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P0440: Evaporative Emission Control System Malfunction

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What is P0440?

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

It’s an OBD-II generic code that indicates that the Engine Control Module (ECM) has detected a small leak in the fuel tank vapor system or that a fuel vapor pressure sensor has malfunctioned.

The Evaporative Emission Control (EVAP) System is responsible for safely discarding the fuel vapor residues outside the engine. 

When the vent valve is open, fuel vapors from the fuel tank (gas tank) travel through a vent fuel line to a charcoal canister (also known as the carbon canister or vapor canister). The fuel vapors are then absorbed and stored by activated charcoal pellets in the vapor canister. 

The purge volume valve controls how much fuel vapor is allowed into the engine. When opened, the intake vacuum from the engine draws the fuel vapors out of the charcoal canister and into the engine intake manifold. Here, it is used as part of the air-fuel mixture needed for combustion within the cylinders of the engine. 

So when the ECM detects inconsistencies in the EVAP control system, it pulls up code P0440 and triggers the Check Engine Light.

Common symptoms

One of the primary symptoms of the P0440 code is an illuminated Check Engine Light. However, the code P0440 can also 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. 

Since the Evaporative Emission Control system uses a fuel tank pressure sensor to identify a small leak within the exhaust system, it immediately triggers the Check Engine Light when something’s wrong. However, you need to look for other signs apart from the Engine Light to pinpoint the exact error code.

2. Fuel Smell Caused By The Leaked Fuel Vapor

The ECM triggers code P0440 when there’s a small leak within the EVAP system or if the EVAP system’s fuel tank pressure sensor is malfunctioning. 

In both scenarios, you might not be able to locate the leak physically. However, you may smell fuel vapor or a gasoline-like smell coming from the engine. You may also notice reduced gas mileage. This indicates potential problems with the fuel vapor system. 

3. Failed Emissions Test Or Smoke Test

Once you smell the fuel vapor, it’s best to get an emissions test or smoke test done. 

Your mechanic may pressurize the EVAP system with an EVAP smoke machine leak checker to check for smoke leaking out from any hoses or seals. If it does, you have a malfunctioning unit in the exhaust system.

Can I still drive?

Code P0440 and its severity can vary depending on the symptoms it exhibits. In most cases, the P0440 code will turn on the Check Engine Light, resulting in a failed emissions test. 

However, you may sometimes suffer from a vacuum leak in the EVAP hose or canister. This can be pretty serious and requires immediate attention.

P0440 causes

DTC P0440 can be caused by various issues pertaining to the EVAP system. That being said, the code does have some common triggers. 

These may include: 

  • Missing or loose fuel cap
  • Incorrect fuel filler cap being used
  • Fuel filler cap left open or unable to close
  • Faulty fuel filler neck
  • Foreign matter caught in the fuel filler cap or fuel filler neck
  • EVAP canister purge solenoid or fuel tank leaks
  • EVAP system hose leak
  • Leaking fuel tank or gas tank, loose gas cap, etc.

Diagnosis

Here are the 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. Next, 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. If not, perform an EVAP system leak check. Pressurize the EVAP system with an EVAP smoke machine leak checker and check to see if smoke leaks out from any hoses or seals.
  4. Next, inspect the purge valve. Start the engine and use a vacuum gauge. If there is vacuum coming out of the hose, then the purge valve is leaking and needs to be replaced.
  5. If the purge valve passes the test, check the EVAP vent valve for proper operation.

Possible repairs for P0440 & Costs

Trouble code P0440 may sometimes require a combination of one or more repairs. This is why it’s important to fully diagnose the issue before replacing car parts. 

Here what your mechanic may do:

  • Tighten the gas cap 
  • Replace or repair sealing in the gas cap
  • Replace the fuel tank (gas tank)
  • Replace the EVAP purge control valve
  • Fix wirings to the EVAP purge control valve
  • Replace damaged or disconnected hoses around the EVAP purge solenoid
  • Replace damaged EVAP pipe, fuel line, or vapor lines
  • Replace charcoal canister (rare)

Repair costs:

DTC P0440 is a relatively inexpensive code to resolve. It typically costs anywhere between $90-$350, including labor charges and the cost of parts

Here’s a closer estimate of the various repair solutions for P0440: 

  • Gas Cap: $20 – $60
  • EVAP Line: $20 – $100
  • EVAP Vent Valve or Canister Vent Solenoid: $150 – $200
  • Purge Volume Control Valve: $150 – $200

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