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New member with P0420 question

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Silent worth, Aug 30, 2023.

  1. Silent worth

    Silent worth New Member

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    II
    Hello all. I’ve been lurking for a bit while attempting to fix my P0420 code on my 2008 with 162k miles and decided it’s time for a post.

    The CEL came on about a year ago (always on, not intermittent), shortly after which my cat got stolen off my car. I thought, great timing! Now I’ll get this taken care of and insurance will cover the replacement. A new cat was put on by a local muffler shop, but the CEL came back on right away. So they put another cat on. Same thing. Then I went traveling for 7 months and came back recently, CEL still on. So I brought it back to the shop and they thought it was the O2 sensors, which were both original and apparently reading incorrect voltages. They replaced both, and the light still came back on after each replacement. They seem pretty lost and not sure what to do next.

    Is it possible the light was originally thrown for a bad o2 sensor, and then they replaced the cat… and then in my 6 months of driving with the new cat and the (possibly) bad o2 sensor that would have ruined the new cat? And now that the o2 sensors have been replaced they’re fine but the light is now on for the damaged cat and that needs to be replaced again?

    Any suggestions where to look next? Thanks.
     
    #1 Silent worth, Aug 30, 2023
    Last edited: Aug 30, 2023
  2. SFO

    SFO Senior Member

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    Welcome to PriusChat!!

    Was the replacement cat an OEM from a dealership? (your insurance should've covered like for like)

    Did the shop replace the A/F sensor and the downstream O2 sensor with OEM from a dealer, or something else?

    Guessing this shop isn't using "techstream" (dealer technician diagnostic software), or even a decent scanner.

    FYI : You're moderated until you've posted 5 times.
     
    #2 SFO, Aug 30, 2023
  3. Tombukt2

    Tombukt2 Senior Member

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    This is what generally puts these cars out to pasture the 18 to1900 cat The $100 plus each sensors and still no resolve or it's very short-lived. Something seems real fishy with this I don't know what it is I just thank God that I am in a non-emissions county so I'm good That's why I buy up these generation twos and run the hell out of them because I can almost everyone I've ever had has the same issue so I don't run down the rabbit hole trying to fix it what you might want to try is the 90° spacer with a piece of catalyst material in it they come pre-made up on Amazon in places out of hard metal it screws into where your downstream O2 sensor goes and your O2 sensor screws into this fixture you just screwed in so it moves the O2 sensor out of the heavy flow of the pipe some people have reported this immediately cleaned up their cell light It is not an illegal piece when installed correctly most places don't even notice it California might then again they might not once it gets dirty I have one sitting here on my table that I've been meaning to get around to putting in I just haven't.
     
    #3 Tombukt2, Aug 30, 2023
  4. Silent worth

    Silent worth New Member

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    the cat was an aftermarket, not OEM. Both o2 sensors were OEM. I’m thinking I should go back to insurance and see if they would still cover an OEM cat replacement now, even through they already paid for a non-OEM one. Seems like a bit of a long shot but worth a try. Strange thing is the P0420 CEL came on before the cat was stolen, and the same light has stayed on since.
     
    #4 Silent worth, Aug 31, 2023
  5. Silent worth

    Silent worth New Member

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    they seem to have a pretty decent scanner but not sure they know how to use it. What’s also strange is they told me they do these stolen cat replacements for lots of Prius owners and don’t have an issue with others having CEL flipping on.
     
    #5 Silent worth, Aug 31, 2023
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    Not quite sure what to recommend here. An experienced technician would use a capable scantool to TEST the Air/Fuel sensor, oxygen sensor, and catalyst functions. Then he would know what part is deficient.

    My P0420 checklist is pretty simple.

    1) NO exhaust leaks anywhere from the engine to past the downstream O2 sensor.
    2) No applicable TSB's for this problem.
    3) No engine misfires.
    4) A/F and O2 sensors work normally (use bidirectional A/F scantool test on Toyotas) - Total fuel trims under all conditions is near 0% (+/- 10% max).

    (5) "Excessive" oil consumption - burning will drastically reduce the new cat's lifespan.

    If all that's "good", then the car needs a cat.

    Posted via the PriusChat mobile app.
     
    #6 mr_guy_mann, Aug 31, 2023
  7. golfmk681

    golfmk681 Active Member

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    Can you post a link to this product?
     
    #7 golfmk681, Sep 3, 2023
    Tombukt2 likes this.
  8. golfmk681

    golfmk681 Active Member

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    Ok I have excessive oil consumption. Does that mean I need to take my car out to the back of the barn and put it out if it’s misery? My cat a aftermarket noncarb and with excess oil consumption I don’t feel oem cat is worth it. Ugh
     
    #8 golfmk681, Sep 3, 2023
  9. mr_guy_mann

    mr_guy_mann Senior Member

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    It means that any converter you install will likely have a short life before oil combustion residue renders it "nonfunctional".

    Some people will choose to live with the CEL on (if local inspections don't get in the way). Others will install cheap converters as needed. Some might decide to repair or replace the engine. Or move on to another car.

    Posted via the PriusChat mobile app.
     
    #9 mr_guy_mann, Sep 4, 2023
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