check engine light code?

well after i put my headers on my check engine light didnt take long to turn on..i soon after bought a datalogger apon everyones request..it told me the code was " p0400 " the datalogger aloud me to turn this light off..but im curious to see what that code means..does anyone have a book or something that will say what that means??? thanks

EGR Flow Malfunction

ya i figured it had to deal with egr...so is that a problem? or just let it go?

only a problem if you need to pass emissions testing.