P0446 OBD-II Trouble Code: Evaporative Emission Control System Vent Control Circuit Malfunction

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P0446 is a diagnostic trouble code (DTC) for "Evaporative Emission Control System Vent Control Circuit Malfunction". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

Cars Estimate Credit towards follow-up repair Earliest Availability
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Toyota$20.00
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P0446 code definition

P0446 is an OBD2 diagnostic trouble code that indicates a fault within the evaporative emission control system. Other EVAP system codes may be seen with P0446.

What the P0446 code means

The P0446 code is triggered by the ECU when a malfunction occurs with the EVAP control system vent control valve. The ECU controls this valve as part of the EVAP control system and when the a fault is detected a Check Engine Light appears on the dashboard

What causes the P0446 code?

  • Faulty, missing, or broken gas cap
  • Faulty EVAP system hose
  • A Leaking fuel tank
  • Broken or faulty charcoal canister

What are the symptoms of the P0446 code?

  • The Check Engine Light being present.
  • A fuel odor may be noticed and the fuel economy may suffer slightly.

How does a mechanic diagnose the P0446 code?

  • Uses the scan tool to check for any codes present and notes any freeze frame data

  • Clears all codes from the vehicle's computer

  • Performs a road test of the vehicle to confirm the complaint

  • Performs a visual inspection on all of the EVAP system's components looking for damage to the gas cap, fuel tank, EVAP lines, and charcoal canister

  • Inspects the gas cap for any damage and insures proper fitment with a gas cap tester

  • Uses a scan tool to monitor tank pressure data and make sure it is reading properly

  • Performs a self test of the EVAP system with a scan tool to check the functions of all the valves and solenoids

  • Performs a test a smoke test of the EVAP system if no conclusive answers arise from any of the previous test

Common mistakes when diagnosing the P0446 code

Mistakes can commonly occur with the P0446 code when care is not taken to follow all steps without skipping any. P0446 can caused by many different components so care must be taken to test all of these properly to avoid misdiagnosis.

How serious is the P0446 code?

The driver generally will not notice any of the symptoms from P0446 other than the check engine light. P0446 will not stop the vehicle from driving properly but like any check engine light should be repaired ASAP for normal operation of the vehicle.

What repairs can fix the P0446 code?

  • Repairing or replacing the fuel tank as needed
  • Replacing the gas cap
  • Replacing the charcoal canister
  • Replacing the EVAP lines

Additional comments for consideration regarding the P0446 code

Without the proper tools EVAP system codes such as P0446 can be very difficult to pinpoint. When leaks are suspected the technicians will use a smoke test machine on the EVAP system. The smoke test will show any leaks that may not have been visible before as the leaks are generally much smaller than the human eye can see.

An advanced scan tool is another tool used in the diagnosis of the P0446 code. These scan tools do much more than just check for codes and clear them. They allow live ECU data to be viewed and changes over time to be visible.

In addition for EVAP system codes a high end scan tool will enable the car’s EVAP self test to be performed. These tests are done to command the vent and purge solenoid to turn on and off as well as test the system to point at what part of the system the malfunction or leak is coming from.

Need help with a P0446 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

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