P0440
Evaporative Emission System
Low· Fix when convenientDIY friendlyPowertrainGeneric, all makes
What it means
The evaporative emission (EVAP) system traps fuel vapour from the tank in a charcoal canister and later burns it in the engine. The ECU periodically seals the system and checks that it holds pressure or vacuum. The ECU has detected a general problem in the EVAP system, often a leak or a faulty valve.
Is it safe to drive?
Safe to drive. The EVAP system only handles fuel vapour, so it does not affect how the car runs, but the car will fail an emissions test and you may smell fuel.
Symptoms
- Check engine light on
- Fuel smell in some cases
Probable causes
Most likely first
- 1Loose or faulty fuel cap
- 2Cracked EVAP hose
- 3Faulty purge or vent valve
- 4Cracked charcoal canister
How to diagnose it
Work through these in order before buying parts
- 1Record the code and its freeze frame data (speed, load, temperature when it set), then clear it and see if it comes back.
- 2Check the fuel cap and its seal.
- 3Smoke-test the EVAP system.
- 4Test the purge and vent valves.
- 5Check for technical service bulletins (TSBs) or software updates for your make and model; some codes have known factory fixes.
Common fixes
- Replace the fuel cap
- Repair EVAP hoses
- Replace a faulty valve or canister
This information is general guidance for all makes. Exact causes, specifications and procedures vary by vehicle, so confirm with your service manual or a qualified mechanic before replacing parts.