Auxiliary Emissions ControlOBD2 Codes

P0440 – Meaning, Causes, Symptoms, & Fixes

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Code P0440 Definition

Evaporative Emission Control System Malfunction

What Does P0440 Mean?

The evaporative emission control (EVAP) system prevents fuel vapors from escaping into the atmosphere. When the vent control valve is open, 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. The purge volume control valve controls how much fuel vapor is allowed into the engine. When it is opened (it is normally closed), the vacuum from the engine draws the fuel vapors out of the charcoal canister 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 1990s, have been sealed in this way to reduce the amount of fuel evaporating into the atmosphere. However, when code P0440 is set, a leak has been detected by the Engine Control Module (ECM) or a vapor pressure sensor has malfunctioned. The ECM determines this when the vehicle is turned off, and the vent control valve is commanded closed. At this point, the ECM monitors EVAP system pressure, and if it doesn’t maintain pressure, it will trigger the Check Engine Light.

What Are The Symptoms Of Code P0440?

  • Check Engine Light
  • Fuel vapor odor

What Is The Cause Of Code P0440?

  • Missing, defective, damaged, or loose gas cap (*Most Common)
  • Leaking or disconnected EVAP hose
  • Faulty purge volume valve
  • Faulty canister vent control valve
  • Charcoal canister leak
  • Leaking fuel tank

How Serious Is Code P0440? – Low


Code P0440 will not cause any noticeable driving issues but will result in a failed emissions test. However, as with all check engine light diagnostic trouble codes, you should repair it as soon as possible to return the vehicle to normal operation.

Code P0440 Common Diagnosis Mistakes

Many people fail to perform a smoke test before or after replacing the fuel cap and jump straight to component replacement. The problem could be as simple as a loose or cracked EVAP hose.

Tools Needed to Diagnose:

  • FIXD
  • Basic hand tools
  • Vacuum gauge (optional)
  • EVAP smoke machine leak checker
  • Fused jumper wires
  • Vehicle specific service manual

How To Diagnose And Repair Code P0440:

Difficulty of Diagnosis and Repair – 2 out of 5

  1. Inspect your gas cap to see if it is loose or damaged. If your gas cap is loose, tighten it and clear the code. 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 anyway and clearing the codes. Gas caps are relatively inexpensive and are often the fix for code P0440.
  2. If the fuel cap didn’t fix it, perform an EVAP system leak check: Pinch off the vent tube to the EVAP Vent Control Valve. Pressurize the EVAP system with an EVAP smoke machine leak checker. Check to see if you see any smoke leaking out from any hoses or seals. If there are any leaks, repair leaks, clear the check engine light, and check to see if the concern is resolved.
  3. If the code returns, test the Purge Volume Control Valve for a Stuck Open condition. With the key and engine off, remove the hose going to the Purge Volume Control Valve coming from the fuel tank and unplug the electrical connector to the valve. (performing this test may set another code if it does, clear the code and disregard it until after the test is completed and the vehicle is put back together). (Tech Tip- The EVAP purge volume control valve is usually located on or near the intake manifold.) Now, start the engine and use either a vacuum gauge or your finger to see if the vacuum is coming out of the Purge Volume Control Valve where you removed the hose. If there is a vacuum, then the Purge Volume Control Valve is leaking and needs to be replaced. If there is no vacuum, you could still have an intermittent failure of the Purge Volume Control Valve or another EVAP system issue. Continue the diagnosis on the next step.
  4. If the purge valve passes the test, check the EVAP vent control valve for proper operation. This valve can get sticky, have debris caught in it, or the internal solenoid can fail and not operate. To test: Remove the EVAP vent control valve from the vehicle. (Tech Tip- The EVAP vent control valve is usually located under the car in the rear of the vehicle by or attached to the charcoal canister.) Verify with no power or ground supplied that you can blow through the valve’s openings. (If you can’t blow through the openings, the valve is stuck closed and needs to be replaced.) Now, supply power and ground to the solenoid (reference the service manual for your vehicle to find out which pins to supply power and ground to) the valve should click, and now you shouldn’t be able to blow through the openings. If you can blow through the valve when it is powered on, then the valve is faulty and needs to be replaced.*

*If the code returns, you will need to be given further diagnostics by a mechanic. More diagnostic steps could require electrical testing of the purge and vent control valves for proper operation.

Estimated Cost of Repair

For error code P0440, one or more of the below repairs may be needed to solve the underlying issue. For each possible repair, the estimated cost of repair includes the cost of the relevant parts and the cost of labor required to make the repair.

  • Gas Cap $20-$60
  • EVAP Line $20-$100
  • EVAP Vent Control Valve $150-$200
  • Purge Volume Control Valve $150-$200


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  1. 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.

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

    1. Unhook the battery.

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

      1. Yes, it was very helpful.

  3. How to clear code of PO440?

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

    2. FIXD can clear the code !

  4. 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?

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

    2. Could be the fuel pump

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

    1. could be the fuel pump..

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

    3. 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

  6. It’s the fuel pump

  7. I removed the hose going in to the PCV valve coming from the charcoal canister and disconnected the power source (connector); I did this with the engine off (no key in the ignition). I then turned the car on and put my finger on the open end of the PCV valve and felt a vaccuum, from what I understand this indicates a faulty PCV valve (stuck open) and should be replaced, correct?

    I have problem code P0440, assuming the PCV valve is the culprit why have I not experienced the usual symptoms of a (stuck open) PCV valve? I don’t have a rough idle or any misfires. Someone did mention smelling a faint hint of fuel vapor inside the cabin (while the AC was on) and I think I am getting less gas mileage but not sure.

    2005 Mercedes E500

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