Check engine light has come on and don't know what the problem is?

This use to happen to me a lot when I had Jeel Cherokee ~Grand. I read in the manual and my mechanic confirmed that it is caused from a loose gas cap and/or I believe the O2 sensor due to the gas cap not being tight. I honestly never fixed the problem because it was really nothing to be concerned about unless you live in the wonderful state of Massachusetts and need a inspection sticker. If you live where vehicle inspection stickers are required then just make sure to go to the garage when the engine light is not on or your local mechanic can hook some electronic diagnostic device/computer and somehow have it turn the check engine light off. Advice, if you have that done go quickly to the garage to get the sticker. Just so you know, I'm not a mechanic but just have experienced this many times over the years and it happened to other vehicles I had. So, I would make sure you talk to a professional just to make sure it's from the gas cap being loose, which I was told by my mechanic and read in the manual.