P0446 CODE: Evaporative (EVAP) Emission Control System Vent Control Circuit

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P0446 code is set off when the computer of your vehicle's engine detects a restriction or a problem at the vent control portion of the Evaporative (EVAP) Emission Control System.

The exact description of the issue differs from one car model to the other, so you'll need to do some testing to pinpoint the defective component. Continue reading to find out more about the code P0446.


P0446 Code Definition

P0446 is a diagnostic trouble code (DTC) which is a generic OBD2 powertrain code. It applies to all vehicles manufactured since 1996, but some models will require additional or specific steps for repairing.


What Does the code P0446 Mean?

The code P0446 is triggered by the engine computer (ECU) when there's a malfunction in the EVAP control system vent control valve.

How does the EVAP system vent control work?

The Evaporative (EVAP) Emission Control System is one of the methods your engine uses to limit its harmful emissions. It prevents the escape of fuel vapors from the fuel tank to the atmosphere.

These vapors are trapped in the charcoal canister where they get absorbed into small pellets made of activated charcoal.

There are 2 main valves contributing to the flow of air in and out of the system:

  • The vent control valve – this electrical valve is controlled via the engine control module (ECM) and it regulated air supply into the charcoal canister. It's usually installed at the rear of the vehicle close to or at the charcoal canister.
  • The purge volume control valve - this valve allows vapors to travel from the EVAP system into the engine air intake to be burned.

Normally when the engine is running, the vent control valve is open while the purge volume control valve is closed. When the ECM is ready to expel the fuel vapors, it opens the purge valve to burn the stored vapors from the charcoal canister.

The ECM performs occasional leak tests to make sure that the EVAP emission control system is functioning properly when the vehicle is turned off.

During these tests, the ECM shuts off the EVAP system by closing both the vent control valve and the purge control valve to establish a sealed EVAP system. Then, the ECM monitors the pressure in the EVAP system.

The P0446 code is triggered if the EVAP system fails to maintain proper pressure during the leak test, or if the ECM detects a short in the vent control valve activation circuit.


What are the Causes of the Code P0446?

  • Detective vent control valve
  • The vent control valve is blocked
  • The vent filter or the vent hose are blocked
  • The fuel cap is missing
  • A mismatched fuel cap is being used
  • Something is caught up the fuel filter cap
  • Faulty charcoal canister
  • Damaged fuel tank filler neck
  • Open or shorted vent control valve circuit
  • A leak in the EVAP system

Other Troubleshooting Codes about Evaporative EVAP Emission Pressure Sensor

P0452 CODE: Evaporative (EVAP) Emission Pressure Sensor Low Input

P0453 CODE: Evaporative (EVAP) Emission Pressure Sensor High Input

Other Troubleshooting Codes about Evaporative EVAP Emission System Leak

P0455 CODE: Evaporative (EVAP) Emission System Large Leak

P0456 CODE: Evaporative (EVAP) Emission System Small Leak

Another Troubleshooting Code about Evaporative EVAP

P0496 CODE: Evaporative (EVAP) Flow During a Non-Purge Condition


What are the Symptoms of the P0446 Code?

The problems caused by the P0446 code don't really manifest themselves in drivability issues. However, there are a couple of symptoms that you can notice:


Is the Code P0446 a Serious Problem?

The P0466 code ranks low on the seriousness scale. The driver probably wouldn't notice any change associated with the P0446 code except for the check engine light going off.

That being said, it's important that you fix the problem as soon as possible, just like any other check light engine DTC.

How to Diagnose the P0446 Code?

  • You can start by using a scanning tool to check if there are any diagnostic trouble codes present and observe any freeze frame data.
  • Clear all codes from the engine computer.
  • Visually inspect all the components of the EVAP system for any damage in the charcoal canister, the fuel tank, the fuel cap, as well as the EVAP hoses and lines.
  • Use a multimeter to check the vent control valve and the purge valve.
  • Use a scan tool to monitor the EVAP system pressure.
  • Use a smoke machine (set to visible vapor or smoke) to check if there's a leak in the EVAP system.

How to Repair the P0446 Code?

Here are a few ways to fix the code P0446

  • Replace the EVAP system hoses
  • Repair or Replace the fuel tank.
  • Replace the charcoal canister.
  • Use a proper or new gas cap.
  • Replace faulty vent valves.

About the Author JamesL Davis

James is a certified auto technician specializing in commercial vehicles. With 30 years of experience under his belt, James has encountered almost every type of automotive issue there is! Besides his day job at the repair shop, he is also an amateur race car driver.

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