Exhaust Gas Recirculation (EGR) Systems

The EGR system controls the NOX emissions. Small amounts of exhaust gases are recirculated back into the combustion chamber to mix with the air to fuel charge. The combustion chamber temperature is reduced, lowering NOX emissions

The electric EGR system consists of an electric motor EGR valve integrated assembly, a MAP sensor, PCM, and connecting wiring.

Operation of the system is as follows.

• The electric EGR system receives signals from the ECT or CHT sensor, TP sensor, MAF sensor (if equipped), 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 electric EGR system is activated. The PCM deactivates the EGR during idle, extended wide open throttle (WOT), or whenever a concern is detected in an EGR component or EGR required input.

• The PCM calculates the desired amount of EGR for a given set of engine operating conditions.

• The PCM in turn outputs signals to control the electric EGR motor to move (advance or retract) a calibrated number of discrete steps. The electric stepper motor directly actuates the EGR valve, independent of engine vacuum. The electric EGR valve is commanded from 0 to 52 discrete steps to get the EGR valve from a fully closed to a fully open position. The position of the EGR valve determines the EGR flow.

• A MAP sensor measures variations in manifold pressure as EGR is introduced into the intake manifold. Variations in EGR being used correlate to the MAP signal (increasing EGR increases manifold pressure values).