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P0420, could it not be the catalytic converter?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Joao, May 17, 2023.

  1. Joao

    Joao Junior Member

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    Hello everyone.
    Trying to diagnose p0420 here. It seems to point at failed cat (it is aftermarket).
    However, reaseaching this i found that the airflow sensor voltage is constantly higher than it should (i think), it sits around 3.9v on steady power, instead of 3.3. While the o2 sensor jumps between 0.1 and 0.9. Should i go ahead and replace the cat or there may be something weirder going one?
    Torque pro pics attached
    Thanks
     

    Attached Files:

  2. SFO

    SFO Senior Member

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    How old are the existing sensors, or were they also replaced with aftermarket parts?
     
  3. Joao

    Joao Junior Member

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    I believe They are all the originals oem
     
  4. Tombukt2

    Tombukt2 Senior Member

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    So this cat on the car right now used to not have this code and no code and was working fine this aftermarket cat?
     
  5. Tombukt2

    Tombukt2 Senior Member

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    Oh and do you have any idea how long it was on the car working like weeks months
     
  6. Joao

    Joao Junior Member

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    It was working fine for 6 or 7 months since i installed it
     
  7. SFO

    SFO Senior Member

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    Sensors don't last forever, and if over 250km now might be a good time to replace the upstream sensor with OEM or Denso.

    If the catalytic was stolen, they usually take one of the sensors with it.
     
  8. Joao

    Joao Junior Member

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    In my case they didnt, as they only cut the cat further back. Is there any indication that the sensors are bad based on the data above?
     
  9. Georgina Rudkus

    Georgina Rudkus Senior Member

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    The vibration from a sawzall might likely destroy an oxygen sensor.
     
  10. SFO

    SFO Senior Member

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    How many kilometers are on the vehicle (or A/F sensor)?

    The A/F sensor may have a short circuit, you can use the workup below to determine if it needs replacement.

    Here is the workup for P2195 : https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/Prius%20Service%20Manuals%202004/%E4%BF%AE%E7%90%86%E6%89%8B%E5%86%8C/04pruisr/05/2054m/cip2195.pdf

    Here is the workup for P0420 : https://attachments.priuschat.com/attachment-files/2017/02/120177_p0420.pdf
     
  11. mr_guy_mann

    mr_guy_mann Senior Member

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    I would try a different scantool app to confirm those A/F and O2 readings.

    On my 2006 with 205k at steady cruise, A/F is around 3.3V, O2 is around 0.7V, short and long term fuel trims are 0 +/- 5%.

    IF your A/F is actually near 4.0V and it's telling the truth, the engine is really lean- O2 should be near 0V and fuel trims should be high (+)%.

    IF the A/F is actually near 4.0V but it's lying, the engine is really rich- O2 should be near 1.0V and fuel trims should be high (+)%.

    IF fuel trims are near 0 and the O2 is moving (0.1V to 0.9V) then Torque is lying about the A/F value.


    P0420:

    NO exhaust leaks from the exhaust manifold to 18" past the O2 sensor (not even a pinhole)- I find only a dealer gasket will reliably seal the spring bolt joint at the manifold).

    NO misfires, fuel trims near 0, A/F and O2 sensors can report "full rich to full lean".

    No excessive oil burning (will "kill" the cat fairly quick).

    If all that's ok, then I put a "good" cat in (preferably OE).

    Posted via the PriusChat mobile app.
     
  12. Joao

    Joao Junior Member

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    Thanks. Fuel trims are around 2.5 (long term) and short term varies from -4 to +4.
    No leaks, and i believe no misfires. I am inclined to go for the cat.
     
  13. SFO

    SFO Senior Member

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    Please report back in this thread with any updates.
     
  14. Joao

    Joao Junior Member

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    Cat replaced.
    Error and engine light are gone.
    Lets see how long this one lasts
     
    mr_guy_mann likes this.
  15. mr_guy_mann

    mr_guy_mann Senior Member

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