P0440 Code: Evaporative Emission Control System Malfunction
🟢 Low severity · drivable
Safe to drive — this is an emissions-system fault, not an engine problem. Fix it before your next emissions test.
What P0440 means
The computer has detected a general problem in the evaporative emission (EVAP) system, which captures fuel vapors from the tank. P0440 is the general-purpose EVAP fault code, less specific than the leak-size codes P0442/P0455/P0456.
Symptoms
- Check engine light is on
- Possible faint fuel smell
- Usually no driving symptoms
Common causes
- most common: Loose, missing, or damaged gas cap
- common: Faulty EVAP purge or vent valve
- common: Cracked or disconnected EVAP hose
- less common: Faulty charcoal canister
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Tighten or replace the gas cap | Yes | $10–30 |
| Have a smoke test performed to locate the fault | Mechanic | $50–150 |
| Replace a faulty purge or vent valve | Yes | $30–120 |
Frequently asked questions
Can I drive with a P0440 code?
Yes. It's an emissions fault and won't affect drivability. Fix it before your next emissions inspection.
Is P0440 usually the gas cap?
Very often, yes. Check the gas cap first — it's the cheapest and most common cause.
What's the difference between P0440 and P0442?
P0440 is a general EVAP malfunction, while P0442/P0455/P0456 specifically point to small, large, or very small leaks.
Related codes
P0442
P0442 Code: Evaporative Emission Control System Leak Detected (Small Leak)
P0455P0455 Code: Evaporative Emission Control System Leak Detected (Large Leak)
P0456P0456 Code: Evaporative Emission System Leak Detected (Very Small Leak)
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.