Go to Ebay
and buy yourself an OBD2 code reader.
Most places, you can go to AutoZone or Advance Auto and get them to read your codes, but Pascal informs me that his local Autozone has ceased doing this.
If I have to guess, I’m guessing that the dealerships lobbied to make the stores stop the practice of reading/resetting codes for free, and this is probably coming to a store near you.
You can buy a code reader for well under a hundred bucks. You can buy an app for your android that will do the same thing for not much, too. And a bluetooth adapter that you can leave in the car. Get it before they make that illegal.

Hell, running a EEC-IV here on the daily beater, but good advice indeed!
I got mine a few years ago. The stratus threw a code, and I got it cleared at Autozone. I then realized that I would probably have to do this many more times as I tried to find the vacuum leak that was not the gas cap. Best $50 I ever spent. It also makes me one of the more popular dudes at work. Get your codes dumped and cleared at lunch!
Stephana +. Yep, I am the go-to OBD guy around the ‘hood. Lots of good info on the net about the codes you find, too.
Hmmm. My local Autozones still do this.
That said, I’ve been meaning to pick one of these up for ages.
I have the next best thing, which is being grandfathered (godmothered?) into an existing relationship with a trusted mechanic. Ah, networking.