Error P0440 – how to fix?

Code definition P0440

Evaporative emission control system malfunction

What does the code P0440 mean

P0440 is the generic OBD-II code meaning the engine control module (ECM) detects a leak in the fuel tank vapor system or the vapor pressure sensor has failed.

What causes the code P0440?

• The ECM has closed all the vapor lines in the fuel tank and monitors the vapor pressure and sees a pressure drop greater than allowed by the ECM’s test parameters.
• The cause of the code P0440 may be a loose gas cap which is the most common cause of the code.
• Code P0440 is also set if any component in the fuel vapor system is leaking such as the gas cap vent, vent valve, carbon canister, fuel filler neck, or any of the multiple fuel vapor recovery components.
• The fuel vapor pressure sensor is faulty, causing the ECM to read incorrectly.

What are the symptoms of the P0440 code?

• The Check Engine light will come on and the code will be stored in the ECM’s memory.
• You may notice the smell of fuel vapors in or around the vehicle if the vapor leak is large enough.

How does the mechanic diagnose the P0440 code?

• Scans codes and documents the code in the ECM. Looks at data from a frozen frame to see when a fault has occurred.
• Checks the entire fuel system, including fuel lines and vapor lines from the front to the rear of the vehicle, for any signs of fuel or vapor leakage.
• Checks for loose fuel cap as this is the most common problem.
• Performs a leak test on the fuel vapor system to try to locate the cause of a vapor leak through the test vapor port.
• If no leaks are present, then follow the manufacturer’s pinpoint test for a detailed steam sensor and system check for that code as these systems can be very different between manufacturers.

The most common errors when diagnosing the P0440 code

• Assuming a gas cap is leaking without thoroughly diagnosing the entire system.
• Not checking with the customer that the gas valve has not been loosened recently.

How serious is the P0440 code?

• The code P0440 illuminates the Check Engine light and this alone fails the exhaust emission test.
• The code means that the fuel vapor system has a vapor leak somewhere in the system and the vapor can be very flammable and dangerous to breathe the vapor.
• A loss of vapors in the system only means that the engine is not using them, and this can result in a loss of fuel mileage.

What repairs can fix the code P0440?

• Tightening or re-setting the fuel cap.
• Replace a leaking fuel cap that has a bad seal or a breather in the cap.
• Repair or replacement of leaking steam system components, such as an evaporation control valve or carbon dioxide absorber.

Additional considerations for code P0440

The code P0440 is one of the most common codes that will turn on the Check Engine light on vehicles today. The most common cause of this is that the fuel cap is left accidentally or is loose after refueling.