What Is Engine Code P0440?

  • P0440 Technical Definition: Evaporative Emission Control System Malfunction
  • P0440 Meaning: A possible fuel vapor leak or FTP sensor problem
  • Most common cause: Faulty fuel cap
  • Risks for the engine/driver: LOW You should get it checked out ASAP but your car should be safe to drive
  • Emissions severity: HIGH. The car probably won’t pass emissions testing
  • Estimated repair time: 1 Day
  • Estimated repair cost: $100+

The engine code P0440 is stored in memory when the ECU detects a malfunction in the Evaporative Emission System (EVAP).

The EVAP is an integral part of the emissions control system, its role is in preventing fuel fumes from reaching the atmosphere. These gases are the normal result of fuel evaporating inside the tank. The EVAP system consists of a sealed container (the fuel tank) that works in conjunction with one or more charcoal canisters.

These canisters purge the gases back to the engine when the ECU consider it appropriate. Besides controlling the EVAP purge and vent solenoids the Electronic Control Unit has a dedicated fuel tank pressure sensor (FTP sensor) and in some vehicles a leak detection pump.

The FTP sensor is constantly informing the ECU about the fuel vapor pressure in the tank, but also is a key component during the occasional leak tests performed by the ECU. 

The code P0440 is set when the ECU detects a leak in the EVAP system during these tests or when the FTP sensor is not responding as expected. 

2 Common Symptoms When Code P0440 is Present

  1. Check Engine Light 
  2. Gasoline smell coming from the vehicle

Possible Causes For Error Code P0440

The most common causes of data trouble code P0440 are:

  • Aftermarket gas cap that doesn’t meet OEM specifications.
  • Improperly closed gasoline cap.
  • Faulty gas cap.
  • Burnt, damaged, broken or deteriorated EVAP hose.
  • Defective fuel tank pressure sensor
  • Defective leak detection pump
  • Defective fuel tank seal.
  • Defective EVAP canister.

How To Diagnose The Engine Code P0440

For the purpose of this article, it’s assumed that you have a basic knowledge of safety precautions while working on your vehicle.

Always refer to the appropriate OEM literature when possible. Original manufacturer diagnostic procedures should always have precedence over a generic workflow.

That said, let’s start the diagnostic process!

1. Preliminary steps

To discard a possible intermittent DTC condition, you’ll need to clear the ECU memory and complete a driving cycle.

  • Read data trouble codes and take note of them.
  • Clear data trouble codes memory.
  • Perform a driving cycle (at least 5-10 minutes).

In case the Check Engine Light stays off then you may have an intermittent problem. If the light lit during your driving cycle then continue with the diagnostic process.

2. Visual Inspection

> Gas Cap inspection: perform a meticulous visual inspection of the gasoline cap. Check its seal condition. Change as needed. Double check the part number and pressure specifications. Modern gas caps have similar specifications than radiator caps, using the incorrect part can bring the same issue.

> EVAP hoses: perform a meticulous visual inspection of all Evaporative Emission system hoses. These hoses come from the fuel tank all the way through the EVAP canisters and then from the canister they go to the intake manifold. Check for loose clamps, deteriorated hoses, etc. Don’t overlook this step. Many times the code P0440 is caused by a large leak in one of these hoses.

Fix any wiring problem before continuing.

3. Scan Tool Tests

> Fuel Tank Pressure sensor test: for this test, you will need to access the fuel pump assembly. Depending on your vehicle this could be as easy as removing the rear seat row but in some cases, you may need to remove the fuel tank which isn’t an easy task. Please keep that in mind before starting the test. Assuming you have access to the sensor, remove it from the fuel pump assembly. This sensor is like the Manifold Absolute Pressure sensor (MAP). Turn the ignition key on (engine off). Using the relevant adapter connect a manual vacuum pump to the sensor port.

Now you can increase the pressure (positive pressure) or create a light vacuum using the manual pump. With the help of a scan tool, watch the sensor output as you vary the pressure. If no change is detected then you should check the wiring from the sensor to the ECU. This is an analog sensor, start verifying the 5V reference voltage and ground. An alternative method that doesn’t require accessing the fuel pump assembly is disconnecting one of the fuel vapor vent lines. You can pressurize/depressurize the tank through that hose using a manual vacuum pump. Never use compressed air for this task because is highly dangerous.

> EVAP solenoids functional test: start the engine to enter KOER mode. Depending on the year and maker of your vehicle you may have access to EVAP functional tests. The functional test consists in opening/closing the EVAP purge. If the solenoids are not working then you should check the wiring, connector, relay, and fuse.

> EVAP leak detection pump functional test: start the engine to enter KOER mode. Depending on the year and maker of your vehicle you may have access to EVAP functional tests. This functional test consists of operating the EVAP leak detection pump. If the pump is not working then you should check the wiring, connector, relay, and fuse. Replace as necessary.


How To Repair Error Code P0440

Depending on the diagnostics results you may need to do the following:

  • Replacing the fuel cap.
  • Replacing the fuel tank seal.
  • Replacing or repairing the EVAP hoses.
  • Replacing the fuel tank pressure sensor (FTP)
  • Replacing the EVAP leak detection pump
  • Replacing or repairing the purge solenoids, relay or fuse.

Here's a video that explains a possible fix for P0440 and P0443

Even when this code doesn’t affect engine’s performance you need to be aware of legal issues when driving in zones with strict emissions regulations.

A fuel vapor smell will instantly make you fail emissions regulations, and may be dangerous to your health.