P0440: Evaporative Emission System Malfunction
The system that traps gasoline vapor from your fuel tank has a general fault.
Severity: 1 of 4
Generally safe to drive. EVAP faults do not affect how the engine runs in most cases. You will likely fail an emissions inspection until it is fixed. If you smell raw fuel strongly, find the source promptly, because a liquid fuel leak is a fire risk.
Estimate range covers the repairs listed below; see the cost breakdown. A flashing check engine light, a hot temperature gauge, or brakes that feel different mean stop driving and get help.
What P0440 means
Your fuel tank gives off vapor. Instead of venting it to the air, the evaporative emission (EVAP) system stores it in a charcoal canister and later burns it in the engine.
The computer periodically seals the system and checks whether it holds pressure or vacuum. P0440 is a general fault that the system did not behave as expected. Newer vehicles usually set a more specific code instead.
Common causes (cheapest likely first)
- Loose, damaged, or wrong gas cap. Always check this first. Tighten until it clicks.
- Cracked EVAP hose. Rubber and plastic lines age and crack.
- Faulty purge valve. Controls flow of vapor to the engine.
- Faulty vent valve. Often near the canister, and exposed to dirt and water.
- Damaged charcoal canister. Can be ruined by overfilling the tank.
Symptoms
- Steady check engine light
- Usually no drivability symptoms
- Faint fuel smell
- Failed emissions test
DIY difficulty: Easy to moderate
Gas caps are easy. Valves are often simple to swap but finding leaks usually needs a smoke tester.
Tools: OBD-II scanner, Replacement gas cap, Basic hand tools, Smoke tester (shop tool)
Estimated repair cost
This is an estimate, built from typical parts price ranges plus labor hours times an assumed shop rate of $110 to $190 per hour. Actual prices vary by vehicle, region, and shop. Diagnosis fees are often extra.
| Repair | Parts | Labor | Estimate (low / high) |
|---|---|---|---|
| Gas cap | $10 to $35 | 0.0 to 0.1 h | $10 + 0.0 × $110 = $10 $35 + 0.1 × $190 = $54 |
| Purge or vent valve | $25 to $150 | 0.3 to 1.5 h | $25 + 0.3 × $110 = $58 $150 + 1.5 × $190 = $435 |
| Charcoal canister | $80 to $400 | 0.8 to 2.0 h | $80 + 0.8 × $110 = $168 $400 + 2.0 × $190 = $780 |
Watch a repair video
How to Find an EVAP Leak (P0440, P0442, P0455, P0456). Third-party video, loads from YouTube (privacy-enhanced mode) only when you press play. Procedures vary by vehicle. Search YouTube for “P0440 fix” videos.
By make
This code works the same way on every make. See brand notes.
Repair manuals
Step-by-step service manuals with torque specs and wiring diagrams:
Haynes manuals Chilton manuals
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Related codes
Check for recalls
Before paying for a repair, enter your VIN in the NHTSA recall lookup. Emissions parts may also be covered by a federal emissions warranty; check your warranty booklet.
FAQ
Can a gas cap cause P0440?
Yes. It is the first thing to check.
Will P0440 hurt my engine?
Rarely. It mostly affects emissions.
How do I avoid EVAP problems?
Stop filling when the pump clicks off. Topping off can push liquid fuel into the canister.