Check Engine Light - Small leak

[sailorjenny]

06 Convert mustang.

Few months ago my engine light went on. Took it to autozone, the lady said tighten the gas cap, then she sent me on my way. It took about a week before the light turned off.

Fast foward to a couple weeks ago, the light came back on. I had my friend run a test on it, he ran a PO456. Took it back to the shop I had repairs done on it last, the guy checked out the engine and then checked the gascap. It wasn't clicking right, so he suggested I get a replacement. Done. Got ripped by the dealership and spend 35 on a new gas cap, put her on, two days later the check engine light is still on.

So I'm guessing its time to check the engine. Anyone have experience with this?