I have a 2006 Saturn Ion, and a few months ago I started getting a warning about my gas cap. Specifically, as I was driving the dash display would beep and say "Check Gas Cap." I bought a new cap to rule out that issue, and I've been diligent about making sure it's screwed on and clicking to be on tightly.
In spite of that the message still pops up every few days, and will eventually throw a check engine light in response.
I live in an area with emissions testing, so I'm trying to figure out if this is a real problem, or simply that I somehow got another bad gas cap. The cap wasn't specifically a Saturn/GM branded cap, but the computer systems at the auto-parts store indicated it was a part compatible with my car.
Is there any way for me to test if it is indeed the gas cap, or find out with any more certainty what the actual problem is? If I need to take it into a mechanic, will they actually be able to help me, or am I libel to end up paying over and over again for uncertain outcomes?