Diagnostic code
P0440 Code: EVAP System Malfunction
P0440 is a broad EVAP system fault. Instead of identifying a specific leak size or valve circuit, the computer is saying the fuel vapor control system did not pass its expected self-test.
Educational reference only, not professional repair advice. A fault code is a starting point, not a diagnosis. Vehicle symptoms, live data, service history, and manufacturer-specific procedures change the repair path. If the check engine light is flashing, the vehicle is overheating, brakes or steering feel unsafe, fuel odor or smoke appears, or the engine is running poorly, stop driving when safe and get professional help.
Sources
Safety limits for this page
Use this page as a reference only. Do not perform hazardous repairs from a web guide. Stop when safe and contact a qualified mechanic if any warning condition below applies.
- Opening fuel lines, fuel tanks, or pressurized fuel components
- Flashing check engine light
- Overheating, smoke, or strong fuel smell
- Loss of power, severe shaking, unsafe braking, or unsafe steering
- Fuel odor, visible leak, smoke, or hard starting after refueling
Can I drive?
The vehicle is usually drivable, but EVAP faults block emissions inspection in many US states. Repair before the next inspection. Investigate promptly if you smell raw fuel.
Repair range
$30-$750
Scanner note
Basic OBD-II scanner with live data
Plain-English Meaning
P0440 is a broad EVAP system fault. Instead of identifying a specific leak size or valve circuit, the computer is saying the fuel vapor control system did not pass its expected self-test.
Common Causes
Common possibilities (most common first):
- Loose gas cap
- EVAP hose leak
- Purge valve stuck open or closed
- Vent valve fault
- Charcoal canister damage
Order varies by make, model, mileage, and operating conditions. Do not replace parts based only on this list — verify with a scan tool and qualified mechanic.
Symptoms
- Check engine light
- Fuel vapor smell
- Failed emissions test
- No clear drivability symptom
Diagnostic Steps
- 1Check for related EVAP codes
- 2Inspect cap and easy-to-see hoses
- 3Smoke-test the vapor system
- 4Test purge and vent valve operation
- 5Clear codes only after confirming the repair
Confusable And Related Codes
P0455
Compare →P0455 means the fuel vapor system cannot hold pressure or vacuum during its self-test, and the leak appears large. A loose gas cap is a common simple cause, but hoses, valves, and the charcoal canister can also leak.
P0442
Compare →P0442 means the evaporative emissions system detected a small vapor leak. The vehicle may drive normally, but the fuel vapor system is not sealing tightly enough during the onboard leak test.
P0446
Compare →P0446 means the EVAP vent control system is not behaving as expected. The vent valve may be stuck, blocked, electrically faulty, or unable to seal the fuel vapor system during testing.
P1450
Compare →P1450 usually means the vehicle cannot relieve fuel tank vacuum as expected during EVAP operation. It is often associated with purge or vent control problems, a restricted vapor path, or a fuel tank pressure reading that does not change nor
FAQ
What makes P0440 different from P0455?
P0440 is more general, while P0455 points to a large EVAP leak.
Can P0440 be a gas cap?
Yes. The gas cap is a simple first check before deeper EVAP testing.
Will P0440 make the car run badly?
Usually no, though a stuck purge valve can sometimes affect idle or starting.
This page is educational and is not a substitute for hands-on vehicle diagnosis.