Something is not right with your emissions control system. This typically won't affect the performance of the engine, but can increase emissions. Here is a list of things to check. Unfortunately, tracking down the exact source can be a bit challenging.
Common Problems That Trigger the P0440 Code- Missing fuel cap
- Defective or damaged fuel cap
- Distorted or damaged Fuel Tank Filler Neck
- Torn or punctured Evaporative system hose(s)
- Defective Fuel Tank Sending Unit gasket or seal
- Split or damaged Carbon Canister
- Defective Evaporative Vent Valve and/or Evaporative Purge Valve
- Defective or damaged fuel tank