P0304 then P0354 blues

Discussion in 'Gen 2 Prius Main Forum' started by James1964, Oct 12, 2020.

  1. James1964

    James1964 Member

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    2005, 245K miles, gets about 45mpg, reliable, daily runner: every 5 months or so the ice will run rough and may throw a P0304 code. I run a can of Amsoil Deep Creep through the manifold and work a local hill climb and that will clean up the misfire and the code, temporarily. P0304 points to #4 cylinder so I replaced that original coil along with all 4 spark plugs. She started up, ran fine but in a few miles, red triangle, P0354 code, no ICE. Pulled over. Checked all the coil connections and the wiring harness (looks like it sounds). Would power up and ICE would start up, sputter, quit. AAA towed back to my driveway safely.
    Any helpful thoughts, recommendations are appreciated in advance.

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    #1 James1964, Oct 12, 2020
    Last edited: Oct 13, 2020
  2. James1964

    James1964 Member

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    #2 James1964, Oct 12, 2020
    Last edited: Oct 13, 2020
  3. mr_guy_mann

    mr_guy_mann Senior Member

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    My first thought is if you replaced some parts after which things got worse, then maybe the part you installed is bad. Can happen. I have pretty much given up on most aftermarket brands due to unknown quality. For Toyota I prefer OE or Denso (the OE supplier).

    On some of these year Toyotas the ecm will shut down the fuel injectors if it doesn't get a good feedback signal from each coil.

    One thing to keep in mind is the state of charge left in your hv battery. Everytime you try to start the engine that will use up more juice and eventually you will be stuck with a discharged hv battery. Very few people have a means to recharge it so that would be game over. Also be aware that when the prius tries to start it spins the ICE at 1000 rpm for several seconds, so what sounds like a start and stall, might really be a crank-no start.

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  4. James1964

    James1964 Member

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    Ugh. So the discharged hv battery just moved to first position. Your sequence makes perfect sense: multiple starts totally discharge the hv, game over. This car was running great, perfectly reliable b4 I changed spark plugs and the one coil (P0304). What a bummer.

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  5. jburg

    jburg Member

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    Did you replace the coil with a Denso OEM unit?
     
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  6. James1964

    James1964 Member

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    Yes, DENSO OE coil but I hear those can be counterfeit too. I may throw the old coil back in there and see what happens. She was running before fine.

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  7. jburg

    jburg Member

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  8. James1964

    James1964 Member

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    Update: I slept on this problem for more than one night but a solution did come eventually. I reinstalled the old coil, cleared the codes and took the risk of starting it up again. It was at the last absolute pink bar so I was completely concerned that I might discharge the HV battery to 0 and be in a fix. She started after the code clearing and ran long enough to give me hope. I ran the codes again and it pointed to the MAF sensor although I forget that code now. Anyway, I removed the MAF sensor (two Phillips screws), sprayed a good 10 sec stream of MAF cleaner, waited a min, reinstalled and CAR STARTED UP, ICE CHARGED UP TO FULL GREEN, RUNNING GREAT FOR WEEKS NOW. Moral of the story: start with the MAF cleaning and NEVER GIVE UP.

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  9. mr_guy_mann

    mr_guy_mann Senior Member

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    When you used cleaner on your MAF, did you shoot it inside at the two little sensor resistors? Hard to see if you don't know that they are there. DSC_3737~2.JPG

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  10. James1964

    James1964 Member

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    Unfortunately it's the end of the road for this old girl. She saved my son's skin as her final act though. Thank you Toyota for being crazy enough to create this magnificent vehicle. 20201214_122442.jpeg

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  11. jburg

    jburg Member

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    Dude, sorry to hear that. Take out the catalytic converter and sell it on Ebay for $1200.
     
  12. MikeV

    MikeV New Member

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    i just got same code - not really mechanically inclined car wise but can do simple things after an explanation video. Are you saying that cleaning the maf sensor was the culprit and that too care of the problem? Do you have vid or sourse to look at how its done (will check ytube) also do you rteset code or once fixed will code reset on its own.
     
  13. ChapmanF

    ChapmanF Senior Member

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    Please forgive me for checking to make sure, but are you saying you literally got the same two codes, P0304 and P0354?

    P0304 is a generic code indicating that the engine is misfiring in cylinder 4 for some reason. You'd be missing the point if you read somebody else's thread where the reason for them turned out to be the MAF sensor and expected that to mean your car has the same problem. The point with a P0304 is you have to find out why your engine is misfiring there, and then fix that. Fuel, compression, and spark are the main things to check.

    If you really do also have the P0354 code, that indicates a problem with an ignition coil. Most likely #4, but the ignition feedback circuit is shared by all four, so on rare occasions weirder things can happen.
     
  14. MikeV

    MikeV New Member

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    no just the p3034 code as of wed this week but for the las 3 months the mpgs dropped from about 45 to 40.
     
  15. MikeV

    MikeV New Member

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    no just the p3034 code as of wed this week but for the las 3 months the mpgs dropped from about 45 to 40.
     
  16. ChapmanF

    ChapmanF Senior Member

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    Just the P-what? That would be a whole 'nother code.
     
  17. MikeV

    MikeV New Member

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    meant 0304
     
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