2nd air injection system.
there is a tube running from manifold to a one way valve, if the computer senses air the wrong way, then it trips the light. They ran 40 bucks each for the valve last time I bought them 2-3 years ago. easy to replace, find a tube running from manifold with a large hex on valve, replace them both, reset light.
I just got mine lit up the other day, scanned it and same thing. they get moisture in them and go bad, rubber one way valve wears out easy. I have 157,000 miles on mine and only replaced them once. I did clean them out once and it helped but it's easier to replace them at that price.
The 2nd air injection shoots cold air into exhaust for emissions, there is a fan that sounds like a hair dryer. It's mounted on the passenger side of the fender area. Also check tubing for leaks and what not.