Exhaust Gas Recirculation: Description and Operation

The Exhaust Gas Recirculation (EGR) system is designed to reintroduce a small amount of exhaust gas into the combustion cycle. This exhaust gas acts as an inert gas; that is, it will not burn. This cools the overall combustion temperature. Cooler combustion temperature prevents the formation of Nitrogen Oxide (NOx).

The amount of recirculated exhaust gas is controlled by the Powertrain Control Module (PCM) and is dependent upon:
- Engine rpm.
- Intake vacuum.
- Exhaust back pressure.
- Engine coolant temperature.
- Throttle position.