Q: My check engine light came on after I filled up my tank with gas. What could be the problem?
A: A loose gas cap can trigger the check engine light to go on. Make sure your gas cap is tight. On some vehicles, you should turn the gas cap until it clicks three times to make sure it is tight. If tightening the gas cap does not make the check engine light turn off and you cannot diagnose the problem, it is a good idea to take your vehicle to a mechanic to make sure there is not a serious engine problem. Or purchase an OBDII Scan Tool to retrieve the diagnostic code.