P0440: Evaporative Emission System Malfunction
What to do
Driveable, and you will almost certainly notice nothing. It will fail an emissions test. Before anything else, check the fuel filler cap is properly tightened — it is the single most common cause and costs nothing to rule out.
What this code means
A general fault in the evaporative emission control system. The system exists to stop petrol vapour escaping from the fuel tank into the atmosphere: vapour is collected in a charcoal canister, stored there while the engine is off, and drawn into the intake to be burnt once conditions allow. It is entirely a containment system and contributes nothing to how the engine runs, which is why almost every fault in it is invisible to a driver.
The module tests it by sealing the system and either applying vacuum or pressure and watching whether it holds. That is worth knowing because it explains the diagnostic difficulty: the fault is a leak somewhere in a sealed circuit spanning the tank, the filler neck, the canister and several metres of pipe, and the code rarely says where. A smoke machine is the tool that turns this from guesswork into a five-minute job.
Likely causes
Start here
- Loose or missing fuel filler cap · easy
- Cracked or perished EVAP hose · moderate
- Faulty EVAP purge valve · easy
Less common
- Faulty EVAP vent valve · moderate
- Saturated charcoal canister · moderate
- Faulty fuel tank pressure sensor · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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