P0440 OBD-II Trouble Code: Evaporative Emission Control System Malfunction

Check Engine Light

P0440 code definition

Evaporative Emission Control System Malfunction

What the P0440 code means

P0440 is an OBD-II generic code that the engine control module (ECM) has detected a leak in the fuel tank vapor system or a vapor pressure sensor has malfunctioned.

What causes the P0440 code?

  • The ECM has closed off all of the fuel tank vapor lines and monitors the vapor pressure and sees a pressure drop more than is allowed within the test parameters of the ECM.

  • The cause of code P0440 can be a loose gas cap which is the most common reason for the code.

  • Code P0440 is also set if any component in the fuel vapor system is leaking like a gas cap vent, vent valve, carbon canister, fuel filler neck, or any of the many fuel vapor recovery components.

  • The fuel vapor pressure sensor is faulty causing an incorrect reading input to the ECM.

What are the symptoms of the P0440 code?

  • The Check Engine Light will be illuminated and the code is set in ECM memory.

  • You may notice a fuel vapor odor in or around the vehicle if vapor leak is large enough,

How does a mechanic diagnose the P0440 code?

  • Scans codes and documents the code in the ECM. Views the freeze frame data to see when fault happened.

  • Inspects the entire fuel system to include the fuel lines and vapor lines from the front to the rear of the vehicle for any signs of fuel or vapors leaking.

  • Checks to make sure the fuel cap is not loose as this is the most common problem.

  • Performs a smoke leakage test on the fuel vapor system to try and locate the cause of the vapor leak using the test vapor port.

  • If no leaks are present, then follow the manufacturer pinpoint test for detailed checking of the vapor sensor and system for this code since these systems can be very different between manufacturers.

Common mistakes when diagnosing the P0440 code

  • Assuming the gas cap is leaking without doing a thorough diagnostics of the complete system.

  • Failing to check with the customer to see if the gas cap was left loose recently.

How serious is the P0440 code?

  • Code P0440 causes the Check Engine Light to go on and this alone will cause a failed emission test.

  • The code means the fuel vapor system has a vapor leak somewhere in the system and vapors can be very flammable and dangerous to breath the vapors.

  • The loss of vapors in the system only means the engine did not use them and this may cause a loss of fuel mileage.

What repairs can fix the P0440 code?

  • Tightening or resetting the fuel cap.

  • Replacing a leaking fuel cap that has a bad seal or vent in the cap.

  • Repairing or replacing leaking vapor system components like a vapor control valve or carbon canister.

Additional comments for consideration regarding the P0440 code

Code P0440 is one of the most common codes that causes the Check Engine Light to come on in vehicles today. The most common cause for this is the fuel cap being accidently left off or not tightened securely after getting fuel.

Need help with a P0440 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

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