#OBD Codes
P0446 – Evaporative emission control system vent control circuit malfunction
Technical definition
Evaporative emission control system vent control circuit malfunction
What does P0446 mean?
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:
The basic scheme of self-testing 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.
How serious is P0446?
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.
Can I still drive with P0446?
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
If your car has a P0446 code, you are unlikely to notice any changes in performance, but some symptoms might show up. Besides the check engine light, a stuck closed vent valve often reveals itself when you’re filling up – the pump nozzle keeps shutting off, even with space in the tank.
If the valve is stuck open, you might notice a fuel smell near the tank and a slight increase in fuel consumption.
Common causes of P0446
Most often, P0446 appears due to:
- A malfunctioning or clogged vent valve
- Issues with the control circuit, such as loose or damaged wiring
Some vehicles rely on vacuum pressure readings in the EVAP system to evaluate vent valve operation. As a result, there could be more components that can trigger this code, including:
- A failed charcoal canister
- A malfunctioning purge valve
- A clogged or punctured vent hose or vent filter
- A failing EVAP system pressure sensor
- Cracked vacuum hose
How to troubleshoot P0446
Use these tips to diagnose and fix a P0446 code accurately:
Scan for other codes
Use an OBD scan tool to check for other related trouble codes, which may provide additional clues to the underlying problem. These include:
P0442, P0455, and P0456: Indicate leaks in EVAP system
P0441: Points to problems with the purge flow
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
Clear the codes and test drive
Use your scan tool to clear the fault codes.
Note: If the fault codes persist, this confirms that the problem is ongoing, so skip the following test drive steps and try other troubleshooting methods.
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.
Check the gas cap and seals
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.
Examine vent valve
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.
FAQ
Where is the EVAP vent valve located?
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.
How much does it cost to replace the EVAP vent control valve?
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.
What are the risks of ignoring the P0446 code for a long period?
If you ignore the P0446 code, you might fail a vehicle inspection and get fined.
Disclaimer: Advice, how-to guides, and car care tips on our blog are intended as helpful resources for general maintenance and repairs. While we strive for accuracy, the information is provided to the best of our knowledge and should be used at your own discretion and risk.
Always refer to your vehicle's owner's manual or consult a certified mechanic for specific repair details and safety procedures.
Always refer to your vehicle's owner's manual or consult a certified mechanic for specific repair details and safety procedures.