Exhaust Gas Recirculation System
Exhaust Gas Recirculation (EGR) System Diagram:
The Exhaust Gas Recirculation (EGR) system recirculates a portion of the exhaust gases into the intake manifold under average vehicle driving conditions to reduce combustion temperatures and exhaust gas NOx content. The amount of exhaust gas recirculated varies according to operating conditions and will be cut completely under:
- Engine starting condition
- Low engine coolant temperature condition
- Excessively high engine coolant temperature condition
- Engine idling condition
- High engine speed condition
- Mass air flow sensor failure
The EGR system uses the EGR vacuum regulator solenoid valve to provide vacuum to the EGR valve when commanded by the Powertrain Control Module (PCM). If the exhaust backpressure is sufficient to close the EGR modulator valve, vacuum is sent to the EGR valve and allows EGR gas to flow into the intake manifold. If the exhaust backpressure is not sufficient, the EGR modulator will remain open and allow vacuum from the EGR vacuum regulator solenoid valve to vent to the atmosphere.
The EGR system monitor, for OBD II regulations, uses an EGR temperature sensor to monitor the EGR system. The EGR temperature sensor is a thermistor located in the EGR passageway. When hot exhaust gas is recirculated into the engine, the temperature at the EGR passageway increases. This increase is sensed by the EGR temperature sensor and a signal is sent to the PCM to indicate EGR flow. If the EGR temperature sensor does not detect EGR flow when commanded by the PCM after two consecutive trips, the Malfunction Indicator Lamp (MIL) will be illuminated and a Diagnostic Trouble Code (DTC) will be stored. The MIL will be turned off after three consecutive trips are completed with no faults detected. The DTC will remain stored in the PCM memory until 80 trips have been completed without the same fault detected in the system.
Exhaust Gas Recirculation Modulator Valve
The Exhaust Gas Recirculation (EGR) modulator valve is used to control EGR. The EGR valve is operated by ported vacuum, but the ported vacuum will normally be vented off at the EGR modulator valve. As engine RPM increases, exhaust pressure increases and pushes on the diaphragm in the EGR modulator valve and closes the vacuum vent.
Exhaust Gas Recirculation Vacuum Regulator Solenoid Valve
The Exhaust Gas Recirculation (EGR) vacuum regulator solenoid valve is controlled by the Powertrain Control Module (PCM). The EGR vacuum regulator solenoid valve controls vacuum to the EGR valve. When the EGR vacuum regulator solenoid valve is off (ground signal OFF from the PCM) vacuum is supplied to the EGR valve. When the EGR vacuum regulator solenoid valve is ON (ground supplied by PCM), vacuum is turned OFF keeping the EGR valve closed. The PCM will command the EGR vacuum regulator solenoid valve ON at:
- Engine starting condition
- Low engine coolant temperature condition
- Excessively high engine coolant temperature condition
- Engine idling condition
- High engine speed condition
- Mass air flow sensor failure
EGR Temperature Sensor:
Exhaust Gas Recirculation Temperature Sensor
The Exhaust Gas Recirculation (EGR) temperature sensor is a thermistor type sensor that monitors the temperature of the exhaust in the EGR passageway. As the EGR flow increases, the temperature increases. This process creates a change in the resistance of the sensor, which decreases as the temperature increases. The signal is sent to the Powertrain Control Module (PCM) to indicate that the EGR system is working properly. If the EGR temperature sensor does not change resistance as the PCM expects on two consecutive trips, the Malfunction Indicator Lamp (MIL) will be illuminated and a Diagnostic Trouble Code (DTC) will be stored.
EGR Valve:
Exhaust Gas Recirculation Valve
The Exhaust Gas Recirculation (EGR) valve recirculates portions of the exhaust gas back into the intake manifold to reduce the amount of the NOx released during combustion and to reduce combustion temperature. The amount of exhaust gases that are released into the engine is proportional to the load on the engine.