Error code P0455 large EVAP leak

I am a home mechanic, and don't have access to all these speciality tools. Did you read my explanation of the problem? The system seems to be able to hold pressure for at least several minutes, so what would a smoke test show? If the system is not blocked and there is no leak what else can trigger the error code?

Code po455 came up on diagnostic. It came up with large leak detected in EVAP system. I checked fuel cap and it was tight. It said EVAP canister might be broke, hose cracked or not connected. Cant locate EVAP canister. It also said purge or vent solenoid might be defective. Where is this? Any help would be greatly appreciated!

So I have a 2006 SS 52K miles and have the same code. Tightened the cap to no avail. Replaced the fuel cap, hoped for cel to go off. Nothin. Now noticing sudden drop in mpg. Took it in to dealer to check and they got same code (p0455) and tested pressure, said all was fine, take it home. I cannot spend this kind of money of gas! What to do next? Let me know what you find out, I find it ironic that we are driving almost the same car and have the same problem at the same time! Hmmmmmmm. I've been surfing everywhere for answers, nothing yet. I'm wondering if a smoke test is necessary since the pressure is fine, maybe a very small leak needs to be found. I don't know a thing about cars though, so who knows. Good Luck!

I've got the same problem. It started out with the 'tighten gas cap' message and then eventually idiot check engine light with same code, 'large evap leak'. I changed gas cap, which was not tightening. It would just pull out straight after trying to tighten. So I spoke to dealership tech that told me that it may be vent solenoid located behind gas cap (you can see solenoid by getting under car and looking under rear quarter from underneath. I also followed the large line from solenoid that routed toward tank and I noticed a plastic barbed coupler joining to the extended line. These lines could spin freely on the barbed fitting but not be removed too easily. I haven't got into it much more than that, but I may pull it apart and see if hose is worn. But it has to be a large leak and the cars are too new (i believe) to be having identicle problems of something being broken. Maybe bad solenoid or maybe that fitting. Not sure. But I'll look more into it when I get time and maybe a little more research. Let us know if anyone hears anything different. Thanks for listening

I have the same problem 2006 SS

Have the same problem with a 2006 impala LT. Took it in the shop three times. Changed gas cap, smoke tested the car three times, could not find a leak. Now car is out of warranty and have had the problem ever since I purchased the car. Very frustrated. Now I can't even get an inspection because of the check engine light and three different mechanics could not find the problem to repair it. I will never buy a chevy again. Worst piece of **** I have ever owned.