Exhaust Gas Recirculation: Description and Operation

System Overview
The Exhaust Gas Recirculation (EGR) system is designed to do the following:

- reintroduce exhaust gas into the combustion cycle
- lower combustion temperatures
- reduce the formation of Oxides Of Nitrogen (NOx)

The amount of exhaust gas reintroduced and the timing of the cycle varies by calibration. Timing and volume are controlled by the following:

- engine rpm
- engine vacuum
- exhaust system back pressure
- engine coolant temperature
- throttle position

NOTE: All EGR valves are vacuum-activated, and the vacuum hose routing diagram and EGR system application are shown on the Vehicle Emission Control Information (VECI) decal.

DPFE EGR System Diagram, OBD II:

Differential Pressure Feedback EGR (DPFE)
The EGR system is a differential pressure feedback, subsonic closed loop EGR system, which does the following:

- monitors EGR flow rate by the pressure drop across the metering orifice
- uses an EGR backpressure transducer as the feedback device
- varies controlled pressure valve movement using vacuum output of the EGR vacuum regulator solenoid
- uses the EGR valve only as a pressure regulator, rather than a flow metering device
- allows for a more accurate assessment of EGR flow requirements