EVAP System Malfunction
The P0440 code indicates a general malfunction in the Evaporative Emission Control (EVAP) system, which is designed to prevent fuel vapors from escaping into the atmosphere. The Engine Control Module (ECM) sets this code when it detects a leak or a failure to hold pressure during the EVAP system's automated self-test.
This code does not typically affect drivability or safety, meaning the vehicle is safe to drive in the short term. However, it will cause the vehicle to fail an emissions test and should be repaired to prevent environmental pollution.
Common symptoms
- Illuminated Check Engine Light
- Noticeable fuel odor around the vehicle
- Slight decrease in fuel economy
- Failure to pass a state emissions inspection
- No noticeable drivability issues (engine runs normally)
Likely causes
- Loose, damaged, or missing gas cap
- Leaking, cracked, or disconnected EVAP vapor hoses
- Faulty EVAP purge valve or solenoid
- Faulty EVAP vent valve
- Damaged or cracked charcoal canister
- Faulty fuel tank pressure sensor
What to check before replacing parts
Inspect and tighten the gas cap.
Look for: Check if the gas cap is loose, missing, or has a cracked or worn O-ring seal. A damaged seal indicates the cap needs replacement.
Perform a visual inspection of the EVAP hoses and lines.
Look for: Look for cracked, disconnected, or degraded rubber hoses in the engine bay and near the fuel tank or charcoal canister.
Test the EVAP purge valve.
Look for: Apply vacuum to the purge valve when it is unplugged; it should hold a vacuum. If it allows air to pass through when de-energized, it is stuck open and faulty.
Test the EVAP vent valve.
Look for: Command the vent valve closed using a bi-directional scan tool and attempt to blow air through it. If air passes through while commanded closed, the valve is defective.
Perform a smoke test on the EVAP system.
Look for: Introduce automotive smoke into the EVAP test port. Look for smoke escaping from hoses, the canister, the gas cap area, or the fuel tank filler neck, which pinpoints the exact location of the leak.
This page explains the generic P0440 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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