Exhaust Gas Recirculation: Description and Operation

Exhaust Gas Recirculation Component Layout:

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 FREQUENCY 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 Engine Control Module (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:

EGR TEMPERATURE SENSOR
The EGR temperature sensor is used to inform the Motronic 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.