P0446: EVAP System Vent Control Circuit Malfunction

What is P0446?

The fault code P0446 means your vehicle’s evaporative emission control system or the vent valve in the EVAP system is malfunctioning. 

The EVAP system comprises several critical components, including the gas cap, charcoal canister, purge valve, and vent valve. These EVAP system components work together to prevent harmful gas vapor from escaping into the atmosphere. 

When you turn off the engine, the EVAP canister purge valve remains closed (or has no voltage), trapping the fuel vapor generated in the gas tank. 

As soon as the engine is turned back on, your engine control module sends a command to the EVAP vent control valve to release the gas vapor into the engine for combustion via the purge valve. A voltage is applied to the purge valve for it to open. This also opens the vent valve, allowing fresh air to enter the canister.

Your vehicle’s evaporative emission control system conducts regular tests to check for leaks in the purge valve or vent valve. If the EVAP system detects a leak, it triggers the DTC P0446. 

Note: The fault code P0446 is one of the most common trouble codes with the GMC Sierra and Chevy Silverado. On the other hand, the Toyota Camry hasn’t listed the code P0446 since the 2007 model.

Common symptoms

Here are some of the most prominent signs of fault code P0446: 

1. An Illuminated Check Engine Light 

If your engine control module detects a gas vapor leak within the EVAP vent valve or canister, it triggers the Service Engine Light or the Check Engine Light on your dashboard. 

Whether you’re facing any drivability issues or not, you should have your vehicle diagnosed for code P0446 as soon as you see the Check Engine Light illuminated. 

2. A Spike In Fuel Consumption 

A sudden increase in your vehicle’s fuel consumption could be due to a damaged charcoal canister or purge valve within the EVAP system. 

Since the engine uses the trapped gas vapor for combustion, a leak in the EVAP vent valve or canister results in your engine requiring more fuel. You’ll notice the Check Engine Light flashing on your dashboard in such a situation. 

3. A Strong Fuel Odor 

Your vehicle’s EVAP is designed to trap fuel vapor in the charcoal canister and later release it via the purge valve into the engine to be burned. 

However, if the carbon canister or purge valve is cracked or damaged, the fuel vapor leaks into your car. Inhaling this harmful gas vapor can be dangerous to your health, so you should get your vehicle diagnosed at the earliest.

Can I still drive?

Apart from the Check Engine Light or Service Engine Light flashing on your dashboard, the fault code P0446 may not pose any immediate drivability issues. 

However, since the EVAP system plays an integral role in your vehicle’s functioning, leaving the P0446 code undiagnosed could lead to severe engine performance issues.

P0446 causes

While the most common cause for fault code P0446 is a loose or damaged gas cap, there could be other components causing a fault in your vehicle’s vent control valve or more. 

Here are some of the other prominent causes of fault code P0446: 

• Damaged or cracked fuel tank filler neck
• A leaking EVAP vent solenoid 
• Faulty electrical connections
• Damaged or defective fuel tank or fuel tank sending unit gasket
• Cracked or damaged charcoal canister
• Faulty EVAP system pressure sensor or vacuum pressure sensor
• A malfunctioning engine control module

Diagnosis

Conducting a diagnostic test for the fault code P0446 requires specialized tools and technical know-how. 

Here are the diagnostic steps a skilled technician would follow:

• Your mechanic will first use a scan tool to verify if the engine control module has stored other fault codes besides P0446. For example, if the fault code P0446 is combined with error code P0441 or P0440, the issue could be due to a faulty vent solenoid or EVAP canister.
• Next, the technician will examine the engine’s fuel tank, fuel tank pressure sensor, and gas cap.
• They’ll also read and analyze the fuel trim data as part of the diagnostic process to check for an imbalance in the air-fuel mixture.
• After inspecting the fuel cap, your mechanic will check for issues with the EVAP vent control valve and vent hose. Depending on the car’s make and model, your mechanic may need to test the purge valve by applying battery voltage. 
• The mechanic will clear any blockage between the vent line and the fuel tank by blowing compressed air through it. 
• Finally, the technician will check the EVAP system for potential electrical problems.

Possible repairs for P0446 & Costs

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

• Vacuum pressure sensor
• Gas cap
• Fuel tank sending unit gasket
• Charcoal canister
• EVAP canister purge valve 
• Fuel tank filler neck
• Fuel tank pressure sensor
• EVAP system pressure sensor
• Fuel tank
• Engine control module 

Repair costs:

The typical diagnostic costs for fault code P0446 range from $75-$150. Accordingly, you may need to replace one or more of the EVAP system components to fix the issue.

Here are the average estimated costs for some of the replacement parts (including labor charges): 

• Gas cap: $30 to $60
• Purge control valve or sensor: $150 to $200
• Fuel tank pressure sensor: $250 to $300
• EVAP charcoal canister: $450 to $500
• Fuel tank: $1000 to $1500 (could cost more depending on car make and model)