2002 Lexus ES300 Q&A

2002 Lexus ES300 Question: What happens if the gas cap is not tightened after refueling?

I'm aware that the "Check Engine" light comes on, but why? And if not reset by a mechanic but ignored does this ultimately cause more problems? Does it cause failures with the oxygen sensors, etc.?? -
Answer 2
, uhm....... -