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P0420, CEL, Bad mpg

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by DnDnDnDnd, Mar 22, 2021.

  1. DnDnDnDnd

    DnDnDnDnd New Member

    Joined:
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    Location:
    Seattle Wa
    Vehicle:
    2009 Prius
    Model:
    I
    Hi everyone
    I just bought a 2009 Prius a couple weeks ago.
    My CEL came on a couple days ago and turned off this morning.
    got the P0420 code and been getting average just city driving low 30's to 29 mpg.
    Got it up to 34 by driving to get vaccinated this weekend (Hour drive freeway)
    just changed the 12v battery and gonna do spark plugs this weekend.
    Wondering if my Cat is actually failing, anyone had the same issue by chance?
     
    #1 DnDnDnDnd, Mar 22, 2021
  2. JC91006

    JC91006 Senior Member

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    Location:
    Los Angeles, CA
    Vehicle:
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    Sell the failing Cat for $900 and buy an aftermarket one for $300. You'll be ahead and your P0420 will go away
     
    #2 JC91006, Mar 22, 2021
    DnDnDnDnd likes this.
  3. davecook89t

    davecook89t Senior Member

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    Location:
    Washington State, Florida
    Vehicle:
    2017 Prius
    Model:
    Four Touring
    The CEL on our Gen 2 is coming on every couple of weeks with a P0420, but then it will turn off on its own again a few days later. Our winter time MPG in NY is not too much different from yours. When we take it on the highway back to Florida, it comes back to the mid 40s. I'm pretty sure changing the catalytic converter would make no difference MPG-wise. I will not be removing the OEM cat. With 291k miles, we expect to be giving the car to charity shortly, as soon as the HV battery fails. We will let them get the benefit from the OEM cat. Hopefully, it won't get stolen first.;)
     
    #3 davecook89t, Mar 22, 2021
    DnDnDnDnd likes this.
  4. DnDnDnDnd

    DnDnDnDnd New Member

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    Location:
    Seattle Wa
    Vehicle:
    2009 Prius
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    I
    LOL! Not a bad idea. I'm thinking I'll probably change it. Could that also be why my MPG is suffering so much?

    I use to have a 2004 with 215k and got low 40s, you getting mid 40s makes me jealous
     
    #4 DnDnDnDnd, Mar 23, 2021
    Last edited by a moderator: Mar 23, 2021
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