California Models

DPFE EGR System Diagram, OBD II:

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 nitrous oxide (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

The EGR valve is vacuum-activated, and the vacuum hose routing diagram is shown on the vehicle emission control information (VECI) decal.

Configuration

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