P0440 is a general EVAP trouble code indicating a problem with your Toyota Corolla's EVAP system. An inspection of the EVAP system we be necessary. Check for the following:
- loose or defective fuel tank cap
- incorrectly routed or defective EVAP system vacuum and vapor lines
- stuck closed EVAP Vent Valve
- defective EVAP vent valve
- restricted or blocked EVAP system hose
- restricted or stuck closed fuel tank rollover valve (if equipped)
- malfunctioning or damaged vapor (EVAP) canister.
- defective VSV (vacuum switching valve)
P0446 will help in diagnosing trouble code P0440 because P0446 is a specific EVAP system trouble code, indicating a problem with the EVAP Vent Control Circuit.
Your Corolla's EVAP vent valve may be stuck open, dirty (causing high resistance), or shorted out. The vent valve is used to seal the EVAP canister. More than likely upon repairing (replacing) the EVAP vent valve you will clear both trouble codes P0440 and P0446 at the same time. The vent valve is part of the Toyota Corolla EVAP Charcoal Canister, and must be replaced as one unit.
EVAP Vent Valve Operation:
EVAP vent valve is used to seal the EVAP system (charcoal canister, gas tank, vapor hoses) in order for the ECM to pressurize the EVAP system and ensure there are no leaks. The vent valve is usually supplied Batt. voltage with key on. The ECM's driver controls the ground, and when grounded, activates the valve (closing it). If the ECM detects a short to ground, and open,or a short to battery voltage on the control circuit, P0446 will set. P0446 can also set when the ECM detects that EVAP system is unable to achieve or maintain vacuum during test.
Faulty VSV (Vacuum Switching Valve) - Another common failure which could trigger trouble code P0440 is a defective VSV. The VSV is part of your Toyota's EVAP system and is located on the charcoal canister. The VSV is used to divert fuel tank pressure from the fuel tank to the charcoal canister in order for the fuel tank pressure sensor (FTP) to determine adequate fuel vapor containment.
The VSV is activated while your Toyota's ECU is performing an EVAP monitor test. When grounded, the VSV should block fuel tank vapors/pressure from leaving the fuel tank. When not grounded, the VSV should divert fuel tank pressure to the charcoal canister. It is highly recommended that when replacing the VSV, the charcoal canister is replaced as well. The charcoal canister is an intricate device with many internal diaphragms, springs, and valves. It is not designed to last the life of a vehicle, and will require replacement during some point of a vehicle's life. If in fact your Toyota's VSV has malfunctioned, it would be safe to assume the charcoal canister is near the end of its functional life as well.
