Things I've had done: Replaced Gas cap. Pressurized all vacuum hoses and replaced the Tank ventalation valve. All to no avail. I've checked the expansion tank and hoses leading to it. No leak noted or heard. Shop wants to remove the gas tank to check lines. They quoted 5 hours labor alone. Does not sound right for Code P0455. What else can cause a P0455 code. Without having to remove gas tank. Need help....thank in advance.