P0440 Code: Evaporative Emission Control System Malfunction

Obd2 Trouble Code

A P0440 Code appears in your engine control module when it recognizes a malfunction with the EVAP system.

This trouble code is often not as bad as you think. In this article, we will teach you how to get rid of it.

P0440 Definition

Evaporative Emission Control – System Malfunction

What does the P0440 mean?

The P0440 means that there is a leak or malfunction in the EVAP emission system.

The EVAP system is a sealed gas vapor system that pulls the fuel vapors from the gas tank and combusts them through the engine instead of releasing them into the air.

P0440 Symptoms

You will likely not experiencing any symptoms, except the Check engine light on your dashboard. In some rare cases, you may experience a gasoline smell and a slight change in fuel consumption.

  • Gasoline Smell
  • Check Engine Light
  • Slightly decrease in fuel consumption

How serious is the P0440 Code?

Very Low – Your car engine won’t experience any further damage from the P0440 code.

In rare situations, the car engine can run slightly leaner, but it is nothing that will affect its performance.

Causes of the P0440 Code

The most common cause of the P0440 code is that you didn’t shut off your car at the gas station and let it run without the fuel cap tightened. Problems with the EVAP purge control valve are also common.

  • You let your car run at the gas station without the fuel cap on.
  • Faulty gas cap
  • Faulty EVAP purge control valve
  • Damaged fuel tank
  • Damaged Canister
  • Clogged or leaking EVAP pipes

What repairs can fix the P0440 code?

  • Tighten the gas cap & remove trouble codes
  • Replace or replace sealing in the gas cap
  • Replace EVAP purge control valve
  • Fix wirings to EVAP purge control valve
  • Replace fuel tank
  • Replace Canister
  • Replace damaged EVAP pipes/lines

Common P0440 Diagnostic mistakes

A widespread diagnostic mistake with the P0440 code is to start too advanced troubleshooting. There is a high chance that there is no problem with the EVAP system – someone maybe just forgot to shut off the car engine while refueling the car or forgot to tighten the fuel cap properly after refueling.

This trouble code is also very similar to the P0442 code.

How to diagnose the P0440 Code

  1. Connect a Diagnostic Scanner and check for any related trouble codes. Make sure the trouble code is not stored by mistake while refueling.
  2. Check so the gas cap is tightened properly and that the sealing is fine.
  3. Check the EVAP purge solenoid. Ensure the line is sealed when it is closed, and make sure it’s working by testing it with 12 volts and ground.
  4. Check if the ECU is sending any signal to the EVAP purge solenoid. Find a more in-depth guide of how to do it here: P0445.
  5. Pressurize the pipe going towards the fuel tank. Use an EVAP smoke machine to find the leak if you suspect that there is a leak.
  6. If the system is sealed and the purge control solenoid works – Remove the trouble codes and let the customer try the car for a couple of days.

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Written by: Magnus Sellén

Founder, owner & main author of Mechanic Base. I have been repairing cars for more than 10 years, specialized in advanced diagnostics & troubleshooting. I have also been a drifting driver and mechanic for over 7 years.