You may have an intermittent problem with the vent valve on the carbon canister. It's also hard to find leaks in the fuel filler tube using a smoke machine. Do a visual inspection looking for rust flaked areas and/or holes. I always use a 3M pad to remove rust from the fuel filler where the gas cap seals and put a bit of silicon lube on the gas cap rubber seal. Easy to do.

The gas cap having a bad seal and also the fuel filler neck being rotted through are very common. Drive on salted / sanded roads? Go inspect the filler necks full lenth as a guess.

Agree could have left gas cap off have code cleared and see if it comes back on.

99% of the time it's a loose or bad gas cap.

My 2005 Nissan pathfinders check engine light came on and it had the following code in the computer P0455 Large leak detected in the EVAP system however when i took it to my mechanic (who is a little inexperienced) he hooked it up to a smoke machine and did not find any leaks. what else can cause that code to show up and how expensive of a fix is it and how can i do it