P0301 DTC, 210k mi. Still has Orig. plugs: Replace all Coils too?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by davekro, Feb 1, 2026 at 7:03 AM.

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  1. davekro

    davekro Member

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    This is embarrassing. I have never changed the plugs in my wife's 2013 Prius Plug-In (purch. new 10/23). Her last trip to do errands, it jerked aggressively she said, one time when she was accelerating normally (straight). I scanned for codes. My Autel MK 808S shows 4 Faults, all P0301 Cyl. 1 Misfire detected (1 each as Pending, Current, Permanent, and History. I was aghast when I checked my service log, and saw that I had never changed the spark plugs (I see NOW, due at 120k!). So, of course I will be changing the plugs.

    Sounds like there is a decent chance that Cyl 1's coil may be bad. Chat GPT said after changing the plugs, swap Cyl. 1 & Cyl. 2's Coils, to see if the DTC moves to Cyl. 2. Good for troubleshooting the immediate failure, BUT.. Chat GPT mentioned that plugs with 200k+ miles, with worn wider gaps, "...causes Increased firing voltage demand on the coils. 120k–180k miles → common first failure. 200k+ miles → failure is not surprising at all. At 210,000 miles, original coils are officially on borrowed time. So yes — Cylinder 1’s coil being weak or failing is absolutely plausible.

    So should I just bite the bullet and replace all four coils, as they may all be on their last legs by the higher current demand they have been working harder than normal to supply to jump the wider gaps?

    Any particular Spark Plug brand(s) recommended, or brands to especially avoid?

    I see coils going for between $35 to $75, or even $125 each for Denso. On the other hand, I also see
    BDFHYK Ignition Coil Pack UF596 and Iridium Spark Plugs, set of 4 each for $47.69! #1 Best Seller, 4 stars, (4,300 reviews), 100+ bought in past month. That price seems WAY to cheap. Maybe those are shops buying, not DIY people putting them in their own cars??

    Any recommendations for quality Coils at reasonable prices? Are 4 plugs + 4 Coils kits worth even considering? I have only seen no-name combo kits.

    With the time involved to remove wipers, plastic and metal cowls, I want the replacement plugs and coil(s) if installed to last a long time. ;o)
     
  2. ASRDogman

    ASRDogman Senior Member

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    383,000 plus miles on my original coils.....
    Have you just replaced the plugs? That would be the smart thing to do. Then see if you still get misfires.
    You can also move the coils to see if changes.
     
  3. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    Even the dinky battery in the G3 PHEV can keep the engine off enough for a 200K car to have plugs that probably should be replaced but are not as worn as a wireless G3.

    Don't sweat it.
    Replace the plugs.
    Keep the coils, swapping #1 with #2 for troubleshooting.
    You may have larger problems than worn plugs or a sketch coil and so you're going to want to trade time for money in this case if you can DIY.

    Avoid Amazon's and Ebay's infamous CCP sourced "Non OEM genuine" plugs.
    (EVERYONE KNOWS NOEM underperforms and can cause no end of trouble!!!)

    This is the one example that defines the rule of exceptions for getting OEM parts from the stealer.
    Or is it the exception to the rule?

    CURSE YOU self-referential logical paradox!!! :ROFLMAO:
     
  4. Mendel Leisk

    Mendel Leisk MMX GEN III

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    While spark plug would seem a likely suspect, gen 3's are prone to head gasket failure, odds getting better around 150k miles, and near-certainty over 200k. It usually starts on cylinder one (leaking coolant into cylinder), and throws code P0301.

    Has the EGR (Exhaust Gas Recirculation system ever been cleaned?

    Is engine coolant level stable in the reservoir?

    Any cold-start shakes?

    Obviously plugs are overdue, but that, or a coil, may not be source of the code.