Quick fix for code p0446 evap emissions vent circuit low.

Discussion in 'How-to Guides' started by kinglt1, Feb 17, 2009.

  1. ChevyFan

    ChevyFan The Sheriff Staff Member 5+ Years 1000 Posts

    Over 400,000 views on this thread, and growing. :)
  2. zods1984

    zods1984 New Member

    I have a 2004 Avalanche. My mechanic has changed the solenoid, purge valve and the charcoal canister. I even changed the gas cap. My mechanic and another shop was telling me that since all of the parts of code 0446 has been changed, the only thing that I can do now is take it to the dealership and have them reset the engine's computer. When I called the Chevy dealership, the service advisor said that they don't reset the engine's computer. I would have to take it in and they would do a diagnostic test for $150. I have looked at alot of forums regarding code 0446 and I haven't found an answer to this problem. Does anybody have a solution that I can try? Many thanks!!
  3. Macarchie

    Macarchie New Member

    I'm assuming from your post that the CEL is still on and that you don't have an ODBII scanner. Your mechanic should have cleared the code when the repair was made. If he didn't, the light should go off after you've driven the car for a while (probably after a couple of hours). Some auto parts stores will hook up a scanner, read the code and erase any codes if you ask them. If the components have been replaced and the light stays on, then there may be a kink in the air line where it bends or an air leak at one of the joints. I used a longer piece of 5/8" hose to keep the hose from collapsing around the bend and then used a wire tie to ensure it doesn't get too close to the driveshaft.
    Good Luck!
    - Jimmy
  4. zods1984

    zods1984 New Member

    Hi Jimmy, thank you for your suggestion. The mechanic did reset the code and it came back on after 150 miles. I took it to autozone and they reset the code for me and the CEL came back after 160 miles. I will take it back to the shop again. One of the mechanics had also mentioned something about flashing the computer? Thanks again.
  5. j cat

    j cat Epic Member 5+ Years 1000 Posts

    in the GM service manual on the 1996 B body full sized caprice/impala etc. the valve is subject to getting blocked causing the vent code. manual says to blow out the valve energizing the valve ... the other component to be checked is to remove the fuel cap and blow air back into the fuel tank from the canister , to be sure that line is clear.

    the other problem that many run into is the canister gets damaged from liquid fuel.this is quite common on these trucks because the canister is mounted close and low to the fuel tank.

    on the B body vehicles and other older GM vehicles the canister is mounted up front near the engine so this liquid fuel issue is much less ..
  6. Macarchie

    Macarchie New Member

    Sure sounds to me like what I went thru. After the initial fix, the CEL came on and I checked it. The hard plastic hose had collapsed where it bends back to connect to the tank. It was a real pain and finally I just replaced the hose with a longer 5/8" heater hose with radiator clamps on each end. That fixed it. On my '06 Sierra, the original hose was really hard to work with and trying to reuse it was a waste of time.
    I would climb underneath and take a real good look at the hose and connectors before paying to get the computer flashed. If you can get it up on a lift, it is much easier.
    Hope this helps.
    - Jimmy

  7. zods1984

    zods1984 New Member

    I will be taking it back to my mechanic again. He said he would recheck the hose for me. I will let you guys know if this works. Thanks for all of your suggestions!
  8. hanleyclifford

    hanleyclifford New Member

    Hi - I'm new to the forum, have a 2004 Silverado with 5.3 V8. After getting the P0446 code I read this thread and performed the operations suggested. I took the evaporator valve cannister assembly including hose out of the vehicle and cleaned it thoroughly. I also removed the rectangular cannister that sits forward of that unit and blew it out thoroughly, but the code came back. Can anyone suggest the next move? I'm stumped. Edit: I took the canister, valve and hose out again for another try today. Looking into the bottom of the valve I saw a spring which I was able to get out. There was also what appeared to be a rubber or leather which presumably is the "piston", or sealing unit inside the "cylinder". I did not attempt to remove that. Is it possible grit could have gotten into this area so that even if I blow the thing out again and again it will not function normally and will set the code? I erased and will now see if the light comes back on before the monitors show "ready".
    Last edited: Jun 15, 2014
    ChevyFan likes this.
  9. saloncuts

    saloncuts New Member

    I have a 2007 Chevy Trailblazer with the code P0446 popping up too. Not the gas cap, as it was not loose, and we tightened it & code came back. Now going to try the Vapor can Vent Valve (part #911-033) Does this usually fix the problem or does the charcoal canister need to be replaced too?
    Last edited: Aug 22, 2014
  10. Dukhunter

    Dukhunter New Member

    I have had a P0446 for a while now and can't seem to get the thing to go away. I have blown out the vent valve. Light came back on 2 weeks later. I then replaced the vent valve. The CEL came back 3 weeks later with the same code. I have now tried replacing the purge solenoid. I read a post on here that it could be the fuel tank pressure sensor causing a P00446. Is this correct? Any additional information would be much appreciated.

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