P0440 means the ECU has detected a general malfunction in the evaporative emission (EVAP) system. This system prevents fuel vapors from escaping into the atmosphere by storing them in a charcoal canister and routing them back into the engine to be burned. When P0440 sets, the ECU knows there’s a leak, blockage, or electrical issue somewhere in the EVAP system, but it cannot pinpoint which component failed. In this guide, you’ll learn what P0440 means, its common causes, how to diagnose it, and the fixes that typically solve the problem.
What Does P0440 Mean?
P0440 is a general EVAP system fault code that appears when the ECU detects an abnormal pressure or vacuum condition in the sealed fuel vapor system. Unlike more specific EVAP codes (such as P0442 or P0455), P0440 simply indicates the system cannot hold pressure during a self-test. This test is performed by the ECU using the purge valve, vent valve, and fuel tank pressure sensor to monitor how well the system seals.
P0440 does not usually affect drivability, but it will increase emissions and can cause fuel odors. It commonly involves leaks, stuck valves, faulty sensors, or a loose fuel cap. Hot weather, cold weather, and overfilling the fuel tank can worsen symptoms or trigger the code.
Quick Reference
- OBD-II Family: P-Code (Powertrain)
- Scope: Generic
- System: EVAP (Evaporative Emission Control)
- Difficulty Level: Intermediate
- Estimated Repair Cost: €10–€250
- Last Updated: 2025-11-24
Real-World Example / Field Notes
On many GM, Toyota, and Nissan vehicles, P0440 shows up after winter or after filling the tank while the engine is running. One Toyota Corolla case involved a driver who repeatedly topped off the tank after the pump clicked off. Excess fuel saturated the charcoal canister, causing it to restrict airflow and fail EVAP pressure tests. Replacing the canister and purge valve fixed the issue. EVAP failures often start with simple habits — overfilling the tank is one of the most common triggers.
Symptoms of P0440
- Check Engine Light: Usually the only visible symptom.
- Fuel smell: Slight gasoline odor near the vehicle.
- Failed emissions test: EVAP leaks cause higher emissions.
- Hard start after refueling: Sometimes caused by purge valve issues.
- Reduced fuel economy: Rare but possible if purge flow is disrupted.
Common Causes of P0440
Most Common Causes
- Loose, damaged, or missing fuel cap.
- Faulty purge valve stuck open or closed.
- Faulty vent valve not sealing properly.
- Charcoal canister saturated or cracked.
- Small or medium EVAP system leak in hoses or connections.
Less Common Causes
- Faulty fuel tank pressure sensor.
- Leaking fuel filler neck or gasket.
- Cracked EVAP lines due to rust or heat exposure.
- ECU software needing updates (rare).
- Debris blocking the vent valve filter.
Diagnosis: Step-by-Step Guide
Begin by checking for simple EVAP issues that commonly trigger P0440. Use scan data, visual inspection, and pressure testing to isolate the problem.
Tools You’ll Need: OBD-II scanner with EVAP test capability, smoke machine (ideal), multimeter, basic hand tools, and safety gloves.
- Check the fuel cap. Ensure it clicks tightly and inspect the seal for cracks or dry rot.
- Inspect EVAP hoses. Look for cracked, brittle, or disconnected hoses around the charcoal canister and intake manifold.
- Listen for purge valve operation. A stuck-open purge valve can cause rough starts after refueling.
- Run an EVAP leak test using a smoke machine. Introduce smoke into the system to find leaks at hoses, canister, or tank fittings.
- Check the vent valve. Ensure it opens and closes properly when commanded by the scan tool.
- Test the purge valve. Use a hand vacuum pump or scan tool. It should hold vacuum when closed.
- Inspect the charcoal canister. Look for fuel saturation, cracks, or charcoal pellets in hoses (a sure sign of internal failure).
- Review fuel tank pressure readings. Unusual values may indicate a faulty pressure sensor.
- Perform a visual inspection of the filler neck. Corrosion or damage can cause slow leaks.
- Recheck the system after repairs. Clear the code, then allow the ECU to run EVAP monitors.
Pro Tip: Most EVAP leaks are found near the charcoal canister or vent valve. If you don’t have a smoke machine, many shops offer a low-cost EVAP smoke test — it’s the fastest way to pinpoint leaks.
Possible Fixes & Repair Costs
- Replace or tighten gas cap: Cheapest and most common fix (€10–€30).
- Replace purge valve: Solves issues with incorrect flow or sealing (€40–€120).
- Replace vent valve: Fixes system sealing problems (€50–€150).
- Replace charcoal canister: Necessary if saturated or cracked (€120–€250).
- Repair cracked hoses or fittings: Usually inexpensive (€10–€60).
- Replace fuel tank pressure sensor: Only if diagnosed defective (€80–€180).
Always diagnose the EVAP system thoroughly — replacing random parts gets expensive and often doesn’t fix the problem.
Can I Still Drive With P0440?
Yes, you can drive with P0440 without immediate risk of engine damage. However, the vehicle will not pass an emissions test, and you may notice fuel smells. If refueling becomes difficult or starting becomes problematic after filling up, get the EVAP system diagnosed as soon as possible.
Related Codes
- P0474 – Exhaust Pressure Sensor Intermittent
- P0473 – Exhaust Pressure Sensor High
- P0472 – Exhaust Pressure Sensor Low
- P0471 – Exhaust Pressure Sensor Range/Performance
- P0470 – Exhaust Pressure Sensor
- P0469 – EVAP Purge Flow Sensor Circuit Intermittent
- P0468 – EVAP Purge Flow Sensor Circuit High
- P0467 – EVAP Purge Flow Sensor Circuit Low
- P0466 – EVAP Purge Flow Sensor Circuit Range/Performance
- P0465 – EVAP Purge Flow Sensor Circuit
Key Takeaways
- P0440 indicates a general malfunction in the EVAP system — leak, blockage, or valve failure.
- Loose gas caps and faulty purge/vent valves are the most common causes.
- Driving is usually safe, but emissions increase and fuel odors may occur.
- Smoke testing is the quickest way to pinpoint EVAP leaks accurately.
FAQ
What causes P0440 to appear?
Most cases come from loose gas caps, cracked EVAP hoses, stuck purge valves, or saturated charcoal canisters. Leaks are the most common cause.
Can a loose gas cap cause P0440?
Absolutely. A loose or damaged gas cap is one of the most common triggers for general EVAP faults. Always check this first.
Is P0440 serious?
Not in terms of drivability, but it does increase emissions and can cause fuel odors. It must be repaired before an emissions inspection.
How do you fix P0440?
Inspect the gas cap, hoses, purge valve, and vent valve. A smoke test is the best diagnostic method. Replace faulty components based on the test results.
Can I keep driving with a P0440 code?
Yes, you can. But if you smell fuel, experience hard starts after refueling, or fail emissions testing, repair the EVAP system promptly.