OBD codes / P0440
P0440
MinorEvaporative Emission System Malfunction
P0440 is the lowest-urgency category — it does not affect performance or safety, only emissions. Try tightening (or replacing) the gas cap first; if the light clears after a few drive cycles, that was it. It will fail an emissions test until resolved, so fix it before inspection.
What this code means
The evaporative emission (EVAP) system traps gasoline vapors from the fuel tank and routes them back to be burned, instead of venting them to the air. P0440 is a general fault that the system isn't sealing or flowing vapor correctly. The classic cause is a loose, worn, or missing gas cap — the cheapest fix in all of OBD — but a cracked EVAP hose, a stuck purge or vent valve, or a leaking charcoal canister can also set it. It has no effect on how the car runs; it's purely an emissions and inspection issue.
Symptoms you might notice
- Check-engine light with no change in how the car drives
- Occasionally a faint fuel smell
- Sometimes triggered right after refueling or a loose gas cap
- Failed emissions test
What it costs to fix
Typical range: $20–$400 · about ~0.2–1.5 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Gas cap | $10–$35 | ~0–0.2 hrs |
| Purge or vent valve | $20–$120 | ~0.3–1 hrs |
| EVAP hose / line repair | $10–$80 | ~0.3–1 hrs |
| Charcoal canister | $100–$350 | ~0.5–1.5 hrs |
Start with the gas cap — it's the cheapest possibility and a surprisingly common cause. The expensive end is a charcoal canister. A smoke test (a small diagnostic charge at a shop) is usually what pinpoints a hidden leak.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0440 for my exact vehicle →
Frequently asked
Can I drive with P0440?
Yes — it has no effect on how the car runs or on safety. The only real consequence is failing an emissions test, so you can drive normally and address it at your convenience (ideally before inspection).
Will tightening my gas cap fix P0440?
Often, yes. A loose or worn gas cap is one of the most common causes. Tighten it until it clicks, or replace a cracked one, then drive a few cycles — the light may clear on its own. If it comes back, the leak is elsewhere.
How much does it cost to fix P0440?
Frequently almost nothing — a gas cap is the cheapest repair in OBD. If the cause is a purge/vent valve or a hose it's still modest; a charcoal canister is the priciest typical outcome. A smoke test is the usual way to find a hidden leak.
Why did P0440 appear right after I got gas?
Because the EVAP system is sealed and tested around the fuel tank. A gas cap left loose or not clicked tight after fueling is a textbook trigger — check it first before anything else.
Seeing P0440 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0440 for my vehicleGeneric OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.