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Head gasket worry

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by C-in-DC, Jul 3, 2024 at 6:13 AM.

  1. C-in-DC

    C-in-DC Member

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    Been having a rough ride lately. Got a Code P0303. Few hours later I got a p0818. Data stream showed the coolant temp at -40 celcius. After purchasing a new engine coolant temp sensor I drove home (about 60 miles) with the check engine light on. When I changed the sensor I realised the connector had a broken wire. I got a new connector pigtail and soldered it onto the harness again. The above codes cleared however the rough engine is still occurring. I’m also smelling a burnt wire smell(maybe just the wires I soldered?)

    When I read my data-stream with a scan tool I’m seeing cylinder misfires but no code is thrown. I’m also seeing the misfires clear in the data stream. Is this possible? Most of the misfires are in cylinder 3 and four. Worried I blew a head gasket because I drove on p0818.
     
    #1 C-in-DC, Jul 3, 2024 at 6:13 AM
    Last edited: Jul 3, 2024 at 6:20 AM
  2. Tombukt2

    Tombukt2 Senior Member

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    This is all real common for this engine so there's always that. It's inspection camera time basically That's the easiest way to rule out all the nonsense or else you go through all the silliness of these tests and what have you and still don't know what you're really looking at. When you look in the cylinder bores. You pretty much get the end all be all definitive answer.
     
    #2 Tombukt2, Jul 3, 2024 at 7:55 AM
  3. Brian1954

    Brian1954 Active Member

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    Did you type the P0818 trouble code wrong? Did you mean P0118 instead?

    Driving around with a P0118 code will probably not cause the engine to overheat. It would not affect the head gasket.

    I do not think the P0118 and the C0303 engine misfires are related. They are two separate issues.
     
    #3 Brian1954, Jul 3, 2024 at 9:02 AM
    Last edited: Jul 3, 2024 at 9:09 AM
  4. Mendel Leisk

    Mendel Leisk Senior Member

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    What’s the miles?
     
    #4 Mendel Leisk, Jul 3, 2024 at 9:18 AM
  5. Eddie25

    Eddie25 Active Member

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    The vast majority of head gasket issues seem to be on cylinder 1 and possibly 2, so at least there's that. If you can watch the misfires on the scan tool I would just start with typical misfire troubleshooting like first swapping coils around, then spark plugs and see if the misfire stays or moves.
     
    #5 Eddie25, Jul 3, 2024 at 10:46 AM
  6. C-in-DC

    C-in-DC Member

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    #6 C-in-DC, Jul 4, 2024 at 12:23 AM
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  7. C-in-DC

    C-in-DC Member

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    Yes I meant p0118. It’s reading properly now. The temp sensor being right against the Egr because of the gen3 to gen 4 new location caused the code. The Egr probably melted the wire and the plastic connector.
     
    #7 C-in-DC, Jul 4, 2024 at 12:27 AM
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  8. C-in-DC

    C-in-DC Member

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    @Tombukt2 is probably right that I need to scope the cylinders.

    can you have a misfire and not get a check engine light? I saw at least 9 while driving in the data stream but no check engine or code In the freeze frame.
     
    #8 C-in-DC, Jul 4, 2024 at 10:40 AM
  9. C-in-DC

    C-in-DC Member

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    would love a confirmation that p0118 won’t cause overheating. I noticed the coolant fan was on anytime the engine was in running. Maybe there’s a failsafe like I read in another thread? I read the ect sensor controls a lot of the engine info like when the fan should turn on and the water pump. Maybe that’s for more modern cars? I figure the thermostat is still opening and allowing coolant to flow.
     
    #9 C-in-DC, Jul 4, 2024 at 10:48 AM
  10. Eddie25

    Eddie25 Active Member

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    I'm pretty sure you can get misfires with no code.

    If you have a borescope, I'd say scope it, but you might as well try swapping coils/plugs as well. Being cylinder 3 and 4 still makes me think it's probably not the HG. Have you changed spark plugs recently (like within the last 30k miles)? Has the intake manifold ever been cleaned out (the EGR runners)?
     
    #10 Eddie25, Jul 4, 2024 at 10:51 AM
  11. Mendel Leisk

    Mendel Leisk Senior Member

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    More’n likely head gasket. EGR and intake cleaned? What was first cleaning, and ditto for any subsequent cleanings?
     
    #11 Mendel Leisk, Jul 4, 2024 at 11:22 AM
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