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.
Can I drive?
The vehicle usually remains drivable, but fuel vapor faults should be repaired before inspection and checked promptly if there is odor.
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
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. Source notes: Code meaning verified against OBD-II reference sources; explanation is original.