I'm not sure about the G6 but for most cars you can disconnect the battery for a few minutes then after reconnecting and starting it should clear the gas cap light.I have a 2006 G6 GT Coup with 76,000 miles on it. Recently the "CHECK GAS CAP" comes on. I have check the gas cap, I even replaced the gas cap and this morning it came back on.
I've noticed that after the "CHECK GAS CAP" message appears several time the check engine light also lights up.
Could this be something other than the gas cap?
Could this be a sensor or gas pump problem?
Oh by the was the car is running perfectly.