A P0440 error code on your Nissan means there is an evaporative emission control system (EVAP) malfunction. Typically no symptoms of this problem appear, but the error code will cause problems with emissions testing and may indicate dangerous fuel leaks.
The EVAP system controls the transmission of fuel vapors in order to prevent leaks of flammable gasoline into the air. The Nissan EVAP system consists of a gas cap, the fuel lines, a carbon or charcoal canister, a purge valve and assorted hoses.
The P0440 error could be caused by several issues. The first potential issue to check is that the gas cap is on and tightened properly. Open and replace the gas cap, then reset the error code. Use your vehicle as usual for the next 24 to 48 hours, and see if the error P0440 returns.
If the error continues to display after you have checked the gas cap, likely there is a leak somewhere in the EVAP system. Inspect all hoses for leaks, or take the Nissan to a local repair shop or dealership to test the system with a smoke machine that will detect leaks. If there are no leaks, then there might be a problem with the purge solenoid on your Nissan, or the carbon canister may have a clog or some other dysfunction.
