Exhaust Gas Recirculation: Description and Operation
EXHAUST GAS RECIRCULATION (EGR) SYSTEM OVERVIEWPURPOSE
The exhaust gas recirculation system recirculates a portion of the exhaust gases into the intake manifold under average vehicle driving conditions to reduce combustion temperatures and exhaust gas Oxides Of Nitrogen (NOx) content. The amount of exhaust gas recirculated varies from zero, with a cold engine, to a fixed rate for a hot engine with intermediate load and low engine speed. The exhaust gas flow rate increases steadily as coolant temperature rises above 65°C (150°F).
COMPONENTS
The system uses a control solenoid, activated by the PCM, to control the EGR valve. The components that affect the EGR system are:
- Camshaft Position (CMP) sensor.
- EGR vacuum regulator solenoid.
- EGR Temperature (EGRT) sensor.
- EGR valve.
- Engine Coolant Temperature (ECT) sensor.
- Mass Air Flow (MAF) sensor.
- PCM.
- Throttle Position (TP) sensor.
OPERATION
The EGR system can be deactivated, aside from component malfunction, by the PCM and sensor inputs to the PCM. To deactivate the EGR system, the vacuum supply to the EGR valve is eliminated. The PCM activates the EGR vacuum regulator solenoid to disable the EGR system.
The solenoid controls the EGR valve by controlling vacuum supply to the EGR modulator valve. If the PCM and the sensor inputs determine the EGR valve needs to be closed, the PCM activates the EGR vacuum regulator solenoid. When activated, the EGR vacuum regulator solenoid vents vacuum to the atmosphere so that the EGR valve remains closed.
An EGRT sensor is threaded into the bottom of the upper intake manifold. The EGRT sensor detects the EGR flow and notifies the PCM with an input signal. The PCM can then determine the EGR valve position and regulate the EGR valve.
Additionally, the EGR modulator valve monitors exhaust back pressure to control vacuum to the EGR valve. When exhaust back pressure is too low, vacuum is cut off to the EGR valve.