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P0440 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Definition

Code P0440 represents an evaporative emission control system malfunction. This code will appear if your EVAP system is not working correctly. The EVAP system is what stores the fuel while it is expanding in the hot weather until it is sucked into the engine and burned.

In order to do this, the car manufacturers put a charcoal cannister in the engine compartment and install hoses between the cannister and the fuel tank.

When there are too many fumes to fit in the gas tank, they then travel in the hoses until they can be used as fuel. If one of these hoses or the valve that lets the fumes go into the engine malfunctions, then gas fumes will go into the air. This isn’t good for anyone, so this OBD2 code will appear.

Meaning

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

Causes

There are a few reasons behind why this code could appear. It could be that the ECM has closed off all of the fuel tank vapor lines. The ECM monitors the vapor pressure, and if it sees a pressure drop more than is allowed within the test parameters of the ECM, it will show this code.

Another reason for this code could be a loose gas cap. This is the most common reason for the P0440 code.

Code P0440 will also appear if any component in the fuel vapor system is leaking. This could be a gas cap vent, vent valve, carbon canister, fuel filler neck, or any of the many fuel vapor recovery components.

The last possibility behind this code is that the fuel vapor pressure sensor is faulty, which will cause an incorrect reading input to the ECM.

Symptoms

The symptoms of this problem are pretty easy to see. 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.

Diagnosis

To verify the problem, scan codes and document the code in the ECM. Then, view the freeze frame data to see when the fault happened.

Inspect 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.

Check to make sure the fuel cap is not loose, as this is the most common problem.

Perform 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

There are a few ways in which correcting a P0440 code can go wrong. Assuming the gas cap is leaking without doing a thorough diagnostics of the complete system will cause serious problems. Also, you should always remember to check with the customer to see if the gas cap was left loose recently. This could solve the problem very quickly.

How serious is this?

Code P0440 causes the Check Engine Light to go on, and this alone will cause a failed emission test. This is a pretty serious issue.

The code means the fuel vapor system has a vapor leak somewhere. This needs to be fixed immediately because vapors can be very flammable and also dangerous to breath in.

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 code?

Luckily, there are a few repairs which can fix code P0440. Tightening or resetting the fuel cap is an obvious one. You can also replace a leaking fuel cap that has a bad seal or vent in the cap.

Lastly, you can repair or replace leaking vapor system components, like a vapor control valve or carbon canister.

Related codes

Some related codes include P0441, P0442, and P0443.

Conclusion

The P0440 code is not something that should be ignored. If left untreated, it can cause serious damage to the vehicle.

Thankfully, there are several repairs you can try and there is a set list of ways you can determine the cause of the code. You should be able to fix this error code right away, without issues. If you have tried these repairs and you still do not have any luck, there may be a more serious problem.