Check Engine Light?

My truck is brand new I bought it in Aug. of 03 and it only has 1700 miles and I just got my oil changed at the dealer and had my 3rd door fixed the week before x-mas. Well today I started my truck and the damn check engine light was on so I thought on maby it was just a one time deal so I turned it off and back on again. And it was on again so I go on driving and its still on and has been on since 2pm today. I checked my gas cap to make sure it was on tight because I have herd about if its not on right it will cause the light to come on. Dose anyone know of any other things that are minor that may cause it to turn on? I need to know so I dont have to wake up early tomorrow and go to the dealership.