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

The exhaust gas recirculation (EGR) valve is controlled by the powertrain control module (PCM). When the valve is opened, the exhaust gas flows from the exhaust manifold to the intake manifold through the EGR system. It is mixed with the air/fuel mixture to be drawn into the combustion chamber to lower peak combustion temperature to reduce NOx.

The EGR flow is inspected as follows. The EGR valve is closed during deceleration with the throttle valve fully closed. Then the PCM fully opens the EGR valve. After a set time, the PCM computes the ratio of the present EGR flow to the normal EGR flow by monitoring the fluctuation of the intake manifold pressure between when the EGR valve is fully opened and when it is fully closed. If the EGR flow rate is lower than normal, a malfunction is detected and a DTC is stored.