My 2004 Tahoe threw a P0442 code

[ueww40]

My 2004 Tahoe threw a P0442 code the other day. 5.3 ltr flex engine. I understand it is a small leak somewhere in the evap system. I visually inspected all the lines to see if I could find something broken, but they all seem to be in order. I don't think it is the gas cap. The cap and seals look good and it feels right when I turn it the way it always has and should. How do you check the vapor canister vent valve and the vapor canister purge valve for proper operation? Should they be open or closed in home position? I inspected the vent valve to see if it was plugged up with dust or dirt, but it was not. Any ideas from experience what it could be? All suggestions are welcomed and appreciated.

 

[ueww40]

This problem has not been resolved yet. I was just away for a while. Here is what I did so far. I had my son, who vapes, blow a lot of smoke thru the AVAP service port right next to the Vapor Canister PURGE valve (the one with the green cap on and the left threaded Schraeder valve in it (for crying out loud why is the thing left threaded. I almost busted the whole thing trying to get it out until I figured out that it was a lefty.)), but that did not show any leaks. I figured, he may not be blowing hard enough so I actually went and ordered a smoke making machine, which worked like a charm, but there were NO leaks to be found anywhere. The only place where smoke came out was at the end of the line at the Vapor Canister VENT valve. I understand that the PURGE valve is normally closed (engine not running) and the VENT valve is normally open (engine not running). Can anybody explain to me what the function is of these 2 valves and how they are supposed to be doing whatever it is they are supposed to be doing while driving. Is there anything else that could cause a P0442 code?