P0440 indicates a general malfunction in the Evaporative Emission Control (EVAP) system, which prevents gasoline vapors from escaping into the atmosphere. This code triggers when the powertrain control module detects a gross leak or a systemic failure during the system's routine pressure or vacuum self-test. It means the fuel vapor system cannot hold the expected pressure.
A loose, cross-threaded, or missing gas cap is the most common cause, as it breaks the seal needed to hold system pressure.
Rubber hoses and hard plastic lines in the EVAP system frequently crack from age or come loose, causing a gross leak.
The purge valve or vent valve can stick open or closed due to carbon buildup or electrical failure, preventing the system from regulating pressure.
The charcoal canister can crack or become internally restricted, often from overfilling the fuel tank or water intrusion.
A defective engine computer is an extremely rare cause and is almost never the actual failure for this code.
Yes, a P0440 code generally does not affect engine performance or drivability, but it will cause a failed emissions test and may result in a noticeable fuel smell.
If a loose cap was the cause, tightening it will allow the code to clear eventually, but the monitor must run through a complete drive cycle before the Check Engine Light turns off.
It can range from free if the gas cap was loose, to moderate if a valve or hose needs replacement, to more expensive if the charcoal canister is damaged.
Almost never. Some mechanics mistakenly replace the engine computer when they cannot find the physical leak, but the failure is virtually always a mechanical issue like a cracked hose, a bad valve, or a defective gas cap.