The check engine light has been coming on in my car for two weeks now. Having just got the car serviced two months ago, I took it to Auto Zone to have a diagnostic test run on it. The man told me the problem could either be my gas cap [which was indeed cracked in two places] or an electrical issue from my fuel gauge [or something like that]. We replaced the gas cap and was told that should fix it, but the check engine light still has not gone off. The car was driven for about 20 miles after the cap was replaced. Should the light have gone off by now if the gas cap was the problem? Or should I get said fuel gauge issue checked, even though the fuel gauge works? Please help!
First, they should have reset the light at the store. It may not go off itself. You could try disconnecting the battery for about 10 minutes to see if that resets it, but if it is a hard codes in the computer, it won't.
Go back where you got the fuel cap and have them reset the computer. Now keep in mind, the cap could be the problem or there may be a leak in the EVAP system. If the light comes back on, have the system fogged. Basically, a mechanic will force fog into the EVAP system. If there is a leak, the fog will leak out at that point. Most commonly, the leaks are not the fuel cap but rather the filler tube (the steel pipe where you put the gas). They rust, get small pin holes in them and create a leak which the emissions system picks up on and sets the computer.
Have it reset, ask them to tell you the code that is presently in the system, and let me know what you find.