P0446: EVAP Vent Control Circuit Malfunction

What Is Code P0446?

P0446, defined as EVAP Vent Control Circuit Malfunction, indicates an issue with the vent valve (also called the vent solenoid) or its control circuit in the EVAP system.

The evaporative emission control (EVAP) system in your vehicle prevents fuel vapors from escaping into the atmosphere by trapping them in a charcoal canister. 

How?
Fuel vapors from the gas tank flow into the charcoal canister, where they remain until the engine warms up from operation. As the engine temperature rises, the engine control module (ECM) opens the purge solenoid, allowing the stored vapors to flow from the canister into the engine for combustion.

Meanwhile, the vent valve remains open to allow fresh air into the canister, regardless of whether the engine is running. It only closes when the EVAP system conducts a leak test. 

If the vent valve gets stuck or fails, the system can’t perform the test properly, triggering a P0446 error code for a malfunction in the vent control circuit.

NOTE: Car manufacturers may interpret fault code P0446 slightly differently. For example, in Mercedes cars, the trouble code P0446 typically refers to “Activated Charcoal Canister Shut-off Valve”. In the GMC Sierra, Toyota Camry, and Chevy Silverado, it indicates an “EVAP Vent Valve Control Circuit Condition.”

What are the Common Causes of P0446 Code?

Although problems with various EVAP system components can trigger a P0446 error code, it typically points to an issue with the EVAP vent valve. However, pinpointing the exact cause requires professional diagnosis.

Some common reasons why this trouble code shows up include:

• Malfunctioning EVAP vent solenoid 
• Blocked EVAP vent valve due to debris  
• Faulty or loose connections in the EVAP vent solenoid
• Damaged or cracked fuel tank filler neck
• Missing or damaged gas cap
• Leaks in EVAP lines
• Damaged or defective gas tank sending unit gasket
• Cracked or damaged charcoal canister
• Faulty EVAP system pressure sensor or vacuum pressure sensor
• Malfunctioning engine control module

3 Telltale Symptoms of Code P0446

The most prominent signs of fault code P0446 are:

1. An Illuminated Check Engine Light 

If your vehicle detects gas vapor leaks within the EVAP vent control valve or canister, it triggers the Check Engine Light on your dashboard. 

However, the Check Engine Light doesn’t point to any specific information about the problem. So you’ll need to contact a mechanic to diagnose error code P0446 with a scan tool. 

2. A Spike in Fuel Consumption 

A sudden increase in your vehicle’s fuel consumption could be due to EVAP canister, vent solenoid,  or purge solenoid damage. 

Since the engine uses the trapped gas vapor for combustion, leaks in these components can cause your engine to require more fuel.

3. A Strong Fuel Odor 

The EVAP system traps fuel vapor in the charcoal canister and later releases it via the purge valve into the engine to burn. 

However, if the carbon canister has cracks or if the vent valve is stuck closed, pressure can build, resulting in fuel vapor leaks — usually near the fuel tank area. In rare cases, you might notice a strong fuel smell inside the vehicle.

Remember, inhaling this harmful gas vapor is dangerous, so you should get your vehicle diagnosed ASAP.

Can You Still Drive with Code P0446?

If your dashboard flashes the Check Engine Light, pull over immediately, as driving can severely damage your vehicle. In other cases, the error code P0446 may not pose any immediate drivability issues. 

However, the EVAP system plays an integral role in how your vehicle functions, so an undiagnosed P0446 code could lead to serious issues like engine misfires. Also, driving with a gas vapor leak in your cabin can cause various health issues.

How to Diagnose Code P0446

Conducting a diagnostic test for this EVAP system malfunction requires specialized tools and technical know-how. So it’s best to let a mechanic do it.

Here are the diagnostic steps a skilled mechanic would follow:

1. They’ll first use a scan tool like an OBD II scanner to verify if the ECM has stored other codes related to an EVAP system malfunction. For example, a P0440  may indicate a faulty vent solenoid, while a P0442 means an EVAP leak.

2. Next, they’ll examine the fuel tank, fuel tank pressure sensor (or EVAP vacuum pressure sensor), canister, and gas cap. Your mechanic will also read and analyze the fuel trim data as part of the diagnostic process to check for an imbalance in the air-fuel mixture.

3. After inspecting the fuel cap, they’ll check for issues with the EVAP vent control valve and EVAP hose. Depending on the car’s make and model, your mechanic may need to test the purge valve by applying battery voltage.

4. They’ll blow compressed air through the EVAP lines connecting the vent solenoid and the fuel tank or gas tank. This will clear any blockage from accumulated dust or other debris.

5. Then, they’ll pinch off the vent tube to the EVAP system to perform a smoke leak test. If they detect an EVAP leak, they’ll repair it.

6. Finally, they’ll check the EVAP system for potential electrical problems, such as loose or faulty electrical connectors.

Possible Repairs & Costs for P0446 Code

Depending on the diagnostic results of the P0446 code, here are some of the EVAP system components you may need to replace: 

• Fuel tank pressure sensor: $265 to $380
• Fuel cap or gas cap: $10 to $100
• Fuel tank sending unit gasket: $250 and $800
• Charcoal canister: $501 and $586
• EVAP canister purge valve or sensor: $150 to $200
• Fuel tank filler neck: $700 and $2,500
• Fuel tank or gas tank: $700 to $2,500
• Engine control module: $800 to $1,500