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Code: P0304 head gasket?

Discussion in 'Gen 3 Prius Technical Discussion' started by HungryHungryHippo88, Jan 30, 2020.

  1. HungryHungryHippo88

    HungryHungryHippo88 New Member

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    Hey guys, took car to dealer after getting p0304 code at oreilly's and auto zone. Always good to make sure so i double checked.

    10 minutes after dropped off car at dealer.

    Engine light wasn't even on upon drop off.

    Came and went the last few times upon starting.

    Was getting rough idle and sputtering when lightly accelerating.

    Came and went for a little over a week.

    Took it in and awaiting word expecting new plugs were needed.

    Haven't put new plugs In yet.

    136,500 miles on it. Just had battery replaced under warranty a few weeks ago.

    Could this be a head gasket issue?
     
  2. Priuslover09

    Priuslover09 Member

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    No it’s cylinder code
     
  3. Priuslover09

    Priuslover09 Member

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  4. Grit

    Grit Senior Member

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    When were the plugs last changed? And miles when changed?
     
  5. tgotr

    tgotr Junior Member

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    No, a head gasket issue would result in the engine overheating after a short while and the oil looking milky due to coolant contaminating it.

    p0304 means Cylinder 4 is misfiring, which could be the ignition coil pack for that cylinder, or the plug
     
  6. Triparadox

    Triparadox Active Member

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    I'm pretty sure mine didn't go to overheating when the head gasket issue was a thing. Also, the milky looking coolant is hard to spot. My head gasket was fucked up on 2 cylinders, and I couldn't even see any milky stuff from coolant, or the engine oil / cap.

    Posted via the PriusChat mobile app.
     
  7. Mendel Leisk

    Mendel Leisk Senior Member

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    Yes it could be. Try a leak-down test.

    Have you cleaned the EGR circuit and intake manifold?
     
  8. Grit

    Grit Senior Member

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    Not replacing the plugs at its interval change may contribute to head gasket leak and not just limited to that.
     
  9. The Critic

    The Critic Resident Critic

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    ??
     
  10. Triparadox

    Triparadox Active Member

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    You mean spark plugs? Can you elaborate on how that affect the gasket? As far as I understand, head gasket issue is mainly caused because of overheating, or it simply just wear out specifically on Prius Gen III.

    Posted via the PriusChat mobile app.