Check gas cap light came on, then check engine light came on and stayed on. Code showed gas cap was bad, replaced and problem was still there. Examined entire sytem for pressure leak and found that the fuel pressure sending unit and gasket was bad. Replaced. problem solved.
This occurred occasionally at first and then more frequently. About 40,000 miles it never went off. I had the system tested and was told there is a seal leaking at the TOP of my gas tank. Due to the cost of labor, this will be a repair close to $600.