Check engine light on, car is running fine

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I have an 07 Yaris S sedan... i've never had any issue with it at all, just passed 170k miles. yesterday my check engine light came on when i was driving in town, but can't figure out why. just had a smog three weeks ago and everything checked out there. The car is not driving any different than normal, not making any sounds, and i'm not due for an oil change. we did just get back from a 5 day trip away from home, and the car was sitting in the driveway the whole time we were gone. i read on some other forums that sometimes it can be condensation in the gas tank from sitting in the sun or getting bad gas but not sure if this would be it? The last fill up was at a Valero station, and I've used less than half the tank of gas before it sat while we were gone. i am 2 hours from a dealership or mechanic, so im a little nervous to try to drive it that far if something is seriously wrong... i know this is a little vague but i'm hoping someone might have some insight here since i am really not knowledgeable in this. Thanks for anything!