P0440 is same as P0441, which is detection of a lack of negative pressure in the system/(tank) and tells you to check the same things pretty much as DTC P0446. The purge/vent sensor is used to detect abnormalities in the EVAP system(charcoal canister). Signal from that sensor tells ECU that the purge VSV pressure within the CC needs regulated. If ECU senses no change, a DTC is set. I would check by the brake booster and make sure you have no leaks there, as well as up by where the stock airbox sits. The CC VSV is there, but make sure the line(tubing) running into it from the rear is hooked up to it. When both of these codes are thrown, diagnostic states this is a large leak. Sometimes these codes are thrown if the tank is overfilled a few times and the over fill check valve would become cracked or damaged. I'm betting you have a VSV stuck or a line is open/not in vacuum.
P0440 Evaporative Emisson Control Sys Malfunction: The ECM has detected abnormalities
in the evaporative emission control sys for the vapor pressure sensor and VSV for vapor sensor caused by loose gas cap
Cracked, holed, damage or loose hose or tube.
Fuel tank cap not installed properly.
Fuel tank cap cracked or damage.
Fuel tank cracked, holed or damage.
Vacuum hose cracked, holed, damage, blocked or disconnected.
Charcoal canister cracked, holed or damage.
Open or short in the vapor pressure sensor circuit.
Vapor pressure sensor faulty.
Fuel tank over fill check valve damage. ECM.
'02 IS300 MSM LSD