I have the 440 code showing up on my 97. already replaced : charcoal canister,vent control valve,gas cap and still getting code. I know it could be several things so start shooting.

 

Here are things the service manual says to check.

Incorrect fuel tank vacuum relief valve
Incorrect fuel filler cap used
Fuel filler cap remains open or fails to close.
Foreign matter caught in fuel filler cap.
Leak is in line between intake manifold and EVAP canister purge volume control valve.
Foreign matter caught in EVAP canister vent control valve.
EVAP canister or fuel tank leaks
EVAP purge line (pipe and rubber tube) leaks
EVAP purge line rubber tube bent.
Blocked or bent rubber tube to EVAP control system pressure sensor
Loose or disconnected rubber tube
EVAP canister vent control valve and the circuit
EVAP canister purge volume control valve and the circuit
EVAP canister purge control solenoid valve
EVAP canister purge control valve
Absolute pressure sensor
Tank fuel temperature sensor
MAP/BARO switch solenoid valve and the circuit
Blocked or bent rubber tube to MAP/BARO switch solenoid valve
O-ring of EVAP canister vent control valve is missing or damaged.
Water separator
EVAP canister is saturated with water.
EVAP control system pressure sensor

see page 226 http://boredmder.com/FSMs/Nissan/Maxima/1997/EC.pdf

 

I ended up replacing all of the little valves/hoses on the bracket just in front of the cannister to get rid of my code. One of the nipples was cracked, but you couldn't see it because the short hose held it almost in place. I got the whole assembly from a local PullaPart lot and just swaped out the whole thing. Code has now been gone for a couple of years. Good luck.

 

Smoke test revealed a steady stream from the little 3 inch pcv valve hose coming off the valve cover.Hopefully that was it.