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P0440: Evaporative Emission System Malfunction

What this check-engine code means in plain English, what usually causes it, and what a fix typically costs.

Severity: Monitor — not urgent, but should be addressed soon

What P0440 means

The evaporative emission control system (EVAP) prevents fuel vapors from escaping into the atmosphere. P0440 means the onboard computer has detected a general malfunction in this system, typically a leak or improper purge flow, but hasn't pinpointed the exact location yet.

What causes P0440?

Likely
Loose or damaged gas capThe most common cause; a missing, loose, or cracked gas cap allows fuel vapors to escape.
Likely
Cracked or disconnected EVAP hosesRubber hoses in the EVAP system can crack, split, or come loose over time, creating vapor leaks.
Possible
Faulty purge or vent valveThe purge valve or vent valve may stick open, closed, or fail electrically, disrupting vapor flow.
Less common
Leaking charcoal canisterThe charcoal canister that stores fuel vapors can crack or become saturated, causing system failure.

Is P0440 safe to drive?

Drive it?
Yes, safe to drive short-term
Watch for
Fuel smell or failed emissions test
DIY-friendly?
Start by checking and tightening the gas cap; further diagnosis may require a smoke test.

This code does not affect drivability or safety, so you can continue driving normally. However, it should be diagnosed and repaired within a few weeks to prevent fuel vapor emissions and ensure you pass emissions testing.

P0440 repair cost

~$50 – $600+

Industry-average estimates. Cost depends on the cause; a gas cap is inexpensive, while replacing valves, hoses, or the charcoal canister increases the price significantly.

Which one is it for your car?

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