Fault code P0440 – a step-by-step guide to diagnosing and fixing it

Error code P0440 is displayed and the check engine light is on - what does this mean?

The DTC P0440 indicates that the OBD system has detected a problem in the fuel vapor recovery system (EVAP). This fault code indicates a general malfunction in the EVAP system that prevents fuel vapors from being properly recovered. Different manufacturers may have slightly different names for this code, but it always refers to the evaporative emission system.

What can cause this error code?

• Defective or clogged activated charcoal container
• Damaged fuel filler cap or faulty fuel filler cap seal
• Cracked or porous fuel lines in the EVAP system
• Defective purge valve (purge valve)
• Faulty tank vent valve
• Blocked or damaged vapor lines
• Loose or corroded plug connections
• Defective pressure sensor in the fuel tank
• Leaks in the entire EVAP system

What symptoms occur in parallel with fault code P0440?

• Fuel smell: Perceptible smell of gasoline, especially when refueling or parking
• Engine performance: Slight loss of power or irregular engine running possible
• Fuel tank problems: Difficulty refueling or premature shutdown of the fuel nozzle
• Starting behavior: Occasionally difficult cold starts
• Fuel consumption: Minimal increase in consumption due to inefficient vapor recovery

How can the problem with error code P0440 be rectified?

• Repairing the EVAP system requires a systematic diagnosis, as various components can be affected.
• Check and replace the tank cap: Check the fuel filler cap gasket for cracks or wear and replace the entire cap if damaged, as this is the most common and cost-effective solution.
• Test EVAP lines for leaks: Perform a pressure test of the entire EVAP system, locate leaks with smoke test or soapy water and replace damaged lines completely.
• Replace activated charcoal container: Remove the carbon canister, check for clogging or damage and install a new canister including all connecting lines.
• Replace purge valve: Test the purge valve electrically and mechanically and replace it together with the associated vacuum lines if it is not working properly.
• Repair tank purge valve: Locate the vent valve on the fuel tank, check its function and replace it if defective, including the seals.
• Carry out a complete system diagnosis: Have a professional EVAP system diagnosis carried out using special tools and replace all faulty components in one operation.