The OBDII fault code P0401 means that the engine computer has detected that the Exhaust Gas Recirculation (EGR) system flow is insufficient. This is caused by hot exhaust gas coming into contact with cool intake manifold air and condensing into this muck. The first pic shows the intake manifold aperture where the exhaust gas is meant to re-enter the combustion cycle. The second pic is the EGR valve,(now partially cleaned up), responsible for setting the code. A thorough cleaning and system all happy again!