do a combination of what everyone said.
disconnect your battery cable for a bit and see if the light goes off, if it goes off then there isn't anything really wrong with the system, mine went on because "bank 1 too lean" basically because i have a CAI
. but if it comes back on in a short amount of time take it to autozone, then when you know why it's on, take it to a mechanic.
my advice is to always do what you can to correct the problem before you have to start paying other people to work on it... personally...