My daughter in law brought her car to me about the check engine light being on the other day, so I hooked up the code reader and got PO401 EGR Flow Insufficient Detected. I took the EGR valve off and cleaned it and cleaned the EGR port on the intake manifold and put it back together and it solved the problem. I just wanted to post this in case anyone else ever gets this code, but be sure you also clean the port in the intake. Her car has a port about the size of the end of my smallest finger and was nearly completely stopped up. The auto parts store had told her she needed a new EGR valve. WRONG!!!