#OBD Codes
P0440 – Evaporative emission control system malfunction
Technical definition
EVAP emission control system malfunction
What does P0440 mean?
The P0440 code means your car has found a problem with its evaporative emission control (EVAP) system. Simply put, it means a fuel vapor leak or a faulty pressure sensor in the EVAP system.
What is the EVAP system?
The EVAP system keeps harmful fuel vapors from escaping into the air. It captures vapors from the fuel tank and stores them in a charcoal canister until the engine can safely burn them.
To do this job, the EVAP system relies on three main components:
- Vent valve: Manages system pressure by allowing fresh air in when the purge valve opens
- Purge valve: Controls the flow of fuel vapors into the engine
- Sensors: Monitor fuel tank pressure to ensure everything is working correctly
The figure below shows how these components interact to manage fuel vapors and maintain the system’s efficiency:
The basic scheme of self-testing EVAP system
Your car’s ECU regularly checks the EVAP system by closing the vent and purge valves to see if it can hold pressure. If it detects a leak, it triggers the P0440 code. This code often comes with other EVAP-related codes that help pinpoint the exact issue.
Can I still drive with P0440?
You can continue driving without immediate concern.
However, leaving the issue unchecked means your check engine light remains on, which is not only annoying but could also obscure more serious problems that may arise.
In addition, leaks in EVAP system allow fuel vapors to escape into the atmosphere and your cabin. Prolonged exposure to these vapors harms the environment and can cause headaches, dizziness, and breathing issues.
Symptoms of P0440
You probably won't notice any performance issues with the P0440 code. However, you'll see the check engine light on your dashboard and likely smell a fuel odor in the cabin or around the car.
Common causes of P0440
Most often, the P0440 appears due to leaks in the EVAP system, such as:
- A loose gas cap
- A cracked charcoal canister
- Punctures or cracks in vacuum or fuel vapor hoses
Malfunctioning EVAP system components can also trigger this fault code:
- A malfunctioning EVAP pressure sensor
- A malfunctioning purge valve
- A malfunctioning or clogged vent valve
How to troubleshoot P0440
Use these tips to diagnose and fix the P0440 code accurately:
Scan for other codes
Start by using an OBD scanner to check for other related trouble codes. These can provide more context about the issue. Some of the related codes to look out for include:
Clear the codes and test drive
Use your OBD code reader to clear the P0440 fault code from your car.
- If the fault code immediately reappears: The issue is still active. Skip the test drive and continue diagnosing.
- If the codes clear successfully: Take your car for a 15-minute drive to warm up the engine and see how it behaves.
After your test drive, scan again to see if the code returns. If it does, you've confirmed a persistent problem that needs fixing.
Check the gas cap and seals
One of the most common reasons for EVAP system leaks is as simple as a loose or damaged gas cap.
Make sure the gas cap is tight and undamaged. Then, inspect the rubber O-ring for cracks or wear and replace it if necessary. If dirt surrounds the gas cap, spray it with WD-40 and wipe it away.
Use a smoke machine
A smoke test is an effective way to find leaks in the EVAP system. Smoke visibly escapes from cracked EVAP hoses, cracks in charcoal canister, holes, or loose connections, making it easier to identify the issue's exact location.
Examine vent and purge valves
If you don’t find any leaks, focus on the valves. Ensure the vent and purge solenoid move freely and aren't stuck, and clear any debris blocking it. Also, look for a blocked EVAP vent path, pinched vent hose, or damaged EVAP vent housing.
Finally, check the electrical circuit closely – there might be signs of damage or loose connections in the wiring.
Disclaimer: Advice, how-to guides, and car care tips on our blog are intended as helpful resources for general maintenance and repairs. While we strive for accuracy, the information is provided to the best of our knowledge and should be used at your own discretion and risk.
Always refer to your vehicle's owner's manual or consult a certified mechanic for specific repair details and safety procedures.
Always refer to your vehicle's owner's manual or consult a certified mechanic for specific repair details and safety procedures.
