We experienced another warning light, this week. After getting a scan, it was a leak in the fueling system vacuum. I had checked to make sure the gas cap was tight, first thing. Although the cap was tight, the O-ring was degraded. My tech spotted it right away. A replacement from Towne is $23. We turned the O-ring over and it sealed. I also cleaned the top of the gas fill neck too. 

As of now, the warning light is off and I'll shop for a new cap or O-ring.