Assuming there is no problem, disconnect the battery. Reconnect it after atleast 3 minutes, so the computer has time to clear out. If the light comes back on, you got a problem. You can bend a paperclip into a 'U' shape, and insert it into the bottom right two holes on the diagnostic hook-up. This will make your check engine light flash. Each series of flash is a part of the code to what is wrong with your vehicle. Then, look up the code in a Chilton's or Hayes Vehicle Book (specific to your vehicle, of course) to reference the problem. This takes time, but costs you absolutely nothing, which is a price I love to pay.