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Thread: Code P446

  1. #1

    Default Code P446

    My 02 Sierra is showing a P446 trouble code, something to do with evaporative emissions? Help please?

  2. #2


    Welcome to the site.

    P0446 is a code that has to do with the evap vent/purge

    The evap vent valve closes in order to seal the vent so the EVAP system can pressurize and ensure there are no leaks. This valve is usually supplied battery 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. A loose, improperly sealing or missing gas cap will cause this error as well.

    There are no symptoms other than the warning light.
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  3. #3


    This code is a plague! My 05 SIERRA popped this code about 2 years ago. I replaced the vent valve assembly and 2 months later it came back! It didn't affect ant functions....except pop the stupid light. Year and a half go's bye and the light finally went codes either. Must have been stuck or something?!?!?!

  4. #4


    Thanks guys, truck runs fine just light on kinda annoying...

  5. #5


    Evap codes can be a monster to track down! One small pin hole in the wrong (or right) place can really create problems!

  6. #6


    One more thing, when I loosen the gas cap I get a whooshing sound, sucking in I think as i don't smell gas...

  7. #7


    Quote Originally Posted by jaygilman48 View Post
    One more thing, when I loosen the gas cap I get a whooshing sound, sucking in I think as i don't smell gas...
    Your vent is not venting!

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