COULD IT BE RUBBER VENT HOSE
INFORMATION LIGHT READS GAS CAP PUT NEW GAS CAP LIGHT DOES NOT GO OFF on 1999 Cadillac DeVille
It may have a small leak in the evaporative emission system. It could be about a dozen different things. Have a professional diagnosis done.
problem was solved it was the gas filler neck that was leaking fumes detected by puting smoke in the system