EGR System - Gasoline: Description

The exhaust gas recirculation (EGR) system, used on vehicles with gasoline engines, is designed to reduce emissions of oxides of nitrogen (NOx).

This process is accomplished by lowering combustion temperatures of burning gases. Recirculated and metered amounts of exhaust gases are reintroduced into the engine through the intake manifold where they are mixed with the air/fuel mixture.

On some models, the vacuum signal to the EGR valve is controlled by an ECM controlled solenoid valve. The amount of exhaust gas admitted into the engine is then controlled by a vacuum operated EGR valve under all operating conditions.

A thermal vacuum valve (TVV), thermal vacuum switch (TVS) or an electrically operated solenoid controls operating vacuum, depending on engine operating temperature, to maintain good cold driveability.

There are 3 types of EGR systems used, the vacuum modulated (ported vacuum), the exhaust back-pressure modulated, and the pulse width modulated systems. The major difference between the EGR systems is the method used to control how far each valve opens.