If it's a toyota, just put some electrical tape over the light... fixed.
My 07 honda accord did the same thing once too when I didn't close it tight enough... but on the odometer, it would spell out "CHECK GAS CAP"
I don't have a "new" new car, but with all the electronics in them, do they self diagnose and display on the screen so you don't have to take it in to see what the light is all about?