OBD II P0440 Error Code Explained

By its full name OBD code p0440 is an indication, a symptom that something is happening to your vehicle’s EVAP system.

P0440 Code
P0440 Code

For those who don’t have so much experience in the mechanical field, EVAP stands for Evaporative Emissions, including components like fuel tank, gas cap, canister purge and vent solenoid, the storage carbon canister, and the fuel tank pressure sensor.

Other common codes:  P0441,  P0442,  P0456,  P0457,  P0455,  P0443,  P0446,  P0449, P0450,  P0451,  P0452,  P0453,  P0496

On short and in a simple formulation, this is the system that impedes fuel vapors to reach the atmosphere so p0440 is the code that alerts drivers that functioning properly with this system. And the functionality of this code indicating that something is happening with your vehicle doesn’t stop here. It can also be a sign that your car is experiencing a major leak.

How p0440 Is Detected

This particular code is signaled to drivers by the illumination of the Check Engine Light. If that weren’t the case and drivers wouldn’t receive such a straightforward signal they might not even be aware of some dysfunctional situation because in most cases no drive-ability problems appear.

There might be noticeable just a faint fuel odor coming from the EVAP system. This means that fuel vapors are released into the atmosphere instead of heading to the engine as they would normally do for creating the combustion process. So if this unparticular smell appears in your car don’t ignore it because it’s a symptom of the P0440 code.

The most common factors that make the Check Engine Light illuminate and attention drivers about this code are:

  • Improperly installed fuel cap,
  • absence of fuel cap or any other damages of this component,
  • the storage carbon canister is damaged/split or plugged,
  • the purge solenoid is failing,
  • the fuel tank presents a defection,
  • the evaporation vent/purge valves are defective,
  • the fuel tank sending unit gasket presents a defection,
  • and torn EVAP hose.

What to Do in Case of p0440

One simple thing to perform is to write down the freeze frame information, which is obtained after retrieving the code. This is for ensuring the baseline of any repairs that are going to take place.

The first solution and the most simple of all is to remove the fuel cap, to install it correctly and with care, clear the code and then after driving for a day check if the light illuminates again. If it does then the fuel cap is not damaged and it is correctly installed. So it’s time for another step implying a thorough inspection of the EVAP system for any holes, misplacement’s  or cuts in hoses. Other possible solutions might be the replacement of the purge valve or of the sensor.


These were only the simple solution that can be handled by everyone, not only a professional mechanic. To test for leaks drivers have to turn to a professional who will use a smoke machine to see if there are any. Or he will use specialized software to check the decaying rate for the vacuum. There is a leak when it decays much faster so it means that the p0440 is enforceable, which also leads us to the conclusion that sometimes is better to have professional people handling your vehicle. 

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