My 2004 Tahoe threw a P0442 code

Discussion in 'Engine & Drivetrain' started by ueww40, Aug 11, 2019.

  1. ueww40

    ueww40 TYF Newbie

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    My 2004 Tahoe threw a P0442 code the other day. 5.3 ltr flex engine. I understand it is a small leak somewhere in the evap system. I visually inspected all the lines to see if I could find something broken, but they all seem to be in order. I don't think it is the gas cap. The cap and seals look good and it feels right when I turn it the way it always has and should. How do you check the vapor canister vent valve and the vapor canister purge valve for proper operation? Should they be open or closed in home position? I inspected the vent valve to see if it was plugged up with dust or dirt, but it was not. Any ideas from experience what it could be? All suggestions are welcomed and appreciated.
     
  2. Scottydoggs

    Scottydoggs Full Access Member

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    smoke test will help a ton.

    the evap line does go all the way up to the engine, so look for a broken line up there as well.
     
  3. Big Mama

    Big Mama Full Access Member

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    Just chased this on my 07. I started with the cheap fix a new gas cap. My problem was vent valve solenoid on top of engine. A decent scanner or a tech2 can really narrow it.
     
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  4. ueww40

    ueww40 TYF Newbie

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    This problem has not been resolved yet. I was just away for a while. Here is what i did so far. I had my son, who vapes, blow a lot of smoke thru the AVAP service port right next to the Vapor Canister PURGE valve (the one with the green cap on and the left threaded Schraeder valve in it (for crying out loud why is the thing left threaded. I almost busted the whole thing trying to get it out until I figured out that it was a lefty.)), but that did not show any leaks. I figured, he may not be blowing hard enough so I actually went and ordered a smoke making machine, which worked like a charm, but there were NO leaks to be found anywhere. The only place where smoke came out was at the end of the line at the Vapor Canister VENT valve. I understand that the PURGE valve is normally closed (engine not running) and the VENT valve is normally open (engine not running). Can anybody explain to me what the function is of these 2 valves and how they are supposed to be doing whatever it is they are supposed to be doing while driving. Is there anything else that could cause a code P0442?
     
    Last edited: Sep 16, 2019
  5. ueww40

    ueww40 TYF Newbie

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    I thought the valve on top of the engine was the PURGE valve and the VENT valve is under the car. Please correct me if i am wrong.
     
  6. swathdiver

    swathdiver Full Access Member

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    This can be hard to trace. A bi-directional scan tool can put vacuum in the system and test the vent and purge valves to eliminate them. I've done this with mine and they passed. There are also lines above the fuel tank that can leak as can the Fuel Tank Pressure Sensor. The last time mine threw the P0442, it threw one for this sensor too. I cleared them and kept driving. Gas cap being a little over two years old with my children and wife fueling the truck, I just now put a new ACDelco cap on for $16 as I don't want to spend the money on a smoke machine yet. The code shows up usually every 16 or 18 ignition cycles but we're now at 21 or so and haven't seen it yet.

    This code usually throws during over night when the computer runs the tests.

    It's a colossal waste of time, money and resources to make the do-gooders feel good. Someday I'll throw all this stuff in the garbage and turn off or delete all that stuff from the ECM.
     
  7. Rocket Man

    Rocket Man Build It Better

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    If a new fuel cap doesn’t fix it I just replace both valves and if that doesn’t fix it I replace the charcoal canister. None of the parts are very expensive.
     
  8. swathdiver

    swathdiver Full Access Member

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    There's a hose underneath over the tank that's $130, so it could all exceed $500 if one shotguns it. The Tech-2 eliminated the purge and vent so it's between the tank and gas cap or something like that.
     
  9. Doubeleive

    Doubeleive Supporting Member

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    I would just do what Mark said shotgun it with the 3 parts and 99.9% of the time that resolves the problem, without a tech2 and the EXACT right conditions you probably won't find the one particular cause, doing the test with the tech2 is possible but boy it's tricky, you have to hit the buttons at just the right time, maintain a certain rpm, temp has to be right, ugh.
     
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  10. Rocket Man

    Rocket Man Build It Better

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    Vent valve is $13, purge valve is $20, canister is $80, all AC Delco. The hoses are unlikely to suddenly start leaking imo. Start with the cheapest of the 3 or do both valves to start.

    Edit: I didn’t see where he eliminated the purge or vent with a Tech 2?
     

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