Exhaust Gas Recirculation: Description and Operation

The EGR system returns a small metered amount of engine exhaust gasses to the intake manifold, where it is mixed with incoming air and fuel. This air/fuel/exhaust mixture lowers combustion temperatures, which reduces the formation of oxides of nitrogen (NOx).
Exhaust gas recirculation is controlled by an EGR control valve. The EGR control valve is installed ``in line'' in a passage between the exhaust manifold and the intake manifold. The EGR valve is controlled by a vacuum signal, taken from the intake system. This vacuum signal is modified to control the amount and timing of exhaust gas recirculation by the EGR/canister purge solenoid. When the solenoid is energized by the ECU, it prevents manifold vacuum from acting on the control valve, thereby preventing operation of the EGR system. When the solenoid is deactivated by the ECU, the solenoid opens and allows manifold vacuum to act on the control valve, thereby activating the system accordingly.
EGR operation is restricted during warm-up, idle and wide open throttle operation, and is fully operational during normal cruising modes.