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

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.??

by in Houston, TX on June 14, 2014
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2 answers
ANSWER by , June 14, 2014
No !
ANSWER by , June 14, 2014
, uhm.......