EGR System: Description
The Exhaust Gas Recirculation (EGR) system, is designed to reduce oxides of nitrogen (NOx) emissions. This process is accomplished by lowering combustion temperatures of burning gases. A metered amount of exhaust gas is recirculated into the intake manifold and mixed with the air/fuel mixture.
On some models, the Electronic Control Module (ECM) controls EGR valve operation by controlling vacuum to EGR valve. An ECM controlled vacuum solenoid valve is located in series between vacuum source and EGR valve. The ECM uses information from input sensors to determine the correct amount of EGR.
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 5 types of EGR systems used, pulse width modulated, electronic, ported, digital and backpressure (positive and negative) systems.