The vent control valve controls the flow of evap gases. The system will set this code of out believes the valve is stuck open allowing gases to flow all the time. If the valve checks good then I would look for a leak in the line leading up to the valve. If it is leaking, it would be the same as the valve being stuck open. The evap system monitors pressure in the system to detect leaks. If the valve was open when it shouldn't be or if the line is leaking then the evap system won't build or hold pressure and this code will set. Evap leaks can be tricky to find and often time requires an expensiveexpensive smoke machine to find the leak. Your p0420 code for the cat would not be related. That code is pretty cut and dry and indicates your catalytic converter is no longer doing its job and is unable to scrub the exhaust gasses to clean them up. This code never lies and is not influenced by anything else. If you see this code it means you need a new catalytic converter.
Yes I have checked EVAP system by smoke equipment and no leak is found. Normally how long it takes this code to appear. and also P0420 it takes a while, should it be so?
You know what I mean, for P0420 if cat converter is not doing the job, when I erase Trouble codes why it takes long to appear and always after the code P1446. point is I have run whole country including nissan centre but no definit answer only waste money.
And about P1446 vent control valve, can boost sensor on the EVAP canister be the mulfunctioning reason?