Your check engine light usually comes on in response to an imbalance in your fuel/air ratio in your exhaust. Usually. You might try running a can of injector cleaner through your gas tank in case you are running lean. How's your performance been? Have you noticed a drop in your average MPG? You can also take your car to an auto parts store and most of the time they can hook their computer to your car and tell you why the light is on for free (but only of the light is on when they hook it up)