All vehicles have an evaporative emission control (EVAP) system specifically designed to prevent releasing toxins into the air. When you put your gas cap back on, it traps the fuel and its toxins inside.
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Fuel vapors go through a vent line into a charcoal canister, where activated charcoal absorbs some of the fumes. The electronic control module (ECM) then allows the vent valve to push the fumes into the engine air intake.
Vapors travel to the engine air intake through the purge valve. Once there, they mix with air and fuel, creating the combustion that powers vehicles. If the vent control valve doesn’t work, it triggers the P0446 code.
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What Does Code P0446 Mean?
OBD-II Trouble Code P0446 DescriptionEvaporative Emission Control System Vent Control Circuit Malfunction
The vent control valve and the purge valve make the EVAP system work. The vent control valve keeps the system moving by pulling fumes in, then pushing them out through the purge valve.
The purge valve acts as the exit to the engine air intake. The only way fumes can get through the purge valve is if the ECM tells the vent control valve to let air through. The P0446 code appears when the vent control valve experiences a malfunction.
These issues appear during the ECM’s regular testing. When the vehicle isn’t running, it tests the EVAP system for leaks by closing the vent control valve. Closing the valve seals the EVAP system off completely, and no air or fumes should escape.
If the vent control valve cannot maintain enough pressure to seal the EVAP system, it triggers the P0446 code.
Symptoms of Code P0446
The P0446 code produces three primary symptoms. The first and most conspicuous symptom is a check engine light.
Second, look for a decrease in your vehicle’s fuel economy. If you find yourself heading to the gas station more frequently, you might want to get a diagnostics check-up.
Third, you may notice a gasoline odor. Since the vent control valve can’t seal itself, the fumes can escape and create a fuel smell around your vehicle. Inhaling these gas fumes can be dangerous to your health.
Causes of Code P0446
A broken, damaged, or improperly installed gas cap most commonly raises the P0446 code. However, other, less common causes can also arise. They include:
- Vent control valve: Without a working vent control valve, two things could happen. A faulty vent control valve can seal the fumes inside with nothing to move them, or the vent control valve can’t maintain enough pressure to keep seal the vapors in at all.
- Fuel tank filler neck: If the fuel tank filler neck has a crack, pressure can’t hold. The crack will undermine the pressure from the vent control valve. The fuel tank filler neck may also be distorted or damaged in another way to creat the same effect.
- EVAP system hoses: Pressure can also leak from the hoses in the EVAP system. A smoke test can diagnose this issue.
- Fuel sending unit gasket or seal: This gasket or seal ensures that the fuel stays in the unit and doesn’t drift elsewhere in the vehicle. Even if fuel doesn’t leak, the pressure may weaken.
- Charcoal canister: This can split or become damaged. As the main component that holds fumes, the charcoal canister crucial to the EVAP system.
- Fuel tank: The fuel tank can cause the P0446 code to display, as the fuel tank feeds the EVAP system.
- Electrical connections: Vehicles run on electrical connections, just like computer. A shorted or open electrical connection affects the EVAP system.
Is Code P0446 Serious?
The P0446 code won’t put you in any immediate danger. You can still drive your vehicle if you see this code. Other than the check engine light, you may experience reduced fuel economy.
While this code may not create life-threatening problems, anything that triggers a check engine light deserves attention.
How to Fix
To fix code P0446, you should first inspect the gas cap. EVAP system issues have many potential causes, making them more difficult to diagnose. Taking a progressive approach from least to most severe is most efficient.
If the gas cap is faulty, damaged, or deteriorating, replace it and then clear the code. If the P0446 code persists, check for a leak. Some mechanics use a smoke test to check for leaks. A smoke test pushes smoke through the EVAP system to see if the smoke exposes any leaks. After you repair the holes (if you find any), clear the code.
The next move is to check the EVAP controls. They could be sticky, clogged, or have an internal solenoid failure. There are several ways to check the controls. Try blowing through the vent control valve. If it doesn’t open, it may be sticky or clogged.
Replace any damaged parts, clean the pieces already there, and check for the P0446 code again.