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Check Engine Light and Engine Misfires / O2 Sensor

Discussion in 'Gen 2 Prius Technical Discussion' started by TexasZ, Feb 13, 2023.

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  1. TexasZ

    TexasZ Junior Member

    Joined:
    Oct 8, 2017
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    Location:
    Houston
    Vehicle:
    2008 Prius
    Model:
    II
    Recently got a check engine light and went to my local auto zone to get the codes pulled. Need to pass inspection soon.

    Looks like I have multiple problems, first with cylinder misfires and second an O2 sensor. My 2008 Prius has about 180K miles on. Replaced the spark plugs with OEMs at about 110K miles.

    Codes are P0300/PO301/PO303 (Cylinder 1 and Cylinder 3 misfire detected)

    Question is: Will replacing the spark plugs likely solve the problem or do I / should I replace the ignition coils as well? Coils have never been replaced. The Toyota coils are about $100 each at the dealer wholesale parts store. Can get aftermarket for $50 to $60 each. If I should replace the coils, is it worth it to spend the extra $ to buy the Toyota coils, which are about twice as much?

    On the O2 sensor, code is P0137 - Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 2). I think I just need to replace the sensor as I don't think it's ever been replaced. Same question on Toyota vs aftermarket O2 sensor. Is it worth the extra $. I think this is the downstream sensor. My cat converter was stolen about a year ago. Replaced with after market and has worked fine since.

    Grateful for any advice. My Gen 2 is 15 years old and running strong but thinking about trading it in. Hence questions on whether worth it to buy OEM parts versus aftermarket.

    Thanks a ton.
     
    #1 TexasZ, Feb 13, 2023
  2. mr_guy_mann

    mr_guy_mann Senior Member

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    Vehicle:
    2006 Prius
    Model:
    Four
    There can be dozens of reasons why the engine sets misfire codes. Failed ignition parts are very common, esp at high mileage. For most people it makes sense to replace ignition parts and see how it goes. There might be something else wrong, but you have to know that the ignition parts are good.

    Personally, I would just replace the spark plugs and all the coils. Use NGK or Denso plugs, and Toyota or Denso coils. Get parts from a brick and mortar store or a reputable online source - not amazon or ebay. Counterfeits are a known problem.

    I have been "bitten" by crappy aftermarket parts way too many times. They fall into my "use them only if there is NO other options" - and know they can (will) fail again".

    If budget is super tight, do the plugs, but swap the coils around - # 1 & 3 with # 2 & 4. Then see if the misfire codes return - and if they follow the coils. If so, then replace the bad coil(s), but be aware that the others could also fail at any time.

    Also clean the throttle body and the MAF sensor.

    Fix the misfire first, then see what the downstream oxygen sensor does. Again, if it is bad I would only use Toyota or Denso (or NTK if that's what's available).

    Posted via the PriusChat mobile app.
     
    #2 mr_guy_mann, Feb 15, 2023
    Last edited: Feb 15, 2023
    vvillovv likes this.
  3. TexasZ

    TexasZ Junior Member

    Joined:
    Oct 8, 2017
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    Location:
    Houston
    Vehicle:
    2008 Prius
    Model:
    II
    Exactly what I needed. Thanks sincerely for taking the time for the response and advice. Going with OEM parts and moving out to see if that resets the codes. Many thanks!
     
    #3 TexasZ, Feb 16, 2023
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