Diagnostic Trouble Code P0446

P0446 “Evaporative Emission Control System Vent Control Circuit Malfunction”


What is code P0446?

Code P0446 stands for “Evaporative Emission Control System Vent Control Circuit Malfunction”. This diagnostic trouble code can show up for a number of problems related to a leak in the evaporative emissions (EVAP) system. Therefore, it is important to have a qualified technician diagnose the specific problem that caused the code to be stored in your vehicle’s computer.

Get this checked out soon by a CarAdvise shop, where the work will be guaranteed, and one of our expert techs will review any repair orders.

What does code P0446 mean?

When code P0446 shows up on a diagnostic scan of your vehicle, a technician knows that there is something going wrong with your EVAP system.

Gasoline has a tendency to evaporate, especially when it is warm outside, or when you are filling the gas tank at the pump. This evaporation not only depletes your store of fuel, but also allows harmful pollutants to enter the atmosphere. For this reason, vehicles are fitted with an evaporative emissions control system, also known as the EVAP system. This collection of tubes, sensors, and valves connected to the fuel tank allow evaporating vapors to be collected in a special receptacle, the EVAP canister, where they can be reintroduced into the fuel system to be burned by the engine at a later time.

Although different manufacturers have various designs for their EVAP systems, generally at some point while an engine is running, the ECM (Engine Control Module) that oversees the function of your engine and other systems will command the EVAP system to be purged. When this occurs, the purge valve opens and the vent valve closes. This allows stored fuel vapors to be drawn out of the EVAP canister so that they can be burned during combustion.

If there is an error in the vent valve circuit, the valve may fail to close, and the vapor canister would not be evacuated. The EVAP system might also fail to hold a vacuum properly. The ECM is likely to detect an improper return voltage from the vent valve. It will store code P0446 and turn on the check engine light.

What causes code P0446?

A number of causes can trigger a code P0446. That is why an accurate diagnosis is essential. Causes of this code relate to any component in the EVAP system that could facilitate a leak. For instance:

Most likely

Other possibilities

  • Bad ECM

What symptoms are associated with this code?

Common signs associated with a code P0446 include the following:

  • The check engine light is on
  • Reduced fuel economy
  • Failed emissions test
  • Smell of fuel outside the vehicle

How does a technician diagnose code P0446?

If a diagnostic scan of your vehicle indicates a code P0446, a technician will perform tests to pinpoint the problem. These tests include checking for any related trouble codes. The technician will also use the scan tool to command EVAP components to function, such as opening and closing the vent valve, to observe certain characteristics that might indicate if the component is working. The technician will likely perform a visual inspection of the valve and related wiring, and use a multimeter to test the vent valve. If necessary, a “pinout test” of the valve’s wiring might be done to determine if an issue exists between the valve and the ECM.

How serious is this code?

A code P0446 is not likely to cause any immediate drivability issues. It will, however, prevent your vehicle from passing an emissions test. An EVAP system leak can get worse with time and could lead to additional diagnostic trouble codes. In some cases, a fuel vapor leak could even cause engine misfires. Code P0446 is not cause for immediate concern, but it should not be ignored long-term. Look to have your vehicle inspected within a week or so.

Get this checked out soon by a CarAdvise shop, where the work will be guaranteed, and one of our expert techs will review any repair orders.


Related Diagnostic Trouble Codes

P0440 “EVAP System Malfunction”

P0442 “EVAP System Pressure Sensor/Switch A Circuit”

P0456 “EVAP System Leak Detected (large leak)


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