DTC P0401: Exhaust Gas Recirculation (EGR) Insufficient Flow: General Description

The exhaust gas recirculation (EGR) system reduces oxides of nitrogen (NOx). NOx is generated by high combustion temperatures. The EGR system lowers peak combustion temperatures by recirculating exhaust gas into the air/fuel mixture, thus reducing NOx. The manifold absolute pressure (MAP) sensor detects the intake manifold pressure (vacuum) and the engine control module (ECM) determines if the amount of exhaust gas recirculation is sufficient. When starting to decelerate with the throttle valve closed, the EGR valve is closed. If the intake manifold pressure changes only slightly while the EGR valve opens fully and closes again within a specified time period, a malfunction is detected and a DTC is stored.