P0440: Evaporative Emission System Malfunction
Updated November 7, 2026
The EVAP system traps fuel vapor from the tank and later burns it in the engine. P0440 is a general fault: the engine computer found a problem with the system, usually a leak or a valve that isn't working, but it doesn't say exactly where.
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🔧 Want to check this yourself? An OBD2 scanner reads the code; models with live data also show the sensor readings used in the checks below. See code readers and scanners from $24.99 ↓ · Which scanner do I need?
Common causes
- A loose, damaged or wrong gas cap
- A cracked or disconnected EVAP hose
- A faulty purge valve or vent valve (solenoid)
- A cracked charcoal canister or a failed leak-detection pump on vehicles that have one
Code meanings can vary slightly by manufacturer. Use these as a starting point and confirm with your vehicle's service information or a mechanic before replacing parts.
Symptoms
- Check engine light, usually with no drivability symptoms
- Sometimes a faint fuel smell
- A failed emissions or inspection test
Is it safe to drive?
Generally safe to drive with a steady check engine light. If you smell strong raw fuel, don't drive it until the leak is found.
How to check it with a scanner
- Plug an OBD2 scanner into the port under the dashboard and read all stored codes and the freeze-frame data (the conditions when the code set).
- Check that the gas cap is tight and its seal isn't cracked; clear the code and see if it returns.
- Scan for more specific EVAP codes (such as P0442, P0455 or P0456).
- Inspect EVAP hoses near the engine and tank for cracks or loose connections.
- With the engine off, test the purge valve with a hand vacuum pump; most should hold vacuum when unpowered. A smoke test at a shop is the surest way to find a leak.
- After a repair, clear the code and drive normally for a few days to confirm it doesn't come back.
A basic code reader shows the code; scanners with live data let you watch sensor readings, which is what you need for most of the checks above. See OBD2 scanners under $100.
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Questions
What does P0440 mean?
P0440 is the generic OBD2 code for "Evaporative Emission System Malfunction." The EVAP system traps fuel vapor from the tank and later burns it in the engine. P0440 is a general fault: the engine computer found a problem with the system, usually a leak or a valve that isn't working, but it doesn't say exactly where.
Is it safe to drive with P0440?
Generally safe to drive with a steady check engine light. If you smell strong raw fuel, don't drive it until the leak is found.
How do I check P0440 myself?
Read the code and freeze-frame data with an OBD2 scanner, then: Check that the gas cap is tight and its seal isn't cracked; clear the code and see if it returns. Scan for more specific EVAP codes (such as P0442, P0455 or P0456). Inspect EVAP hoses near the engine and tank for cracks or loose connections. With the engine off, test the purge valve with a hand vacuum pump; most should hold vacuum when unpowered. A smoke test at a shop is the surest way to find a leak.
Related codes
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