P0440 – Evaporative emission (EVAP) system -malfunction

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By Benjamin Jerew (Contact Me)
Last Updated 2016-03-30
ASE Master Tech
CodeFault LocationProbable Cause
P0440 Evaporative emission (EVAP) system -malfunction
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Hose connection(s), intake leak, EVAP canister purge valve

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Table of Contents

  1. What Does Code P0440 Mean?
  2. What are the common causes of code P0440 ?
  3. What are the symptoms of code P0440 ?
  4. How do you troubleshoot code P0440 ?
  5. Codes Related to P0440
  6. Get Help with P0440

What Does Code P0440 Mean?

In spite of the fact that fuel is delivered in liquid form, the internal combustion engine runs, not on liquid fuel, but on fuel vapors. This works out rather conveniently, since liquid fuel is far more easily manageable, but easily vaporizes into usable form, even when it’s below zero. The tendency of fuel to vaporize, called volatility, makes for good engine starting, performance, and efficiency. At the same time, fuel volatility creates another problem, evaporative emissions. Fuel vapors are carcinogenic and environmentally destructive, which is why fuel storage, at the refueling station on in your vehicle, is designed to significantly reduce evaporative emissions.


In your vehicle, the evaporative emissions control system, usually just referred to as the “EVAP” system, keeps fuel vapors from escaping into the atmosphere. Using a system of tubes and valves, the EVAP system routes fuel vapors from the fuel tank into an activated-charcoal canister for storage. At certain times, when the engine is running, the EVAP system will route fuel vapors from the canister to the engine, where they are burned. The ECM (engine control module) controls the EVAP system valves, monitoring system function via pressure sensors.


Many of the self-tests that the ECM performs on the EVAP system require that certain conditions be met first, such as sufficient battery voltage, specific fuel level, and specific atmospheric temperature. Aside from circuit tests, one of the first things that the ECM needs to verify is that the fuel tank and the rest of the system is sealed. To run this test, the ECM draws a vacuum on the tank. If the ECM detects that the EVAP system is unable to produce or hold a vacuum in a certain amount of time, it records a diagnostic trouble code (DTC) in memory, P0440, “Evaporative Emissions (EVAP) Control System Malfunction,” and illuminates the MIL (malfunction indicator lamp).

What are the common causes of code P0440 ?

Depending on year, make, and model, DTC P0440 may have number of causes. Here are some of the most common.

  • Gas Cap – This is, by far, the most common failure. Loose, missing, damaged, worn, or incorrect gas caps will not seal the system properly. Also, never refuel with the engine idling, as the ECM may elect to run the EVAP monitor at that time. Keep in mind that, if you tighten the gas cap after the MIL comes on, it will take 40 drive cycles for the ECM to clear the code on its own, unless you clear it with a scan tool.


  • Stuck Valve – If the canister close valve (CCV) or purge valve is stuck open, it will not seal the system. Depending on location, it can be contaminated or corroded, sticking open, even when not grounded by the ECM.
  • Canister Failure –
    • Because of its exposed position, the charcoal canister and associated tubes, hoses, and valves, are prone to damage.
    • Consistent “topping off the tank” has been known to saturate the charcoal canister with fuel, something which it was not designed for. Normally, the charcoal canister might weigh a couple of pounds, but a saturated canister might weigh up to 20 pounds.
    • An internally-ruptured canister, while external damage may be non-existent, may have allowed charcoal pieces to make it through to the engine intake, perhaps even sticking in the purge valve. Disconnect the EVAP purge line and look inside. If you see charcoal dust or pellets, you may have a ruptured canister.
  • Previous Repairs – If anything has been done on the vehicle, such as a tune-up, engine rebuild, timing belt, or EVAP system repairs, EVAP hoses or connectors may have been disconnected and reconnected. Make sure all electrical connectors, EVAP hoses, vacuum lines, and tubes are properly connected and sealed. Be wary of O-ring seals where plastic EVAP tubes connect to metal EVAP tubes.

What are the symptoms of code P0440 ?

Aside from the MIL, you will likely not notice any symptoms related to this EVAP system failure. Depending on the automaker’s failure mode, you may notice reduced fuel economy or engine performance.

How do you troubleshoot code P0440 ?

Because of the complexity of the EVAP system and the expense and availability of EVAP-specific diagnostic tools, you may be limited to a visual inspection of the system. Because of the nature of this DTC, you’re basically looking for anything that would prevent the system from sealing.

  • Other DTCs – P0440 often appears with other EVAP-related DTCs, such as P0441, P0442, P0446, etc. If any other EVAP DTCs are present, diagnose and repair those first. After repairing any other faults in the system, you can then proceed to diagnosing DTC P0440.
  • Gas Cap – Make sure the gas cap is installed properly and that it is an OE (original equipment) part. Check that the seal looks good, that is, smooth, flexible, no cracks or pitting. Make sure the fuel filler neck, where the gas cap seals, is also smooth. Make sure the gas cap torques properly, that the clutch sounds even or that single-click types feel firm. Replace as necessary. (At this point, you can usually clear the code and go on your way.)


  • Charcoal Canister – Inspect the charcoal canister for damage. Because of its exposed position on some vehicles, it may be damaged by road debris or dirt. Replace as necessary.
  • Tubes and Hoses – Similarly, make sure that all EVAP hoses and tubes appear intact and are connected properly. Cracked or disconnected hoses will not seal properly. Repair as necessary.
  • Valves – If possible, use a 12 V power source to bench-test the purge valve and the canister close valve. With voltage applied, you should be able to easily blow air through the valve. With no voltage applied, no air should pass through the valve. If the valve is corroded, damaged, or contaminated, it may stick open and will not seal the EVAP system properly. Clean or replace as necessary.
  • Fuel Tank – Check the fuel tank and fuel filler tube for damage. Repair or replace as necessary.
  • Pressure Testing – If you have access to the proper equipment, you can pressure test the EVAP system. Many vehicles have an EVAP test port under the hood, which you can use to pressurize the system, measure system pressure, and look for leaks. Keep in mind, however, that EVAP pressure testing should never go over 2 psi, otherwise you may damage the system. This should be done with the key off.
    • Disconnect or remove the purge valve. Air should not escape from the purge valve. Similarly, air should not escape from the canister close valve, which may be located under the hood or on or near the charcoal canister. Repair or replace as necessary.
    • Prepare a spray bottle of soapy solution, 50:50 dish detergent and water. Spray down EVAP connections, hoses, canister, fuel tank, or any other suspected leak area. Bubbles will form if you find a leak. Repair as necessary.

If you cannot find a problem, you may need to take it to a professional for more in-depth diagnosis.

  • P0441 Evaporative Emission Control (EVAP) System Incorrect Purge Flow
  • P0442 Evaporative Emission Control (EVAP) System Leak Detected (small leak)
  • P0450 Evaporative Emission Control (EVAP) System Pressure Sensor
  • P0455 Evaporative Emission Control (EVAP) System Leak Detected (gross leak)
  • P0456 Evaporative Emission Control (EVAP) System Leak Detected (very small leak)
  • P0457 Evaporative Emission Control (EVAP) System Leak Detected (fuel cap loose/off)
  • P0496 Evaporative Emission Control (EVAP) System High Purge Flow
  • P0497 Evaporative Emission Control (EVAP) System Low Purge Flow

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