I have a P0455 message on my 1998 SLK230 with about 70,000 miles. Besides the check engine light, occasionally the yellow low fuel light will blink even when the tank is half full. I have checked the gas cap, flipped the gasket and lubricated it and it seems to hold well. If I come back to the car after it has been off for several hours, and loosen the gas cap, I get a good blast of pressure from in the tank so i think it is holding well. I have cleared the code and it comes back. What would be the next area to check for this fuel system message.