P0440 is a general EVAP System trouble code indicating something with your vehicle's EVAP system is not functioning properly. We recommend performing a physical inspection of the EVAP system. You should inspect 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.
Also having trouble code P0446 triggered helps in diagnosing trouble code P0440 because P0446 is an EVAP system specific trouble code indicating a problem with the EVAP Vent Control Circuit.
Check for a faulty vent valve. The vent valve may be stuck open, dirty (causing high resistance) or shorted out. More than likely upon repairing (replacing) the EVAP vent valve you will clear both trouble codes P0440 and P0446 at the same time.
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. Code also may refer to ECM detecting that EVAP system is unable to achieve or maintain vacuum during test.
