I drive an 02 WRX stock, the CEL came on while I was driving, nothing noticeable in the performance of the car or anything, I parked it for the night and planned to get it read today after work. Then right as I was going to Autozone, I stopped to fill up the tank, when I get back in and start the car, the light is gone.

So anybody have any ideas? I'm pretty sure it wasn't the cap because it shouldn't have taken that long to turn on. And is the code still stored and readable or if the light goes off is it gone?