I've had my Rio for 8 months, purchased brand new, and the check engine light has went off 7 times. I've had the same gas cap shpeil.
The 6th time, I was really upset when went into the dealership to get it fixed. They where nice people, but I think they uplugged the check engine light to satisfy me. So when my free oil/filter change came around, braught it in, a few weeks later, hit the highway, check engine light's on again. Braught it back again, it's been a few months no check engine light. Im thinking they unplugged it again.
Clearly it's a car with really cheap parts that just consistently break, i have forever learned my lesson.