Exhaust Gas Recirculation System
The exhaust gas recirculation (EGR) system is fitted on all vehicles. It comprises of an EGR valve and exhaust manifold to EGR valve tube. The EGR system allows a measured quantity of exhaust gas to be directed back to the intake manifold. The exhaust gas is introduced to the incoming charge in the intake manifold, where it mixes with the air/fuel mixture and lowers the peak gas temperature, reducing nitrogen oxide (NOX) exhaust emissions. The gas is drawn through the exhaust manifold to EGR valve tube from the exhaust to the inlet manifold via the EGR valve. The EGR valve is electrically operated and is controlled via an input from the engine control module (ECM).
The EGR valve is retained on the throttle body elbow.
The ECM can monitor the operation of the EGR system by receiving inputs from the manifold absolute pressure (MAP) sensor. The MAP sensor monitors the EGR flow by the change in intake manifold pressure when the EGR valve is operated. If at any time the input signal to the ECM exceeds pre-defined thresholds due to low pressure reading for a calibrated period of time, a diagnostic trouble code (DTC) is recorded.
The MAP sensor is retained on the side of the throttle body elbow. Refer to Electronic Engine Controls .