The air injection system is used for emissions, it shoots air prior to the catalyst converter so it helps burn up easier. My car has the check engine light on too and my girlfriend (a mechanic) scanned it and it came up too. We plan on replacing it ourselves as we they say we are out of the 3/36 bumper to bumper warrenty. It's not hard at all, your dealership should be able to handle it. There's a nifty service manual someone has uploaded on this site that you can download and see for yourself what parts are involved and how to replace it.