How do I fix P0440?

Alton Alexander
By Alton AlexanderUpdated on June 4th, 2022

P0440 is an OBD-II code for "Evaporative Emission Control System Malfunction". This code is triggered when the ECU detects a problem with the EVAP system. The EVAP system is responsible for capturing and storing fuel vapors from the fuel tank. These vapors are then drawn into the engine and burned, rather than being released into the atmosphere.

There are a few reasons why this code may be triggered. There may be a problem with the EVAP canister, the EVAP purge valve, the EVAP vent valve, or a leak in the EVAP system. A mechanic will need to diagnose the problem to determine the root cause.

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1. Check and replace the gas cap

  1. Open the hood and locate the gas cap. On some models, the gas cap is on the front of the car, while on others it may be on the back.
  2. On most cars, the gas cap is held in place by a spring-loaded clip. To replace the gas cap, first remove the clip by pushing down on one side and pulling the gas cap off.
  3. On some cars, the gas cap has a rubber gasket that must be replaced in order to ensure a tight seal. To replace the gas cap gasket, first remove the old gasket by peeling it off. Then, install the new gasket by pressing it down onto the lip surrounding the gas cap.
  4. Replace the clip by pressing it back into place and tightening the screw. Replace the gas cap by pressing it back onto the stem and rotating it until it snaps into place.

2. Check the EVAP system for leaks

The steps to check EVAP system for leaks are as follows:

  1. Remove the front and rear passenger side airbags.
  2. Remove the upper and lower front bumper cover.
  3. Remove the air intake ducts.
  4. Inspect the air filter and the intake manifold.
  5. Inspect the EVAP system for any leaks.
  6. If there are any leaks, fix them.

3. Check the purge solenoid

  1. Remove the purge solenoid by unscrewing the two screws located on the top of the solenoid.
  2. Inspect the inside of the solenoid for any debris or fluid. If there is fluid or debris, clean it up using a wet cloth.
  3. Reinstall the solenoid by screwing it back in place.
  4. Test the purge function by turning the key on and off several times. If the purge function works properly, the check engine light should now be off.

4. Check the vent solenoid

  1. Turn off the car and open the hood.
  2. Locate the vent solenoid and remove the screws that hold it in place.
  3. Carefully remove the solenoid and inspect it for damage. If there is damage, replace the solenoid.
  4. Reinstall the solenoid and screws, and turn on the car. If the problem is fixed, the car will start without the need for the key.

5. Check the canister

  1. Remove the connector from the fuel rail.
  2. Remove the screws that hold the canister in place.
  3. Remove the canister.
  4. Check the sealant around the threads of the canister. If it is cracked or missing, replace the canister.
  5. Reinstall the canister and screws in the correct order.
  6. Connect the connector to the fuel rail.

6. Check the fuel tank pressure sensor

  1. Park the car in a level place.
  2. Place the car in Park and hold the brake pedal down.
  3. Turn the ignition OFF.
  4. Disconnect the negative battery cable.
  5. Open the fuel tank cap.
  6. Check the fuel pressure reading with a gauge.
  7. If the pressure is higher than 10 psi (70 kPa), replace the fuel tank pressure sensor.
  8. Connect the negative battery cable and close the fuel tank cap.
  9. Turn the ignition ON.
  10. Release the brake pedal.

Some users might also have success with the following opitons:

  1. Check the EVAP system hoses
  2. Clean the EVAP system
  3. Replace the purge solenoid
  4. Replace the vent solenoid
  5. Replace the canister
  6. Replace the fuel tank pressure sensor