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P0456 Evaporation Leak Code Question

I have a 2000 Buick Park Avenue Ultra with 141,000 miles on it. Recently my check engine light came on while driving and a little after that my car stalled. When trying to restart the car it sounded like it wanted to turn over and was just waiting for the final start. The engine finally turned over after a couple of minutes and ran perfectly fine, but the check engine light was still on. I went to Auto Zone, which was a block and a half away to get the code for the check engine light. They ran it and gave me the code P0456 which is for a small fuel evaporation leak. The gentleman informed me the most common reason for that is a faulty gas cap. I inspected the gas cap, and the o-ring on it was cracked and worn, so I replaced it. I hit the reset for the code and everything was peachy. The next day my the check engine light came on again and a little after that my car stalled, again. I took it again to Auto Zone and the same code, P0456, came up again. Any suggestions as to what might be the problem? Both times it happened I was idling at a stop light. I would like to get an idea of what is going on before I take it in, most likely tomorrow.

You are trying to present the evap leak and the engine stalling as a connected problem. They probably are not…I suppose a purge valve stuck open could do it, allowing tank vapors to pour into the engine at idle and in effect flood it…

The only way the EVAP system could be related to the operating problem is if the charcoal canister were saturated, preventing the fuel pump from pumping once the vacuum developed beyond a certain point. That would also eventually overstress and kill the fuel pump.

I would definitely have the fuel line pressure checked. And have you been smelling gas from under the hood?