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Faults PO420 (catalyst system efficiency below threshold) .

Discussion in 'Gen 3 Prius Main Forum' started by dgm1214, Sep 15, 2024.

  1. dgm1214

    dgm1214 Junior Member

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    This popped up after replacing both oxygen sensors, on a 2013 with 177k miles. Prior error was related to faulty downstream oxygen sensor, and found wires from connector damaged. Did this work myself with sensors off Amazon, about $40 each.
    Wondering if I did something wrong ?
    Thanks !
     
    #1 dgm1214, Sep 15, 2024
  2. dgm1214

    dgm1214 Junior Member

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    Update, reset codes again, and after 50 miles NO codes popped up. Will test drive tomorrow too.
     
    #2 dgm1214, Sep 15, 2024
    bisco likes this.
  3. bisco

    bisco cookie crumbler

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    good luck!
     
    #3 bisco, Sep 16, 2024
  4. dgm1214

    dgm1214 Junior Member

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    Update2. Drove only about 5 miles today before engine light appeared. Same 2 codes as before

    1) P0420 catalyst system efficiency below threshold Bank 1
    2) vehicle has no faults

    wondering why it says ‘no faults’ when it reported a P0420.
    Not sure if I should drive it on a trip, 700 miles one way into Canada, or not.
    Thanks for suggestions.
     
    #4 dgm1214, Sep 16, 2024
    Last edited by a moderator: Sep 16, 2024
  5. bisco

    bisco cookie crumbler

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    were the new sensors oem?
     
    #5 bisco, Sep 16, 2024
  6. MAX2

    MAX2 Member

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    How did you read the errors from the machine? Program? Scanner?

    The error of low efficiency of the catalyst is most often critical for the environment and sensitive sense of smell.
    The exhaust pipe smells like donkey urine.
    The car continues to drive without any problems.
     
    #6 MAX2, Sep 17, 2024
  7. AzusaPrius

    AzusaPrius Senior Member

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    Try a bottle of Cataclean that stuff works.

    Also using your car while this code is on is not good for the ICE as it can cause back pressure and ruin your engine.

    If it is original OEM cat then it is time and most likely it is bad as they do not last more than 7-10 years.
     
    #7 AzusaPrius, Sep 17, 2024
  8. Eddie25

    Eddie25 Active Member

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    You generally never want to get important engine management parts like o2 sensors from Amazon.

    I'd be skeptical that the original code was for sure related to a faulty downstream sensor. What code, and how did you come to that conclusion? Could it have JUST been the damaged connector? If feasible, put the old sensors back in with a repaired connector and see what happens.
     
    #8 Eddie25, Sep 17, 2024
  9. dgm1214

    dgm1214 Junior Member

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    Update
    After getting engine light and finding PO138 (bad downstream sensor) on this 2013 with 180k miles, I changed downstream sensor and then received a PO420 (catalytic converter error). So I changed the upstream sensor, and the catalytic converter. Still got the PO420 code. Cleaned EGR and cooler, intake manifold, pcv. No change. Also, the car has never used oil that I could tell, and radiator fluid alway full, and tonight I got 59.9 mpg on a 40 mile errand. The car has been flawless. I lost trust in the local Toyota dealer.
    Now
    I have a 1000 mile trip I need to take. Should I rent a car or drive it ?
    Thanks
     
    #9 dgm1214, Sep 22, 2024
  10. dgm1214

    dgm1214 Junior Member

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    If I remember right, all the wires were intake, but one of the bare wires was touching metal from the frame/holder.
     
    #10 dgm1214, Sep 22, 2024
  11. Eddie25

    Eddie25 Active Member

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    p0138 is a o2 sensor high voltage code. I'm pretty sure this is what you might get if you had a broken wire or bad ground, so in conjunction with visually damaged wiring I would assume they are related.

    To have a sensor cause that code I think it would need to be open circuit. What is the resistance across the o2 sensor you took out?

    I still think you should either get OEM sensors, or repair the old ones and put them back in, (assuming the resistance checks out). I wouldn't feel comfortable diagnosing a p0420 until then (besides maybe visually looking for an exhaust leak or something).
     
    #11 Eddie25, Sep 22, 2024
  12. dgm1214

    dgm1214 Junior Member

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    I measure 15 ohms when testing the black wires on o2 sensor.
    Found an OEM o2 sensor, ordered it. Plan to stay home another week.
    I do not smell any unusual odor at exhaust.
    Thanks
     
    #12 dgm1214, Sep 22, 2024
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