a) Why do people keep expecting people to know the answer to the most vague problems. First port of call if your check engine light comes on, take it to a mechanic, seriously, most of us aren't professionals here and we can't go it's definately this because we're no where near the car. Seriously it could be anything from a faulty signal coming from a random sensor to do with the glove box compartment being open (made up).
b) If you're still determine to DIY fixing it, which you may soon find out you can't (and in which then you'll need to take it to mitsu or a mechanic who will still plug in their OBD scanner, trust me, even though you know the issue they'll still find the issue themselves), you'll still need to get what all of ^^^^^^^^^^^^^^^^^^^^^^^ those guys are talking about.
/rant.
