P0440: Evaporative Emission Control System Malfunction

What is P0440?

Code P0440 is defined as “Evaporative Emission Control System Malfunction.” 

This generic OBD-II (OBD2) code means that the engine control module (ECM) has detected a leak in the EVAP system or that a fuel vapor pressure sensor (also called the fuel tank pressure sensor) has malfunctioned.

The evaporative emission control (EVAP) system captures harmful fuel vapors from escaping into the environment. When specific engine conditions (engine speed, temperature, etc.) are met, these fuel vapors are cycled back into the combustion process. 

How the EVAP System Works

Fuel vapors from the gas tank travel through a vent tank line* to a charcoal canister (also known as the carbon canister or vapor canister). Activated charcoal pellets in the vapor canister absorb and store the fuel vapors. 

The EVAP canister purge valve controls how much fuel vapor is allowed into the engine and is usually closed. When the ECM commands it to open, the intake vacuum from the engine draws the fuel vapor from the charcoal canister and into the engine intake manifold. Here, it becomes part of the air-fuel mixture used for combustion within the engine cylinders.

The canister vent valve is usually open, allowing air to flow into the canister. It’s closed when the  ECM pressurizes the system to run checks for vapor leaks. 

If the ECM detects inconsistencies in the EVAP system, it generates engine code P0440 and triggers the check engine light.

*Note: An EVAP vent line is similar to a fuel line, except with a smaller diameter.

P0440 Symptoms

Error code P0440 will usually manifest itself in the following ways:

1. Check Engine Light is On

The check engine light is one of the first indicators of potential problems with your car’s EVAP system. 

The ECM uses the fuel tank pressure sensor to identify a leak within the EVAP system and triggers the check engine light when something’s wrong. This could be a small leak or otherwise.

However, a lit engine light is a generic indicator for many engine issues, so you’ll need a scan tool to verify if this EVAP code is one of them.

2. Fuel Smell Caused by a Fuel Vapor Leak

The ECM triggers OBD-II code P0440 when there’s a leak within the EVAP system or if the EVAP system’s fuel tank pressure sensor malfunctions. 

If there’s a vapor leak, you may smell fuel vapor (a gasoline-like smell) from the engine. You may also notice reduced gas mileage. This indicates potential problems with the fuel vapor system, and you should consider getting a smoke test done. A smoke test will help identify where the leak is.

P0440 Causes

DTC P0440 can result from various issues tied to the EVAP system. Some possible triggers for this fault code include:

• Missing or loose gas cap (fuel cap)
• Incorrect fuel cap used
• Foreign matter caught in the fuel cap or fuel filler neck
• Damaged fuel filler neck
• Bad fuel vapor pressure sensor
• Damaged purge valve (purge solenoid) or vent valve
• EVAP canister leak
• EVAP hose leak
• Leaking gas tank

Can I Still Drive With a P0440 Code?

You can technically drive with this error code, but it’s not recommended.

While error code P0440 typically doesn’t immediately impact vehicle functionality, it does indicate the likelihood of harmful, flammable vapors being released into the environment. Exposing the driver and passengers to these vapors can be dangerous and detrimental to health. 

Additionally, the P0440 code will turn on the check engine light — resulting in a failed emissions test.

Diagnosing P0440

Diagnosing engine code P0440 requires a thorough inspection of the EVAP system, so it’s not recommended as a DIY. 

That said, here are steps a mechanic would take to diagnose trouble code P0440: 

1. Start by connecting an OBD-II scan tool to the engine and checking for other evaporative emission system codes. Capture the freeze frame data to identify code P0440.

2. Inspect the fuel cap to make sure it isn’t loose or damaged. If the fuel cap is loose, tighten it and clear the trouble code to see if it gets resolved. 

3. Check for an EVAP system leak through a smoke test. Pressurize the EVAP system with an EVAP smoke machine to see if the smoke leaks from any vapor lines, hose, seal, or gasket.

4. Check that the EVAP purge valve and vent valve can hold a vacuum for a sustained time (for 30 to 60 seconds). If either fails, it’ll cause a vacuum leak, meaning the system won’t hold a vacuum properly.

Possible Repairs for P0440 & Costs

The P0440 error code may sometimes require a combination of one or more repairs. This is why it’s crucial to fully diagnose all possible causes for this EVAP code before replacing car parts. 

Here are some possible solutions, depending on the cause:

• Tighten a loose gas cap 
• Replace or repair sealing in the gas cap
• Replace the EVAP purge control valve
• Fix wirings to the EVAP purge control valve
• Replace damaged EVAP vapor lines or hoses
• Replace the fuel tank (gas tank)
• Replace charcoal canister (rare)

Repair costs:

Repair costs for DTC P0440 vary widely based on the root cause. It typically costs anywhere between $100-$600, including labor charges and the cost of parts. 

Here are some estimates of the various repair solutions for P0440: 

• Gas cap: $20 – $60
• EVAP line: $50 – $100
• EVAP purge valve: $150 – $200
• EVAP canister: $200 – $600