What is troubleshooting code P0401?

P0401 = Insufficient EGR Flow My '97 Lumina failed state inspection because of this. No fix yet... for big list of codes see: http://www.obdii.com/ubb/Forum1/HTML/002126.html

good website there...but the codes are manufacturer specific, so we can't help you troubleshoot unless we know your car. for a egr problem, start with the dpfe sensor. next clean out all passageways. on my Ford i took off the throttle body and found the clog in the c-shaped passage ont he face of the intake manifold.

good luck,

mb