HELP! Valve cover gasket job by shop now P0400 and P0328

So I noticed oil leaking from the valve covers after slight smoke from engine after parking. I have a 2003 XE with 182,xxx miles on it so I immediately called my reliable and reasonable repair shop and asked if I could drop it off (because I didn't want to drive it while smoking). They confirmed that it was the valve cover gaskets, replaced them, changed the oil, and also "steam cleaned" the engine (so that further leaking would be detected easier). $640 and a day later, I was out the door.

THEN, I got less than 3 miles away and the check engine light comes on... I took it to the nearest autozone and codes P0400 "EGR Function - no/low flow detected" and P0328 "Knock sensor (KS) circuit high input" come up. I did not fill up with new gas in between the repair and the SES light. I plan on calling the shop tomorrow to see if they can take a look (I didn't elude to the fact that I knew what the codes are). The knock sensor is close to the valve covers I believe. Is there a chance that one of the wrench monkeys "knocked" it and it caused a code to show up? Would the valve cover gasket job have anything to do with these codes if something got bumped or did not get re connected? If anyone has any experience or advice, I'd appreciate it. Not sure where to start other than calling the shop of course.

Missing what this place once used to be... I did however get this sorted out. About $2 of hose (free from shop) to the EGR fixed it and both codes are no longer present after 150 miles.