P0440 – Evaporative Emission System

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. P0440 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 severe, you’ll need to fix it before your next emissions test. Please read below for more details about this code, what it means, and how to clear it from your system.

P0440 Code Definition

Evaporative Emission Control System Malfunction.

Here's where you can get a thorough understanding of the P0440 OBD2 code
If you want to learn about the P0440 OBD2 code, this is the right place

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 system’s sensors has malfunctioned. 

The EVAP system’s role in your plan 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.

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

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

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?

  • The gas cap is damaged or loose (most common cause)
  • Hoses in the EVAP system are leaking, damaged, or disconnected
  • Purge valve or purge solenoid is faulty
  • The vent valve is faulty
  • The charcoal canister is leaking
  • The 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 severe. 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, which 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 into “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 needs replacing.
  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 ensure 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 step 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 the damage. It is the most likely cause of the P0440 trouble code. Since gas caps are relatively 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 whole 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 their 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: P2002 Code: Meaning, Symptoms, Causes, Diagnostics, And Fixes