Phoebe's check engine light went on in June in the midst of moving. I had just bought gas (and yes, I tightened the cap enough -- I always count six clicks), and it was my first over-$40 fillup, so I foolishly told Phoebe that she was expensive. Silly me -- I know better than to talk to her like that. Her light was on in less than two miles.
I haven't driven her nearly enough since, but today I finally managed to take her to Advance Auto Parts to have the code checked. The guy helpfully plugged the scanner in, and it directed me to start the car, which I did. The light went out. Then it wanted me to turn the car off for ten seconds and restart it. After I did that, it produced an error because it couldn't read the code. We repeated the scan and got the same error. The guy asked if the light was still on, and I told him it wasn't. Turns out it can't read the code if the light isn't on anymore. Whatever it was, the light has gone out.
I suspect Phoebe just wanted a little attention.