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Thank you for allowing me to help you with this concern today and am sorry to hear that this is happening. I will have to ask you a few questions so that I can get a better understanding as to what may be going on with your Tundra.
The P0455 code is for a Gross (very large) EVAP Leak, have you tried just clearing the code, tightening the gas cap and then seeing if the code returns? This system will check itself every night.
It sounds to me like they are guessing at this repair. Let me ask..
Did they smoke test the system to "find" this leak?
Did they offer to show you what is leaking (these hoses) on your Truck?
It doesn't sound like you were taken care of at all on this. The way this EVAP system works is to test if raw gas is leaking out into the air. This is emissions and we don't want raw gas just escaping into the atmosphere.
The vacuum pump/canister will draw a vacuum on the system and watch how long that vacuum lasts. Now lets say you left your gas cap loose, the vacuum wouldn't last very long and the system would fail this turning your check engine light on and setting the P0455 Gross Evap leak. This happens every-night your trucks sits for 5 hours or longer.
Does this make sense to you?
What I would do, is tighten the gas cap and clear the code (this can be done by using a scantool like from Autozone or disconnecting the battery for 1-2 minutes) then just driving it like you normally for 1-2 days. If there is a true problem, which I doubt there is, then the P0455 code would return back on. I doubt it will. We rarely see any problems out of these system unless the cap was not put on fully.
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Hello, my name is***** are valves built into canister. If dealership said canister is the problem then I would take their word on it and have it replaced. Here is also information from manual on code so you can see possible causes and testing that should be done. Let me know if you have more questions, thanks.