QuestionI found this answer. "You've got a blockage that's preventing the vapors from exiting the fuel tank (or the fuel from entering the tank). Most likely, you'll need to have the car professionally diagnosed to determine the issue. Usually, when this occurs, the check engine lamp comes on and a code P0446 or P0449 is stored.
Common blockage issues are with the canister close valve and the canister filter. But you could also have a defective fuel cut valve in the tank or a blocked canister. You could also have a problem with a restricted hose or pipe either not allowing proper venting or not allowing the fuel to enter the tank properly."
OK, so how do I fix this? Finding out WHAT doesn't fix it, and there's GOT to be a way. HELP!!
AnswerI'll presume that you're having an issue with premature fuel pump automatic shut-off, since that's what this answer pertains to.
One of the problems with this issue is that there are a large number of potential problems that can cause the same symptoms. You'll need to do some diagnosis to find where the problem lies.
The place to start is with the easiest diagnosis. That would be anthing you can check visually. You'll need to make sure that the fuel filler hose is not twisted and that the filler neck hasn't been pinched partially shut. You'll need to verify there's no physical damage to the fuel tank. You'll need to verify the evaporative hoses aren't twisted and the metal lines aren't pinched.
If you find nothing wrong visually, then you'll need to apply either pressure or vacuum to the fuel tank to perform further diagnosis. Then start with the item closest to venting to atmosphere, the canister filter. Take it loose. If that caused the vacuum/pressure to release, the filter was the problem. If not, move up the line to the next component in line, the canister close valve. Remove that. If the pressure releases, the canister close valve was the problem. If not, move on to the next component, the hose between the cansiter and the close valve. You'll need to continue systematically with this method until you reach the problem. Some of the items will be on top of the fuel tank and largely inaccessible without removing the fuel tank.
Since most people don't have the equipment to perform this type of diagnosis or to remove the fuel tank, I've suggested that professional diagnosis will probably be necessary. Canister filters, canister close valves, and charcoal canisters are frequent culprits. There were also some problems with 1996-2000 Elantras with the fill vent valve in the top of the fuel tank sticking shut. I don't think I'd recommend anything beyond the cansiter filter as a guess to see if that solves the problem. After that, the probabilities go down, the parts become more expensive, and the effort required for replacement is significantly more in the case of the fill vent valve.
