes in intake manifold vacuum levels and will bleed off or allow vacuum to the EGR valve. The EGR cooler assists in reducing exhaust gas temperature before it is cycled into combustion chamber. This helps further reduce high temperatures which cause NOx formation.