Exhaust Gas Recirculation
The Exhaust Gas Recirculation (EGR) system is designed to reduce oxides of nitrogen (NOx) emissions by lowering combustion temperatures. a metered amount of exhaust gas is recalculated into the intake manifold and mixed with the air/fuel mixture.
Early EGR systems components include an EGR Valve, an Engine Control Module (ECM) Controlled Vacuum Switch Valve or EGR Solenoid, and an EGR Vacuum Modulator. Depending on the engine and driving conditions, the ECM will control the EGR Solenoid which will operate the EGR Vacuum Modulator to regulate the opening and closing of the EGR Valve.
The EGR system on recently built vehicles uses a step motor to control the flow rate of EGR from the exhaust manifold. This motor has four winding phases. It operates according to the output pulse signal of the ECM. Two windings are turned ON and OFF in sequence. Each time an ON pulse is issued, the valve opens or closes, changing the flow rate. When no change in the flow rate is needed, the ECM does not issue the pulse signal. A certain voltage signal is issued so that the valve remains at that particular opening.