Engine Knocking P0304 Code

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Seth Holloway, Sep 8, 2021.

  1. Seth Holloway

    Seth Holloway Junior Member

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    I have a 2012 Prius with 127,000 miles on it. I was running a few short errands today and the engine started knocking. I made it home and started watching some videos on youtube and then put startedd searching and found the Carista OBD2 that I bought a few years ago. Plugged it in and ran the test and came back with Code P0304 4Cylinder misfire. So of course I started doing more research and found out it could be one of 4 things the spark plugs, fuel injectors, Coils or EGR. So my question is when I take it to the mechanic what should I exactly have them look for. Don't want to get sold a bunch of stuff I don't need any advice ?
     
  2. bisco

    bisco cookie crumbler

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    start with the egr circuit cleaning $1,000. bring them the video from @NutzAboutBolts
    that has to be done regardless.
    pray that the head gasket isn't blown.
    if it doesn't go away, they can swap plug/coil/injector locations to see if the code moves to determine the problem.
     
  3. Seth Holloway

    Seth Holloway Junior Member

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    thanks, I am actually goiing to take it to the Toyota dealer, I live in Alabama and every time I have taken it any other placce around here, they look at and say they have nevveer worked on a Prius before, sso II feel more comfortable taking it to the dealer.
     
  4. abdullah arslan

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    Because of EGR carbon build up, the 2 holes of intake manifold gets clogged earlier and brings about the misfire. The proper way is to clean Egr unit and intake manifold and checking plugs and coils also. The dealer will only replace it, if you don't mind about a thousand maybe more because egr valve and cooler is about 600 bucks both.
    This forum has everything you need for DIY!


    Posted via the PriusChat mobile app.
     
  5. Seth Holloway

    Seth Holloway Junior Member

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    Thanks, I used to be a DYI person, I watched a video on cleaning the EGR, but I am the owner of a small business and care taker of my 87 year old mother who has multiple conditions, her Cadi is in the shop and this is the only other car we have so, I don't really have the time to DYI. If I was younger I would.
     
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  6. Grit

    Grit Senior Member

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    o_O
     
  7. Grit

    Grit Senior Member

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    :eek::eek::eek::eek::eek::eek::eek::eek::eek::eek::eek::eek::eek::eek::eek::eek:
     
  8. rjparker

    rjparker Senior Member

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    I would ask them to diagnose the knocking and give you the verdict. Most dealers will do what you tell them to do but it could easily be a waste of money, especially if major work still has to be done. Many people have spent $1,000-$2,000 only to find the problem is still there. Don't be that guy.
     
  9. Jon Schro

    Jon Schro New Member

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    Is one able to determine whether the problem stems from the EGR circuit by simply unplugging power to the EGR and running the engine?
     
  10. Seth Holloway

    Seth Holloway Junior Member

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    I did unplug the EGR and drove the ccar aa bit and it still rattled, which I saw from videoss on youtube that would mean it waas the manifold intake, buut like I said I am taking it to the dealership and letting them diagnoise the problem, becausse every other mechinc I have taken to around here in Birmingham has scratched their head and said we havn't never worked on a PPrius before, even when I have taken it for an oil change. I got a lifetime warranty from the dealer so I am hoping this is covered.
     
  11. bisco

    bisco cookie crumbler

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    No, the whole circuit would still be clogged
     
  12. abdullah arslan

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    One more thing I can add is to clean the tubes where the coils and plugs go into. It happened to me one time, it was only knocking due to gunk and grease inside. which most probably coming from a clogged Intake Manifold. Just one suggestion, do not add Seafoam or Gumout while it's too dirty, it messes up the ignition
     
  13. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Exhaust Gas Recirculation cleaning info linked in my signature.

    I’d second @bisco : START with the EGR cleaning; with your miles it’s due. Might be overdue. If you can DIY that’s definitely the way to go: much less hassle, more thorough, and virtually no expense.

    @rjparker’s advice to run tests (to determine head gasket integrity) is another thing to do ASAP. Leak-down test is best, for determining if HG is leaking, and how.
     
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