P0440
Moderate Severity (Level 3)Evaporative Emission Control System Malfunction
OBD-II diagnostic trouble code P0440indicates a fault detected by the vehicle's onboard computer. This code applies to all OBD-II compliant vehicles and should be addressed promptly to avoid potential engine or emissions system damage.
Severity Level 3 — Moderate
This code indicates a moderate issue that may affect vehicle performance and fuel economy. Continued driving is possible in most cases, but prompt diagnosis and repair are recommended to prevent further damage.
Common Symptoms
- Check Engine Light on
- Fuel odor from rear of vehicle
- Hissing sound from fuel tank area after engine shutdown
- No significant driveability issues on most vehicles
- May fail emissions test
Possible Causes
- Loose or faulty gas cap — always check first, most common and cheapest fix
- Faulty EVAP purge control valve — stuck open causing continuous vacuum draw
- Faulty EVAP vent control valve — stuck closed, unable to complete system test
- Cracked or disconnected EVAP vacuum hose or vapor line
- Faulty charcoal canister — saturated with fuel from overfilling tank repeatedly
- Damaged fuel tank pressure sensor
Common Fixes
- Tighten or replace gas cap ($10-30)
- Replace EVAP purge valve ($50-200)
- Replace EVAP vent valve ($60-250)
- Smoke test to locate and repair EVAP hose/vapor leak ($100-200 diagnostic + parts)
- Replace charcoal canister ($200-600)
Estimated Repair Cost
$10 – $700(typical range; varies by vehicle make and model)
These are estimated costs based on generic repair data. Actual costs may vary depending on your vehicle, location, and labor rates.
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