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P0446: Evaporative Emission Control System Vent Control Circuit

Trouble code P0446 typically turns up in On-Board Diagnostic testing on account of an illuminated Check Engine Malfunction Indicator Lamp. This generic OBD-II code indicates that the evaporative vent valve in the emission control system is malfunctioning. When this occurs, the EVAP system may not be capable of pressurizing and maintaining a vacuum seal. Find out more about the most likely OBD-II scanner error code P0446 problem and related repairs.

What Does the Code P0446 Mean?

When a diagnostic scan of an automotive computer outputs the trouble code P0446, it is important to understand the meaning of the letter and numbers in this alphanumeric string. The letter P indicates a generic powertrain code, while the number 0446 points more specifically toward a malfunctioning vent control circuit in the evaporative emission control system.

Which Faulty Parts or Malfunctions Can Cause Trouble Code P0446?

P0446 tends to be returned by diagnostic testing when the control circuit for the evap vent valve is not achieving the seal that enables the EVAP system in the vehicle to hold pressure. The evap vent valve in most makes and models depends on a supply of a 12V battery voltage with key on. The ECM driver closes this valve when grounded and will set code P0446 if there is an open or short to ground or battery voltage or it is not possible to form a vacuum seal.

How Do I Fix Trouble Code P0446?

Resolving the problem causing this code can be a challenge because there are few indications of the problem beyond the vent valve itself. Check the specifications in the manual for your vehicle make, year model and engine build before attempting to test or repair vent valve control or power circuits, the vent valve or a faulty powertrain control module.

Some fixes may not require replacement parts. It can be a good idea to confirm that power is flowing through the control and power circuits and ensure that open, shorting or resistance problems are not present. Otherwise, it may be necessary to replace the evap vent valve or PCM to clear this code and turn off the Check Engine malfunction indicator lamp. If you fix the evap vent valve and resolve the problem, the Check Engine malfunction indicator lamp on the dash should turn off. If it does not and code P0446 is still set, problems with circuitry or parts persist. It may be necessary to replace other components to clear all trouble codes and make it possible for a vehicle to pass inspections.

Where Can I Run Follow-Up Diagnostics?

Running an additional diagnostic after the first round of repairs can help vehicle owners ensure that the problem is solved. Most dealers and mechanics have OBD-II scanners on site, but you can always rely on the free Fix Finder, which is available at AutoZone store locations, to determine which diagnostic codes could be causing a Check Engine light. If you don’t take all of the measures necessary to ensure that trouble code P0446 is cleared, this code could cause a vehicle to fail inspections or result in more serious engine or exhaust issues down the road.

Prior to an OBD-II diagnostic scan that identifies trouble code P0446, no indications of a problem may be present in vehicle performance other than an illuminated Check Engine light. There is not a single correct answer to the question, “how do I fix trouble code P0446?” It may be necessary to check the condition of circuitry and components and possibly even repair or replace parts such as the vent valve or PCM to clear this code and turn off the check engine light in a car or truck.

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