Exhaust Gas Recirculation: Description and Operation
EGR SYSTEM OVERVIEWThe Exhaust Gas Recirculation (EGR) system returns a small amount of exhaust gas into the intake manifold. This reduces the overall combustion temperature. Cooler combustion temperatures provide a significant reduction of the oxides of nitrogen (NOx) in the exhaust emissions.
The engine incorporates a stepper motor-controlled EGR valve which receives its signal from the PCM. Engine coolant is used to cool the EGR valve. The EGR valve and stepper motor are serviced as an assembly.
The amount of recirculated exhaust gas depends on:
- engine rpm.
- intake manifold vacuum.
- exhaust backpressure.
- engine coolant temperature.
- throttle position.
ELECTRIC EGR (EEGR) SYSTEM
- The EEGR valve is activated by an electric stepper motor and does not use vacuum to control the physical movement of the valve.
- No DPFE sensor is used.
- No orifice tube/assembly is used.
- A manifold absolute pressure (MAP) sensor.
- Engine coolant is routed through the EEGR assembly extending the durability of the electric motor.
EEGR SYSTEM OPERATION
- The EEGR system receives signals from the cylinder head temperature (CHT) sensor, the throttle position (TP) sensor, the mass air flow (MAF) sensor, the crankshaft position (CKP) sensor and the MAP sensor to provide information on engine operating conditions to the PCM. The engine must be warm, stable, and running at a moderate load and RPM before the EEGR system is activated. The PCM deactivates the EEGR during idle, extended wide open throttle (WOT), or whenever a failure detected in an EEGR component or an EGR required input.
- The PCM calculates the desired amount of EGR for a given set of engine operating conditions.
- The PCM outputs signals to the EEGR motor to move (advance or retract) a calibrated number of discrete steps. The electric stepper motor directly actuates the EEGR valve independent of engine vacuum. The EEGR valve is commanded from 0 to 52 discrete steps to get the EGR valve from a fully closed to fully open position. The position of the EGR valve determines the EGR flow.
EEGR VALVE
The EEGR valve is a water-cooled motor/valve assembly. The motor is commanded to move in 52 discrete steps as it acts directly on the EEGR valve. The position of the valve determines the rate of EGR. The built-in spring works to close the valve against the motor opening force.
