P0440 – Meaning, Causes, Symptoms, & Fixes

Code P0440 Definition

Evaporative Emission Control System Malfunction

Code P0440 Meaning

The evaporative emission control (EVAP) system prevents fuel vapors from escaping into the atmosphere. When the vent control valve opens, the fuel vapors from the fuel tank travel through a vent line to the charcoal canister. The fuel vapors are then absorbed and stored by activated charcoal pellets in the charcoal canister. On the charcoal canister is a purge valve. When the purge valve is opened, the vacuum from the engine draws the fuel vapors out of the charcoal and into the engine intake manifold where it is then used as part of the air-fuel mixture needed for combustion within the cylinders of the engine. Vehicles’ fuel tanks since the 1990’s have been pressurized to reduce the amount of fuel evaporating into the atmosphere. However, when code P0440 is set, a leak has been detected in the Engine Control Module (ECM) or a vapor pressure sensor has malfunctioned.


  • Check Engine Light
  • Fuel vapor odor


  • Loose or damaged gas cap
  • Leaking or disconnected EVAP hose
  • Faulty purge valve
  • Faulty canister vent valve
  • Charcoal canister leak
  • Leaking fuel tank

Code P0440 Severity – Low   

Code P0440 will not cause any noticeable driving issues but will result in a failed emissions test. These vapors are extremely flammable and dangerous to breathe in as well.

Code P0440 Common Diagnosis Mistakes

Replacing the gas cap without checking any parts of the fuel vapor system.

Code P0440 Diagnosis Steps

How To Diagnose P0440

  1. Inspect your gas cap to see if it is loose or damaged
    1. If your gas cap is loose, tighten it and clear the code.
    2. Inspect your gas cap for physical damage or deterioration. However, it should be noted that damage to the gas cap or deterioration of its components are not always noticeable. If your gas cap was not loose and you do not see any indications of failure, try replacing the gas cap anyways and clearing the codes. Gas caps are relatively inexpensive and are often the fix for code P0456.
  2. Check for cracked or disconnected EVAP hoses near or connected to engine air box
    1. Replace cracked/disconnected hoses
    2. Clear code
  3. Inspect the fuel tank and charcoal canister for damage and leaks. Replace if necessary.
  4. If you have not been able to find the problem in the previous steps, you will need to check your purge valve (solenoid) to make sure that there are no leaks within that system.
    1. You will be using your vacuum pump gauge to test your purge valve
    2. How-to test your purge valve can be found in your car’s service manual or a Hayne’s Repair Manual to find more information on car specific testing procedures. Below (Step 5) is a general guideline.
  5. How to Test Purge Valve:
    1. Disconnect the vent line connected to the purge valve. The vacuum pump gauge will be connected to the purge valve in place of the vent line.
    2. Pump the vacuum pump gauge to 17 psi. When the vacuum is applied the valve should hold the vacuum and not leak.
    3. If the vacuum drops (the needle on the pump gauge moves), the valve should be replaced.
    4. Apply battery voltage to the purge valve. You should hear an audible click as the purge valve opens, and the pressure on the vacuum pump gauge should drop. If it does not open, the purge valve is faulty and must be replaced.

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Comments 14

Roger Fox

June 25, 2018

My mechanic has gone through all the tests leaving only the pressure sensors left as the problem. In my car they are located atop the fuel tank and the tank has to be lowered to replace the sensor. I am presently attempting to prove this diagnosis by clearing the code, filling the tank and driving until the engine light comes on. There are two sensors associated with the pressure that should be in the tank at half full and one at quarter full. If the light comes on at 1/2 it is the sensor that measures 1/2 tank pressure. If it comes on at 1/4 tank then it is the other sensor.

Richard Heller

September 29, 2018

How do I clear the code after I replace the gad vap?


October 25, 2018

Unhook the battery.

Sherry D Ross

December 14, 2018

If you have the FIXD app on your phone there is a clear code button to click on. It will clear the code.


October 26, 2018

How to clear code of PO440?


November 10, 2018

A code reader has the option the clear it. I got one for $20 at Walmart.


February 4, 2019

Ever since I got this code I noticed a humming sound near rear of vehicle after idling for a few minutes, is this something to do with my code issue?

Thayne Heath

July 23, 2019

Could be air compressor if your vehicle has one for the shocks.


August 7, 2019

Could be the fuel pump


February 25, 2019

Mine is doing the exact same thing. Has the humming sound as well. Did you figure out what your issue was?


March 18, 2019

could be the fuel pump..


May 1, 2019

For that humming sound,it could be that the gas cap is sucking air


May 5, 2019

Bad fuel filter. Makes your fuel pump work harder. You Won’t hear a gas cap leaking air.. But a factory fuel pump that’s whining is a restriction. Change fuel filter AND fuel pump Relay. And or your to low on fuel. 39 years experience and counting. But I don’t know everything.. That’s why I’m here.. Thanks


August 7, 2019

It’s the fuel pump

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