P0440: Evaporative Emission Control System Malfunction

What Is P0440?

Code P0440 refers to an “EVAP or Evaporative Emission Control System Malfunction.” 

This generic OBD-II (OBD2) code appears when the engine control module (ECM) detects a leak in the EVAP system (Evaporative Emission Control System). 

It also results from a damaged fuel vapor pressure sensor (also called the fuel tank pressure sensor) sending inaccurate information to the ECM, making it seem like there’s a problem even though there’s no leak. 

What Does the EVAP System Do?

The EVAP system prevents harmful fuel vapors from escaping into the environment and recycles them back into the engine’s intake system for combustion.

Here’s how the 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 enters the engine. When the ECM signals it to open, the engine’s intake vacuum draws the fuel vapor from the charcoal canister (through the vacuum line) into the engine intake manifold. It becomes part of the air-fuel mixture used for combustion within the engine cylinders.

The canister vent valve plays a crucial role in the vehicle’s EVAP system. It typically remains open to allow air to flow into the charcoal canister. This continuous airflow helps the system maintain proper pressure and function.  The valve closes when the ECM pressurizes the system to check for vapor leaks. 

If the ECM detects an EVAP system issue, it generates engine code P0440 and triggers the check engine light (CEL)

Note: EVAP vent lines are similar to fuel lines, except with a smaller diameter.

3 Concerning P0440 Symptoms

Error code P0440 will usually manifest in the following ways:

1. Active Check Engine Light

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

However, one thing to remember is that a lit engine light doesn’t provide specific information on the engine problem, so you’ll need a scan tool to confirm an EVAP issue.

2. Fuel Smell Caused by a Fuel Vapor Leak

Damage to several components (gas cap, hoses, vent valve, etc.) can cause a vapor leak, which triggers the P0440 code and results in a fuel smell. Typical causes include wear from age or debris damaging the EVAP components. 

3. Reduced Fuel Economy

The fuel system burns gas vapors during combustion to provide better fuel economy. If these gases escape due to leaks, the fuel system can’t use them. 

This means the engine only burns liquid fuel when operating, which causes the fuel level to drain quickly. 

11 Primary P0440 Causes

DTC P0440 can result from issues tied to various parts of the EVAP system. Some possible triggers include:

1. Missing or loose gas cap (fuel cap)
2. Incorrect fuel cap
3. Foreign matter caught in the fuel cap or fuel filler neck
4. Fuel filler neck damage
5. Bad fuel vapor pressure sensor
6. Damaged purge valve (purge solenoid) or vent valve
7. EVAP canister leak
8. EVAP hose leak
9. Leaking gas tank
10. Failing leak detection pump (LDP) pump or switch
11. Faulty gaskets or seals 

Is the P0440 Code Serious, and Can You Still Drive with It?

Yes, a P0440 code is a serious issue as it indicates a vapor leak. 

This means your vehicle is releasing harmful, flammable vapors into the environment. Exposure to these vapors is dangerous and detrimental to the health of the driver and passengers. 

While you can technically drive your car with the P0440 error code, it’s not recommended. Issues associated with this error code typically don’t cause vehicle drivability problems immediately, but they will result in a failed emissions test.

NOTE: Depending on your state, failing an emissions test may result in a penalty or denial of vehicle registration renewal. 

Diagnosing P0440

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

That said, here are the steps a mechanic would take during the diagnosis to identify a  P0440 code-related problem: 

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 see under what conditions the code was triggered.

2. Inspect the fuel cap to ensure it isn’t loose or damaged. Fix the cap and clear the trouble code to see if it comes up again.

3. If it isn’t resolved, 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, hoses, seals, or gaskets.

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.

5. Use a scan tool to test if the fuel tank pressure sensor can detect pressure in the fuel tank.  

Possible Solutions for P0440

The P0440 error code may sometimes require a combination of one or more repair procedures, depending on which vehicle component is faulty. 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 problematic component:

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

Cost to Fix P0440 Problems

Repair costs for DTC P0440 vary widely based on the problem. They typically range between $20 and $2,500 (including labor). 

Here are some estimates to consider: 

• New gas cap: $10 to $100
• EVAP line replacement: $50 to $100 
• Vent valve replacement: $160 to $220
• EVAP purge valve replacement: $180 to $320+
• Fuel vapor pressure sensor replacement: $265 and $380
• EVAP canister replacement: $470 to $520
• Fuel tank replacement: $700 to $2,500