Tell me what you think...

[GmX5]

My check engine light has been on for a couple of weeks (I've been driving my trusty civic). Anyway, I'm tired of driving the civic so I ordered a new gas cap thinking this might be the issue, since gas cap was looking kinda sad anyway. I go to autozone to get the code(s) read and they inform me that auto stores cant read codes in California anymore . So i go down the street to a shop they recommend and make an appointment for 1 1/2 hour later. I put the new gas cap on and drive around for an hour..then go to my appointment. They tell me it read code P0171 (bank one system one lean). I turn on the car and light is gone. I ask the guy if he reset it and he swore he didnt. I know this post is getting lengthy...so here it is...1) could the gas cap have been the problem? 2.) if the problem is still there shouldn't the light come right back on, if so how soon? What are your thoughts? And yes, I did use the search tab..just thought i had a unique situation

Thanks--Gm