Fault code P0446 – a step-by-step guide to diagnosing and fixing it

P0446 indicates that the evaporative emission control (EVAP) system vent valve is malfunctioning. The EVAP system works to prevent fuel vapours from escaping into the atmosphere. The vent valve allows fumes to enter into the system and flow to the charcoal canister, where they are absorbed and stored. The engine control module performs a leak test while the vehicle is switched off. To do so, it closes both of the EVAP valves to keep fumes sealed inside. If the module detects a short circuit when trying to activate the vent component, or the EVAP pressure is not maintained, it will trigger this code.

• A cracked or faulty fuel filler neck, or a broken fuel cap. This kind of damage leads to a loss of pressure as vapours will leak through the components.
• Punctured EVAP hoses. This can also be the cause of a leak.
• A short or open circuit in the vent control solenoid, a damaged connector, or corroded contacts. Corrosion can occur exposure to moisture, dirt and other substances, affecting the conductivity of wires and connectors. Thermal damage may also occur. These faults will impact the device’s power supply. If the valve is faulty, it may not be able to contain the vapours or let them pass through.
• A clogged vent tube. If the solenoid device won’t close properly the vent tube could get clogged. This can damage the canister.
• Broken gaskets or seals

• Activation of the check engine light
• A strong fuel smell
• Poor car engine components performance
• An increase in fuel consumption
• Incorrect fuel level readings

• You will need to identify the cause before proceeding with repairs. First, you may want to start with the fuel cap, as this is easy to inspect and repair. Replace the cap if there are signs of damage, and tighten it if it is loose.
• Check for leaks in the system. The most effective way to do this is using a smoke machine. This is normally how mechanics diagnose leaks or sealing problems, however, not everyone has access to this equipment. It may also be possible to detect the cause of the fault by reading and deciphering the DTC. Connect an OBD2 scanner to the vehicle via the data link connector port. Related ODD codes include P0456 and P0442. Leaks can often be fixed by installing new components, such as seals and hoses, or by repairing a damaged fuel tank or filler neck. This may involve the use of epoxy resins or a soldering repair method.
• Unblock tubes or hoses by removing contaminants with compressed air. Inspect the components for cracks, punctures and deformation, and replace if necessary.
• Restore the power supply and electrical connections by removing traces of corrosion and replacing damaged wires, etc. The electrical contacts can be cleaned and treated with a specialised product to improve their conductivity.
• If there are problems with the circuit of the vent valve or leaks, the best solution is to replace it.
• Once you have finished repairing the system, reset the DTCs and take the vehicle for a test drive.