So about an hour ago, I got out of class and walked to my car, turned on the engine and the Service Engine Soon light came on.

It wasn't on when I turned off the engine this morning after driving to class, and I haven't filled up any gas since Saturday or Sunday so I don't think it's the gas cap. I did open and closed it again to make sure. Any other ideas as to what it could be? Something simple?

I'm just hoping it's nothing big and I don't have anytime to take it to the stealership yet. I haven't noticed any performance issues....