I took my Honda to the AAA care care center and they removed the intake manifold and cleaned out the EGR ports and replaced all the gaskets. It took 3-4 hours. They reset the codes at that time. I have driven approx 20 miles now and the check engine light has not returned. When the codes were reset in the past the PO401 code would return after only 10-15 miles. So far so good.
Code P0401 - EGR Flow insufficient detected. I replaced the EGR valve, PCV valve, air filter and reset code. The code returned after driving 10 miles. AAA mechanic recommended removing intake manifold and cleaning EGR ports. I have not done this yet but will follow-up if that resolves the issue.
CODE PO401--NOT FIXED YET
Bought new back in January 2002, its been a wonderful almost trouble free vehicle for 240k miles so far. Normal maintenance items replaced as expected, timing belt, batteries & tires, etc. Around 130,000 the SES light came on and the code was for insufficient EGR lift. Replaced the EGR valve and cleaned out the local area where the valve is located. This seemed to fix the issue for another 50,000 miles then the SES came on again with the same EGR issue, replaced valve again but it did not solve the problem, Checked new valve per instructions on net, valve was working fine. Bought the EGR port enlarging tool and tried this solution, still the SES light was bright and engine ran a bit rough. Finally removed the valve and using a carbon removing spray, several cans BTW, and a small but still wire managed to flush out some awful crap. Seems that I got it all out and now no SES light.