P0301 misfire on cylinder one

Discussion in 'Gen 2 Prius Main Forum' started by danielz000, Nov 23, 2025.

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  1. PrimalPrius

    PrimalPrius Junior Member

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    The pieces on my car definitely look different, with the most notable difference being that there are drain holes on both sides of the divider. Only 2 on the passanger's/right side (US) of the divider and at least 6 on the drive's/left side of the car.
    I would take it apart again to verify where the water would go if you were to add drain holes there.
    Seems like an odd setup for stock. My car, a US 2009 would not be capable of having the water issue (unless the holes were blocked).
     
    #21 PrimalPrius, Feb 16, 2026 at 12:43 PM
  2. PrimalPrius

    PrimalPrius Junior Member

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    On my car those drain holes are on the bottom surface.
     
    #22 PrimalPrius, Feb 16, 2026 at 12:44 PM
  3. BiomedO1

    BiomedO1 Senior Member

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    That may be an aftermarket cowl, that someone replaced - because they broke the old one when replacing the windscreen????
    I too never had an issue with water pooling there, unless it was stopped up with leaves and debris. That would be a common sense issue while engineering the car. IMHO; dumping any liquids directly on top of the ignition coils would be a major faux-pas and can cause intermittent misfires when the current gets discharged into the spark plug well walls instead of the other end of the spark plug.

    Just my 2-cents....
     
    #23 BiomedO1, Feb 16, 2026 at 12:58 PM
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  4. PrimalPrius

    PrimalPrius Junior Member

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    Yes, aftermarket cowl makes much more sense... would be interesting if more of those who drive on the wrong side can chime in and say what their parts look like (and if known to be OEM and what year).
     
    #24 PrimalPrius, Feb 16, 2026 at 1:07 PM
  5. BiomedO1

    BiomedO1 Senior Member

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    LoL; "wrong side" LoL;):p:cool::LOL::ROFLMAO::whistle:; as you stated, they are right drive in Japan..... so that problem shouldn't exist - unless they wanted to give the "middle-finger" to the imperialist UK.:(:whistle: More than likely an aftermarket part that missed the weep holes when the OEM plastic was scanned. It takes real effort to perfectly duplicate a part.:sleep:
     
    #25 BiomedO1, Feb 16, 2026 at 1:15 PM
  6. danielz000

    danielz000 Junior Member

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    Have you got a picture of yours PrimalPrius? That'd be interesting to see!

    My dad owned the car from new. If it was an aftermarket part someone slipped it in without say anything to him about it. It was serviced by Toyota for most of its life too.

    With that said, it's a 2005 model. He bought it before they were popular in the UK, so maybe Toyota addressed the issue in later models.

    I could drill some more holes on the bottom, I think that would be safe if they're towards the back but I think the 3 I drilled should be enough. Looking at the design, with the bonnet closed I'd say 90% of the rain will drain off somewhere else.
     
    #26 danielz000, Feb 16, 2026 at 1:34 PM
  7. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Get out the power drill? :whistle:
     
    #27 Mendel Leisk, Feb 16, 2026 at 2:16 PM
  8. dolj

    dolj Senior Member

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    Interesting discussion about the cowl, but this does not address the issue of water spilling over where the coils are, which should not be happening regardless of how much water is in that channel.

    It would seem the rubber seal strip that runs along the front of the cowl channel is leaking. The seal should be tightly against the hood when it is down, and no water should be leaking into the engine compartment. Check the seal. It may need replacing. The hood is not deformed in any way, is it?
     
    #28 dolj, Feb 17, 2026 at 5:32 AM
  9. danielz000

    danielz000 Junior Member

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    Hi All,

    So the car was fine for a day or so, then the misfires came back... No idea if water found it's way in again, I'll have to pull coil pack out and check.

    If not, maybe the spark plugs has perished due to the misfires or something...

    Dolj, the strip looks fine to me... I did give it a clean up top and bottom whilst i was there.... Oddly I noticed on the UK passenger side, it unclipped without a problem, the full length. On the UK drivers side, it mostly unclipped but seemed to be glued on parts... No idea if thats normal. With that said though, I imagine that even if that if that rubber strip is working fine, the water would overflow between the 2 sections of the cowl and make it's way down to the spark plugs... Also, I imagine that strip is only designed to stop splashes and not hold water permanently... Also, even if it was perfectly water tight, opening the bonnet would allow the water to flow in...
     
    #29 danielz000, Feb 19, 2026 at 9:55 AM
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