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p0420 question

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by twj815, Jul 22, 2024 at 4:06 PM.

  1. twj815

    twj815 New Member

    Joined:
    Dec 25, 2023
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    Location:
    Mahomet, Il
    Vehicle:
    2008 Prius
    Model:
    N/A
    My 2008 Prius now has 268,000 miles on it. Last fall, at around 245,000 miles, someone stole the catalytic converter while it was parked in a retail parking lot. They also cut off the downstream O2 sensor. Insurance replaced most of the exhaust system including both sensors. Now the check engine light comes on showing a p0420 code shortly after starting a cold engine. If I let the engine to warm up before resting the code, the check engine light will stay off for 100 miles or more until after I park the car and allow it to cool down. After the cool down period of half an hour or longer, the check engine light will come back on with the same code.

    Live data with a Blue Driver code reader looks like the downstream sensor is fairly stable in the .6 to .8 volt range on the highway. I occasionally see a momentary drop to near 0 which seems to usually happen while driving down hill. Maybe the engine temporarily shutting down? In town, stop and go driving is hard to tell what the live data is telling me because of the engine starting and stopping all the time.

    Could the new cat have gone bad that quickly? Is it more likely a problem with the downstream sensor? On other cars I didn't care about a p0420 code but since this car doesn't have a temperature gauge, I won't know if there is a problem with the cooling system or other issues if I can't get the check engine light to stay off.

    Thanks for your advice.
     
    #1 twj815, Jul 22, 2024 at 4:06 PM
  2. Tombukt2

    Tombukt2 Senior Member

    Joined:
    Nov 29, 2020
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    1,589
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    Location:
    Durham NC
    Vehicle:
    2009 Prius
    Model:
    Base
    If it was replaced with a factory Toyota cat because you have emissions where you're located then more than likely you have the proper cat and everything should be good with that unless you're burning lots of oil putting that into the cat and then that destroys the catalytic material I don't know generally generation twos don't burn tons of oil not the kind that floods a converter and where is it out in short order generally speaking so it'll be interesting to see what's going on or is this one of those $100 converters which even those they're made by a big company that makes converters for V8 cars and all that kind of stuff so they get decent reviews for all kinds of models not sure about the Prius but they sell for lots of vehicles the kind that kids put flowmasters on and all that stuff so I put a cheap set of cats on a Mercedes and they lasted a long time so there's always that I do realize the Prius cats have a lot more material in them than other cats do or might have oh well
     
    #2 Tombukt2, Jul 22, 2024 at 8:15 PM
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