Q: P0401

Hi Mushi. Thanks for writing in today. Sometimes the initial diagnosis based on the error code is not the actual source of the problem. In the case of the P0401, the code indicates that that the engine control module (ECM) detected the engine exhaust gas recirculation (EGR) valve is not flowing enough recirculated exhaust gases when it is commanded to open the flow of gases into the intake manifold. One of the most common causes of this code is that the EGR passages are partly blocked and will not allow enough flow of exhaust gases into the intake manifold. Failure to clean the ports before installing the EGR valve is typically the reason the code comes back the next day.