OBD-II Code · Emissions
P0440
Evaporative Emission Control System Malfunction
Severity
low
Lowest on our scale. Fix it when convenient.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$0
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
(tighten gas cap) to $300 (replace purge valve)
A fault in the evaporative emissions system. Usually a fuel cap issue or a leak in the EVAP lines.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
- Fuel smell near gas cap
- Minor fuel economy reduction
Likely causes
- Loose or damaged gas cap (check first!)Most common
- Cracked EVAP hose
- Failed purge valve
- Bad pressure sensor
Read the full diagnostic procedureP0440 is the generic catch-all EVAP code — the ECU has decided something in the evaporative emissions system isn't sealing, purging, or venting the w…
P0440 is the generic catch-all EVAP code — the ECU has decided something in the evaporative emissions system isn't sealing, purging, or venting the way it should, but it hasn't narrowed down where. The EVAP system is a closed loop that captures fuel vapors from the tank, stores them in a charcoal canister, and feeds them into the intake under controlled conditions; any leak, blockage, or stuck valve in that loop will throw P0440 or one of its more specific cousins (P0441-P0455).
The canonical first move on a shop floor is the cheapest one
- check the fuel cap.
- A worn O-ring, a cracked cap, or an owner who didn't click it three times is the cause of P0440 in roughly 30-40% of cases, and the part is $5-30.
- If the cap is good, the next step is a smoke test — pump low-pressure smoke into the EVAP service port and watch for it to escape; this is the diagnostic that catches 80% of remaining causes in one sweep, and it's why every shop doing EVAP work owns a smoke machine.
- Common leak sources behind the cap: degraded charcoal canister (the plastic cracks with age and heat), a purge solenoid stuck partway open, or debris in the vent solenoid holding it from sealing.
Vehicle-specific patternsVehicle-specific patterns worth knowing: 2005-2015 Toyota and Lexus models throw P0440 most often from a tired fuel cap O-ring or a sticky canister v…
- 2005-2015Toyota and Lexus models throw P0440 most often from a tired fuel cap O-ring or a sticky canister vent solenoid, with the vent solenoid being a known wear item that Toyota sells as a discrete part for about $80-150.
- 2003-2010Ford 4.6L applications (Crown Vic, F-150, Expedition) commonly fail at the purge valve — the diaphragm cracks and leaks vacuum into the intake, which the ECU sees as an incorrect purge flow that eventually trips P0440.
- 2007-2014GM full-size trucks (Silverado, Sierra, Tahoe) have a notorious canister vent solenoid problem because the vent line ends near the rear wheel well and gets packed with road dust and mud; a $40 vent solenoid and a clean vent line clears years of intermittent P0440 returns.
- 2008-2015VW and Audi vehicles use a Leak Detection Pump (LDP) that fails internally and triggers P0440 even when nothing else is leaking. Repair range: $5 fuel cap to $400 for purge/vent solenoid replacement to $600+ if the canister itself is cracked.
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P0440 — frequently asked
What does a P0440 code mean?
A fault in the evaporative emissions system. Usually a fuel cap issue or a leak in the EVAP lines.
What causes a P0440 code?
Common causes: Loose or damaged gas cap (check first!); Cracked EVAP hose; Failed purge valve; Bad pressure sensor.
What are the symptoms of a P0440 code?
Typical symptoms: Check engine light; Fuel smell near gas cap; Minor fuel economy reduction.
Is it safe to drive with a P0440 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $0 (tighten gas cap) to $300 (replace purge valve).
How do I diagnose a P0440 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
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