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Lower fuel economy after CAT replacement

Discussion in 'Gen 2 Prius Fuel Economy' started by Gecko19, Jan 5, 2020.

  1. Gecko19

    Gecko19 New Member

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    Hello All,

    I have a gen 2 Prius with 105k miles on the clock. The catalytic converter on the car was stolen along with the 02 sensor. My local garage replaced the catalytic converter and the rear exhaust box(since it was corroded) along with the O2 sensor -- all after market parts. I noticed that 2k miles after the car chnage the mileage I get from a tank of fuel has dipped and also, the car seemingly is a bit more quicker to drive than what it used to be(before the cat got stolen) -- any ideas if the after market O2 sensor could be the culprit here, or is it just the winter(which is not bad and temps are in the lower 10 degree C). The cars 12 V battery was replaced 2 years ago .

    By dip in fuel mileage I mean from a consistent 51 mpg to consistent 45 mpg.
    Cheers,
    G.
     
    #1 Gecko19, Jan 5, 2020
  2. valde3

    valde3 Senior Member

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    Almost impossible for the new converter or rear oxygen sensor to reduce your actual fuel economy. Most likely just a coincidence and/or maybe you're driving it harder now?
     
    #2 valde3, Jan 22, 2020
  3. George W

    George W Active Member

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    Are O2 sensors supposed to be changed in pairs, so that they match?
     
    #3 George W, Jan 22, 2020
  4. valde3

    valde3 Senior Member

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    No. And Prius does actually have air fuel ratio type sensor in the front. Rear sensor is oxygen sensor and is mostly used just to check that catalytic converter works.
     
    #4 valde3, Jan 22, 2020
  5. audiodave

    audiodave Active Member

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    Mine did that too. But my freeway milage is great. I'm curious how my fuel trims look, I'd bet its off from the normal range and I've considered replacing the front O2 sensor. After 260,000 miles the accuracy has to be a little off.
    Posted via the PriusChat mobile app.
     
    #5 audiodave, Jan 23, 2020
    George W likes this.
  6. audiodave

    audiodave Active Member

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    I also notice my oil get dirty fast too like the fuel trims are high. Maybe the rings I don't know.
    Posted via the PriusChat mobile app.
     
    #6 audiodave, Jan 27, 2020
  7. lexidium

    lexidium Active Member

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    Strange. After I had new cat and sensor (same reason) I'm under the impression that I get a bit more. Aftermarket parts as well.
    It's probably just psychological . . . . .
     
    #7 lexidium, Jan 27, 2020
  8. Pezzie

    Pezzie New Member

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    I also had my cat and O2 sensor replaced. City mileage dropped approx. 8mpg!!! Highway mileage dropped just 3mpg or so, if that.
    Toyota never warned me about this. I called the dealer when it got ripped out by thieves. Only after I had it replaced by my standard mechanic did the dealer then say “Oh yeah, that happens with the after market. It’s illegal to resell your Prius in California now.” Um what?

    Naturally, with no info at the get go I chose the$1200 fix to replace vs Dealer’s $2900 one.

    Toyota needs to offer catalytic converter replacement and cat guards at reduced cost. Older Prius’ are sitting ducks.

     

    Attached Files:

    #8 Pezzie, Mar 26, 2021
  9. shane fast

    shane fast New Member

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    Is Denso the OEM manufacture for the 02 sensors? Does anyone know.
     
    #9 shane fast, May 3, 2022
  10. dolj

    dolj Senior Member

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    Yep.
     
    #10 dolj, May 4, 2022
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