Exhaust Gas Recirculation: Description and Operation

EGR System Diagram:

PURPOSE
The EGR system is used to introduce exhaust gases into the intake to reduce combustion temperatures and NOx emissions.

OPERATION
The ECM operates the EGR valve according to the mapping stored in memory. The ECM controls the duty cycle of the EGR Vacuum Regulator Solenoid Valve which controls vacuum supplied to the EGR valve. The EGR temperature sensor is used to monitor the flow of exhaust gases to verify the operation of the EGR valve. If the temperature sensor signal is out of proper range and/or an electrical failure of the Vacuum Regulator Solenoid Valve is detected by the ECM then a Diagnostic Trouble Code will be stored.

EGR Valve
The EGR valve meters exhaust gas into the intake system. The EGR valve is normally closed. When the system is operating, ported vacuum is applied to the diaphragm chamber of the EGR valve, opening the valve during acceleration and cruising conditions.

EGR Vacuum Regulator Solenoid Valve
A solenoid operated vacuum switching valve is used to regulate the vacuum signal to the EGR valve. The valve is computer operated and works on a duty cycle signal ("ON" time vs. "OFF" time). The valve gets battery power when the ignition is turned "ON" and is energized when the ECM completes the circuit to ground. When the engine reaches normal operating temperature, the ECM begins cycling the solenoid, allowing the EGR system to operate.

EGR Temperature Sensor
The EGR temperature sensor is used to inform the Engine Control Module that the EGR valve is functioning. The sensor monitors the temperature of gases exiting the EGR valve. The EGR temperature sensor is for fault recognition only.