P0440
EVAP System
Evaporative emissions (EVAP)
Generic OBD-II
Low
What it means
P0440 is a general evaporative emission (EVAP) system fault — the system that captures fuel vapors from the tank and routes them to the engine to burn instead of venting them to the air. It typically points to a leak or a faulty component, most often a loose or worn gas cap. The car drives normally; the concern is emissions and vapor loss.
Low
Can I keep driving? Yes — the car drives normally; this is a fuel-vapor containment and emissions issue only.
Common symptoms
What you'll notice
- Check-engine light on
- Occasional smell of fuel vapor near the vehicle
- Failed emissions test
- Slightly reduced fuel economy
Common causes
Most likely first
- Loose, worn, or faulty gas cap (most common)Likely
- Leaking or cracked EVAP hoseCommon
- Faulty or cracked charcoal canisterCommon
- Malfunctioning purge valveLess often
- Faulty fuel tank pressure sensorLess often
How to diagnose & fix
Work through it in order
- Check and reseat the gas cap; replace it if the seal is worn or cracked.
- Drive several complete cycles and see whether the code clears.
- Inspect the EVAP hoses and charcoal canister for cracks or leaks.
- Have the EVAP system smoke-tested to pinpoint the leak.
- Test the purge and vent valves, and the tank pressure sensor, replacing as found. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0440?+
Yes. It affects fuel-vapor containment and emissions, not how the car runs — but you'll fail an emissions test until it's fixed.
Can I just clear P0440?+
Tighten or replace the cap first, then clear it. If a hose, canister, or valve is leaking, the code returns until that's repaired.
Related codes
Often seen with P0440
Read & clear P0440 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX