How do you fix a problem with the Evaporative purge flow system code P0440 on a 2001 Camry?

There are choices. First one is it's a glitch, and what you need to do is just to reset the computer (it happens sometimes especially if it's humid around). Second one is a malfunctioning sensor. Most of the time the sensor located on the charcoal canister fails (~$200 with labor; price depends on state).