Usually not urgent, gas cap 1st, and yes advance Auto or similar will diagnose for free. Likely just a sensor.
It could be a variety of issues. Since you're traveling it would be wise for you to stop by Harry's and have them check your vehicle. They are extremely professional and helpful at Harry's and you will find that they may not even charge you. It's best to be safe than sorry. Ask for Michael.
Check gas cap is on tight first
Good idea to check gas cap. You could stop by an Advance Auto or another parts store. Some of them have a device to check your computer to see what the problem could be.
Check your gas cap and make sure it is tight
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