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.
     
  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?
     
  3. George W

    George W Active Member

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    Are O2 sensors supposed to be changed in pairs, so that they match?
     
  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.
     
  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.
     
    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.
     
  7. lexidium

    lexidium Junior 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 . . . . .
     
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