P0401 You may want to try this
 

I have been fighting the P0401 code and even though my vacuum system worked, ECM solenoid was good and I replaced the EGR valve (non-OEM from AutoZone) I was still getting the code.

I finally assumed the gas flow was restricted and DID NOT want to take the intake off to clean it. I was especially miffed because I had the dealer do the plugs and wires because I was lazy and they didn't clean the manifold when they had it off. Then told me they could clear the code by taking the intake off and cleaning it for $800+. I have a bad opinion of them.

Anyway--the good part. I had been shooting and when cleaning my guns the lightbulb went on. Carbon accumulates from shooting...

So, I got some Hoppes Foaming Cleaner from WalMart for $7, removed the EGR valve and generously foamed both paths to the EGR valve. Then I took my 9mm bore brush on a plastic wand (for flexibility) and scrubbed both sides as far as I could. Yes, it started working. Rinsed with compressed air. Repeat.

After a few times it looked better and by blowing air through both sides it sounded more clear.

Replaced EGR valve and guess what? 300 miles so far and no SES light.

I think it works. Certainly you should try it.

Unorthodox application, but your reasoning is good. Glad it worked for you. Thanks for sharing.

Follow up. It also helps to disconnect the pipe that runs from the exhaust manifold up to the intake at the intake and scrub that area too.