Engine Emission Control: EGR: Notes
WARNING: This page is about a different car, the 2009 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.
The EGR system returns a small amount of exhaust gas into the intake manifold. This reduces the overall combustion temperature. Cooler combustion temperatures provide a significant reduction of the Nitrogen Oxides (NOX) in the exhaust emissions.