I have a repair code P1404 on my 2001 oldsmobile sihouette. It has to do with the emissions system, what would be the first items to check

Check the EGR Valve--carbon may have built-up on the pintle valve. Start using only full-synthetic 5W-30 engine oil. This will keep the emissions system much cleaner. Change oil and filter every 6,000 miles or 6 months, whichever comes first.

Replace your EGR valve.