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P0440: Meaning, Symptoms, Causes, Diagnostics, and Fixes

The P0440 OBD2 code is one of the most common causes of check engine light activation on modern cars. It’s also often one of the easiest to fix. 

This is the code that will activate if you don’t put your gas cap on tightly enough after a fill-up. Very often, all you’ll need to do to clear it is make sure your gas cap is secure. This isn’t the only source of the P0440 code, however. It could also come up because of leaks in your system.

While the P0440 code isn’t serious, you’ll need to fix it before your next emissions test. Read on below to find out more about this code, what it means, and how to clear it from your system.

P0440 Code Definition

Evaporative Emission Control System Malfunction.

What Does P0440 Mean?

The P0440 OBD2 code triggers when there is a problem with the pressure in your evaporative emission control (EVAP) system. It could mean that there is a leak, or that one of the sensors in the system has malfunctioned. 

The EVAP system’s role in your system is to keep harmful gasses from escaping into the atmosphere through your emission. Fuel vapors go through the system into a chamber with a charcoal canister. These charcoal pellets absorb harmful compounds, releasing the cleaned air back into the intake manifold.

OBD2 scanners can help you detect the p0440 code.
You can detect the p0440 code by using OBD2 scanners.

If your EVAP system is leaking, this could cause your vehicle to fail state emission tests. This is the main reason you’ll want to find the source of this trouble code as soon as you see it come up.

What Are The Symptoms of The P0440 Code?

Your car likely won’t drive any differently when the P0440 code is active. The symptoms are likely to be mild, including:

  • Activation of the check engine light
  • Fuel smell around your vehicle

What Are The Causes of P0440?

  • Gas cap is damaged or loose (most common cause)
  • Hoses in EVAP system are leaking, damaged, or disconnected
  • Purge valve or purge solenoid are faulty
  • Vent valve is faulty
  • Charcoal canister is leaking
  • Fuel tank is damaged or leaking
  • Fuel vapor pressure sensor is damaged or faulty

How Serious Is The P0440 Code?

The P0440 OBD2 is not serious. There will likely be no drivability issues, and there is a low potential for damage to your vehicle. The main reason to address this code is to prevent your car from failing emission tests. 

How To Diagnose The P0440 Code

Tools you’ll need:

  1. Scan your car for other trouble codes. If any other codes come up related to the EVAP system, fix those first. 
  2. Inspect your gas cap for damage. Tighten it if it’s loose and replace it if you notice any visible signs of deterioration. 
  3. Scan your system and look at the freeze frame data. This can help you tell when the fault happened and guide you toward the potential source of the problem.
  4. Check the hoses around the EVAP system for damage, leaks, and cracks. You can do this by feeling them for imperfections and looking for visual cracks. For a more thorough inspection, you can conduct a smoke test. Connect a smoke machine to your EVAP system and turn it to “visible vapor” or “smoke” mode. Also make sure all hoses are connected securely.
  5. Inspect your charcoal canister and fuel tank for leaks. 
  6. Use a vacuum pump to test your purge valve and make sure it’s not stuck or leaking. Disconnect the line running to the purge valve. Set the vacuum pump to 17 psi and apply it to the pump. It should hold the vacuum without leaking. If the gauge on the pump drops, the valve is failing and should be replaced.
  7. Ensure the purge valve and solenoid are receiving power using a digital multimeter. If not, replace the faulty component.

Common Mistakes To Avoid While Diagnosing The P0440 Code

While the gas cap is often the cause of P0440, don’t just replace the cap and assume that will fix the problem. Still scan the system to make sure the code is cleared and run a full diagnostic if it comes up again.

What Should You Do To Fix The Code P0440?

Don’t forget to clear trouble codes and scan your car again after every repair. This will let you know if you’ve fixed the problem or if you need to continue with your repairs.

The P0440 trouble code doesn’t always clear permanently. You may find it goes away for a while after you tighten your gas cap, then reappears. This could be a sign of unfixed leaks in your fuel tank or EVAP system. If this happens, start with step 2 of the fixes after you’ve ensured the gas cap is tight.

  1. Replace your gas cap, even if you don’t see damage. This is the most likely cause of the P0440 trouble code. Since gas caps are fairly cheap, it’s a simple repair that can save you a lot of time. 
  2. Replace any damaged or leaking hoses you found around the EVAP system. Ensure the new hoses are installed securely.
  3. If the pump valve fails the vacuum or multimeter test, replace it.
  4. Use a smoke machine on your entire EVAP system to ensure the entire system is secure. Make sure you pay attention to the charcoal canister as well as the hoses. Replace any components you find to be leaking. 
  5. Replace the fuel vapor pressure sensor. 
How to fix the code P0440?

Tips To Avoid P0440 In The Future

The easiest thing you can do to keep the P0440 is to make sure you replace the gas cap firmly after every stop at the gas station. Leaving your gas cap loose can allow grit and debris to work its way into the threads, which can eventually cause damage to both the cap and the fuel neck. Making sure your gas cap is tight will prevent this potential problem.

Read more: OBD2 Codes: Full List Meaning & Fix Guide

Tim MillerFounderOBD Advisor

I’m Tim Miller from Denver, Colorado. I’m the founder of obdadvisor.com, an automotive blog about "Diagnostic Tools and Auto Repair". My fan page is facebook.com/autozikcom. I've been working as an automotive mechanic and blogger for over 10 years writing articles to share my experiences and expertise.

Web: https://www.obdadvisor.comEmail: [email protected]
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