The evaporative emission control system in your car helps to purify pollutants from the combustion process. This is important for keeping your car within your state’s emissions guidelines and helps your engine run efficiently.
The trouble code P0446 often tells you there’s a problem with the vent control that regulates airflow into and out of the system. This isn’t always the answer when you get this code, though, as you’ll see from the explanation below.
P0446 code definition
Evaporative Emission Control System Vent Control Circuit Malfunction
What does P0446 mean?
The EVAP (Evaporative Emission Control) system is part of your engine’s way to reduce its harmful emissions. It keeps fuel vapors from reaching the atmosphere by absorbing them into charcoal pellets.
Two key valves control when air can flow in and out of the system. The vent control valve lets air into the charcoal canister and is controlled by the engine control module. The purge valve controls the flow of vapors out of the EVAP system and into the engine air intake.
When the engine is at its operating temperature, both the vent control valve and the purge valve are open. However, the engine control module periodically tests the valves for leaks, closing them and creating a vacuum. Problems during these periodic tests trigger the code P0446.
What are the symptoms of the P0446 code?
The problems that cause the code P0446 don’t usually lead to any drivability issues. There are some detectable symptoms, which include:
- Activation of the check engine light
- Fuel odor while driving
- Reduction in fuel economy
What are the causes of P0446?
There are a few systems that could contribute to the P0446 trouble code, such as:
- Vent control valve: A faulty valve will trigger this trouble code. It could also be blocked or dirty, or there could be an issue with the circuit that controls it.
- EVAP system: The charcoal canister itself may be damaged. There could also be damage to the surrounding hoses and gaskets.
- Fuel tank: The tank itself could be leaking or damaged. The fuel cap could also be cracked, deficient, or missing.
- Powertrain control module (PCM): If the PCM is bad, it won’t control the vent control valve properly. The wires around the PCM could also be damaged or faulty.
How serious is the P0446 code?
The P0446 trouble code is not serious. You may not even notice any changes in how your car drives. At worst, you’ll have to fill your tank a bit more often than usual. Having said that, you should still repair the issue as soon as you can to keep your engine running correctly.
How to diagnose the P0446 code?
Tools you’ll need:
- Advanced OBD2 scanner
- Digital multimeter
- Smoke machine
- Scan your vehicle to check for other trouble codes. If you see P0440 or P0441 along with P0446, the issue may be more serious. Fix other codes first, then scan your vehicle again.
- Inspect your gas cap. Tighten it if it’s loose, and replace it if it’s cracked or damaged. Also, check the fuel tank for leaks or other damage.
- Check the hoses around the EVAP system for cracks or weaknesses. Replace any that are damaged and reconnect any hoses that have come loose.
- Check the tank pressure data using an OBD2 scan tool and make sure it’s reading correctly.
- Visually inspect the charcoal canister for leaks and other damage.
- Use the scan tool to check all the valves and solenoids of the EVAP system.
- Test the vent control valve and the purge valve. Use a multimeter to test that they’re receiving power. If they’re not, check the wiring.
- Use a smoke machine to test the EVAP system for leaks. With your engine off, use your scan tool or a multimeter to close the vent solenoid. Connect the hose of the smoke machine to the EVAP system and turn on the machine. Watch the indicator ball. If it goes above the red flag, there is a leak in the system; go on to step 9.
- Put the smoke machine on the “visible vapor” or “smoke” setting. Remove the fuel cap until you can see smoke coming out of the filler neck. The vapor in smoke machines is UV reactive, so shining a black light on your engine will help you see the location of leaks more quickly. Repair any leaking hoses you find and repeat step 8 until it passes.
Common mistakes to avoid while diagnosing the P0446 code
Misdiagnosis is the most common mistake. There are a lot of different components that could be the root cause of the P0446 trouble code. Check all the possible causes to make sure you don’t replace your charcoal canister when all you need is a new gas cap.
What should you do to fix the code P0446?
- Replace any leaking or damaged components found during your diagnostic testing.
- If the vent control valve or purge valve is receiving power but not opening and closing properly, the valves themselves are the likely culprit. Replace the sticking valve(s).
- Remove the charcoal canister. You can use compressed air to clean it. Place it on a flat surface and start the air compressor, letting the pressure build to 50 psi before shutting it off. Put the nozzle into the vent control valve pipe on top of the canister and cover the other two openings with your fingers. Allow the compressed air to blow into the canister for 1-2 minutes.
- Replace the charcoal canister and test the EVAP system. If it’s still failing, the charcoal canister may need to be replaced.
Tips to avoid P0446 in the future
Regular preventative maintenance of your EVAP system is the best way to avoid problems. This starts by making sure your gas cap is on tightly after every fill-up. Rust prevention treatments on your system can also prevent corrosion, which is the most common cause of system leaks.