Evaporative emission control system vent control circuit malfunction 

 

 

Trouble code P0446 indicates that the engine control unit has detected an issue with your vehicle’s evaporative emission control system (EVAP) vent valve. The EVAP system reduces air pollution by preventing fuel vapors from escaping the gas tank into the atmosphere. It traps vapors in a charcoal canister until the engine can burn them. 

 

The vent valve controls outside air flow in and out of the charcoal canister. In some cars, it's also called a canister close valve (CCV) or vent solenoid. 

 

The figure below shows the basic scheme of an EVAP system: 

 

 

To make sure the EVAP system works correctly and to detect leaks, the engine control unit (ECU) runs regular tests. During these tests, the ECU sends a command to the vent valve to close and seal everything and then monitors the valve and control circuit for problems. If the ECU finds an issue with the vent valve or its wiring, it may trigger the P0446 code.  

 

Diagnostic trouble code P0446 often appears with other EVAP-related codes ranging from P0442 to P0463. 

 

 

 

Trouble code P0446 isn't critical and won't affect your vehicle's performance right away. However, you shouldn't ignore it. If the vent valve gets stuck in the closed position, it will increase the pressure in the fuel tank, making it difficult to refuel. 

 

If the valve is stuck open, it will cause an EVAP leak and impact your vehicle's emissions. 

 

Luckily, fixing the vent valve is relatively straightforward and won't cost you a fortune. 

 

 

Yes, you can still drive with a P0446 fault code, but it's wise to address the issue soon. While a vent system malfunction won't cause immediate damage, ignoring it can lead to other issues. For example, a persistent check engine light may mask a new, more severe engine problem. 

 

In addition, if the vent valve gets stuck open, it can leak fuel vapor, which harms the environment and your health. Prolonged exposure to these vapors can cause headaches, breathing difficulties, intoxication, and other respiratory problems. 

Symptoms of P0446

Common causes of P0446

How to troubleshoot P0446 

P0443: Indicates an electrical issue with the purge control valve circuit   

P0450-P0454: These codes specifically relate to the EVAP pressure sensor. Issues with this sensor can affect leak detection and overall system performance.  

P0457: Indicates that the gas cap is loose or damaged 

 

 

 

Use your scan tool to clear the fault codes.  

 

 

Then, drive your car for about 15 minutes to fully warm up the engine. 

 

After the drive, perform another scan to see if the issue reappears. If it does, it's an ongoing failure that requires further investigation to fix.    

 

 

Even though this isn't the main cause of the P0446 code, it's still quite common and worth inspecting since it only takes a few seconds. Make sure the gas cap is tight and undamaged.  

 

Check the condition of the rubber O-ring and replace it if necessary. If you notice any dirt or debris on the gas cap or seal, clean it using WD-40. 

 

Use a smoke machine  

 

Check the EVAP system for leaks. A smoke test is an effective way to locate leaks by filling the system with smoke. The smoke visibly escapes from any cracks, holes, or loose connections, so it's easier to identify the issue's exact location.  

 

 

If you don’t find any leaks, focus on the vent valve. Make sure the vent solenoid moves freely and isn't stuck, and clear any debris that might be blocking it. Also, look for a blocked EVAP vent path, pinched vent hose, or damaged EVAP vent housing.  

 

Finally, closely check the electrical circuit – inspect the wiring for signs of damage or loose connections. 

 

 

 

The EVAP vent valve is typically located near the fuel tank and is often attached to the charcoal canister, a large black box. Look for the EVAP canister under the car or, in some models, behind the rear wheel well. Refer to your vehicle’s service manual for the exact location. 

 

 

The cost of an EVAP vent valve typically ranges from $20 to a few hundred dollars, depending on the vehicle. The labor cost can add another $50 or more, based on the shop and location. The total cost will vary based on your car and where you get the repair done. 

 

 

If you ignore the P0446 code, you might fail a vehicle inspection and get fined.