diagnostic code P0463 cause an d cost to repair? on 2006 Buick Rainier

low fuel light has come on and after refueling light has continued to stay on even after adjusting the gas cap. Now after 4-5 days, the check engine light has come on and remains on at all times. Is this a bad gas cap or a computer problem?

Asked by for the 2006 Buick Rainier