mine just started doing it today...and whats weird is I haven't even touched the cap in over 2 weeks

 

Had this happening on a silverodeo and a buick rainer. Replaced cap on both and light still came on. Delt with it for couple of months and then out of the blue it fixed it self. Only thing different i did was spray the tank with a pressure washer. Think there might be a vent somewhere that was cloggged.