No gas cap

I don't have a gas cap on my car.. is this a problem?

i dont know if thats a problem or not but if you think theres a problem you can always by a new one

many cars, civic being one of them require a certain amount of pressure in the fuel tank to help push the fuel to the engine, that's why when you open your gas cap, you hear the sound of air escaping, so yes, you need a gas cap. plus, it prevents things like water and dirt from getting in your tank

your engine light might come on because of the lack of pressure, and crap can get in the tank easier. thats all i can think of that could happen.

That happens to my mother's CRV. If the gas cap isn't tight enough, the check engine light will come on. Very annoying.

If the check engine light(1998&newer) does come due to a missing or loose cap then it will reset itself aftre a few weeks. It all depends on how much you drive/how you drive - the owners manual says something like 2-3 trips.

If its missing, just replace it. Some states you WILL NOT pass an emmisions inspection with it missing.