Q: Code po401 replaced everthing

P0401 will often set if the passageway from the EGR valve to the intake is blocked with carbon. If you did not clear that passageway when replacing the EGR valve that is the most likely cause for the code. To clean it effectively, you have to remove the throttle body. In extreme cases, that is if access is difficult or the carbon has become rock hard the intake has to be removed. However, if you use a powerful solvent and appropriate tools you can usually get it clear. If you car is equipped with an EGR temperature sensor, carbon build up on the sensor will also cause that code to set. I would definitely clean the EGR passageways first though. If you desire this service on a mobile basis, simply request a check engine light diagnostic and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.