P0420 Catalyst System Bellow Threshold Bank 1?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by KitsuneVoss, Jan 25, 2025.

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  1. MCCOHENS

    MCCOHENS Active Member

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    ok, first off be very careful on "cheap" parts as sometimes they are crap. On O2 sensors, buy name brand with the plug attached. Sometimes the instructions are wrong which can lead to killing the ECU. BTDT. I would try the cat additive and also consider pulling the MAF and cleaning it with MAF spray cleaner. It is easy, may require a torx bit but worth having as the MAF cleaning should be an annual thing. Also, if it the O2 sensor does turn out to need replacement proceed carefully. They can be rather tough to break loose and have been known to strip out the threads in the pipe.
    On oil consumption, with your mileage if the car was not well maintained it may just be a worn out motor. Some will try an oil ring cleaning procedure, which is cheap but time consuming. You can find lots of BTDT on this forum.
    Hope this helps more than some of the other posts!
     
    #21 MCCOHENS, Jan 27, 2025
  2. rjparker

    rjparker Tu Humilde Sirviente

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    I did not say it has to be welded. Reread.

    None of the cat or oil burning additives work. However a clogged cat can cause engine failure and fires.
     
    #22 rjparker, Jan 27, 2025
    Last edited: Jan 27, 2025
  3. saneesh8

    saneesh8 Junior Member

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    Catalytic converter on ebay is ~$100 with 5 year warranty. Rock auto have it for ~$250.

    Does any one tried any of these after market brands?
     
    #23 saneesh8, Jan 29, 2025
  4. KitsuneVoss

    KitsuneVoss Member

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    A minor update. My oil was low when I checked the dipstick a little while back, likely at least two weeks back although maybe even three weeks. I did not check afterwards but likely added about two quarts. Likely driven anywhere between 700 and 1050 miles between then and now. Checked it just now and the oil level is still pretty high so I don't think the engine is burning excess oil.

    Have not interrogated the computer yet. Have so many things on my plate that I often lose track of things.
     
    #24 KitsuneVoss, Feb 9, 2025
  5. KitsuneVoss

    KitsuneVoss Member

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    Some minor updates and questions. I have a new catalytic converter I got from Rock Auto. Figured more trustworthy than eBay and decided to order it before tariffs make prices go insane.

    I do know of an old man who used to work on exhaust systems. He was cheap but did a good job. He is a short "Prius" distance from home even though I moved. Figure check if his shop is still where it was. If I can get him to weld it, should I?

    Also, if I remove it myself, I know someone who welds. In such a case, would I be better off getting it welded by him or better off clamping it? Concerned that if the fitting is not perfect and welded, might not fit?

    Also, if I end up doing it myself, I have a grinder. Would that work for cutting the pipe or would I be better off getting a reciprocating saw as is used in this video at the 7:00 mark?



    Also, I want to clean the intake system a bit. I was thinking about spraying to down at least real well with throttle body cleaner. I have removed throttle bodies in other cars to clean them but would prefer to wait on that. There is a video where the person did not want to push on the throttle body to get the underside. Is that an actual concern?
     
    #25 KitsuneVoss, Apr 30, 2025 at 10:38 AM
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