here's general info, not your code, i know, but gives some general idea
P0440 EVAP System
P0440 is defined as EVAP system incorrect purge flow. A problem anywhere in the EVAP system can cause an "incorrect purge flow". This simply means that the computer has detected that the fuel vapors are not flowing the way they should.
The EVAP system uses the engine's vacuum to periodically draw fuel vapors out of the tank through a hose and stores these vapors in a charcoal filled canister. These vapors are eventually sent through another hose to be burned inside the engine. The engine computer controls this system by monitoring the pressure inside the fuel tank, and opening an electronic valve to allow the vapor to flow or "purge".
A good service manual for your vehicle should give you a complete description of your particular EVAP system, as well as some ideas on how to test it. The problem could be as simple as a loose or damaged hose connection, or even a loose gas cap. Thorough visual inspections of the system reveal any obvious problems
now, let's get several pages for ya:
let me know how it worked out for you, i sometimes have wooshing sound when opening tank cap. otherwise - no problems what so ever. if you want my cheap recommendation - either prime your system with seafoam, maybe 4 refills, 2 cans, or drive for several tankfuls with 2 oz acetone per tankful. don't worry, i am driving with it since last fall.