Evaporative Emission System Vent Control Circuit

Evaporative Emission Control System Vent Control Circuit Malfunction

What does that mean?

Evap vent valve has only one purpose. It closes in order to seal the vent so the EVAP system can pressurize and ensure there are no leaks. Evap vent valve is usually supplied Batt. voltage with key on.

The ECM's driver controls the ground, and when grounded, activates the valve (closing it). If the ECM detects a short to ground, and open, or a short to battery voltage on the control circuit, P0446 will set. Code also may refer to ECM detecting that EVAP system is unable to achieve or maintain vacuum during test.


There will be no obvious symptoms to driver, other than Malfunction Indicator Lamp (MIL) illumination.


A code P0446 could mean one or more of the following has happened:

  • Faulty vent valve
  • Open, short or excessive resistance on Vent valve control circuit
  • Blockage of vent valve
  • Bad PCM

Possible Solutions

With a P0446 OBD-II trouble code, here are some things to try:

  • Replace Vent valve
  • Repair open, short, or resistance problem in control circuit
  • Repair open, or short, or resistance problem in power circuit
  • Replace PCM

Other EVAP DTCs: P0440 - P0441 - P0442 - P0443 - P0444 - P0445 - P0447 - P0448 - P0449 - P0452 - P0453 - P0455 - P0456

Related P0446 DTC Discussions

  • what is the most likely fix for this code?...
  • Failed an emission test and got these codes. Guy was asking $150+ for diagnostics alone. What is something I can do to fix the problem? Thanks.
  • P0446 code came up. I replaced the vent valve. Cleared the code. Have driven over a 1000 miles and the 4 monitors won't reset ? I followed the drive cycle recommendations. Any one with a similar problem or a recommendation?...
  • Hello, I'm looking for help with a p0446 code. I have tested both the vent control valve and the purge valve. Both are working. With a bidirectional scan tool I can iniciate the evap test. When I do, I can here the vent valve close but don't here the purge valve open. I have power at the purge valve...
  • I have a 2000 Chevy Silverado, I get a code of P0446 when my gas tank reads half or less, when its full I dont get this code why is that? Ive already changed the evap filter.

Need more help with a p0446 code?

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