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Unique cat question

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Sina Drums fan, Sep 18, 2021.

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  1. Sina Drums fan

    Sina Drums fan Junior Member

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    I am wondering if running with a new aftermarket catalytic converter without the rest of exhaust would be expected to trip any codes.
    A little history. It's an 08 with 228000. Sold to us as touring but has regular wheels so it might not be but has leather and upgraded radio and fog lights. Got with 150 and had it for a few years. Burning a little more than a quart for 3,000 miles. I've been ignoring codes 0031 2195 2237 and 0138 pending. So I changed out O2 sensors with denso 234-4623 + 234-9056 and immediately got the code for the catalytic converter. I reset it and it tripped again the next day. My goal is to just pass inspection one more time in 3 months. so my question is just if I put on the new aftermarket pipe with the two cats on it would I expect it to run okay and not trip any codes if it's working right of course it won't have the back pressure of the resonator and muffler. I'm just reluctant to hack apart the current exhaust without knowing a hundred percent sure that that's the right thing.
     
    #1 Sina Drums fan, Sep 18, 2021
  2. mr_guy_mann

    mr_guy_mann Senior Member

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    I'm not sure that I understand your question. You have been ignoring a problem with your car (upstream air fuel sensor) that likely hastened the demise of the cat. Replacing the sensor(s) has restored the ECM's ability to control fuel trim and monitor cat function. Now it detects a cat problem (P0420).
    IF there are no exhaust leaks at all from the cylinder head to at least 18" past the downstream O2 sensor AND the ECM has proper fuel control (both sensors can read full rich and lean correctly, and fuel trim numbers in data are 0 +/- 10%), no misfires, AND no TSB's for this fault; THEN the car needs a new cat.
    Assuming that all of the above is true then the original cat can no longer do its job and does you no good towards passing inspection. Have no idea if the replacement assembly outlet pipe would be long enough to prevent air reversion from skewing the downstream O2 readings. The idea of just hanging the cat and driving just baffles me (plus having the exhaust spewing out from under the center of the car don't seem like a great idea). If the light stayed off for a day or two then would you splice the rest of the system back on?
    Ain't no 100% sure anything- either your aftermarket cat keeps the light off long enough to pass or it don't.

    Posted via the PriusChat mobile app.
     
    #2 mr_guy_mann, Sep 18, 2021
  3. Sina Drums fan

    Sina Drums fan Junior Member

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    Thanks for the reply. I guess I didn't think it through where of course I have to drive it for it to cycle through before it would confirm if the codes are clear. I just wanted to avoid throwing parts at the problem. I would prefer to know for sure what's wrong before I fixed it. You're right nothing is 100%. I'm pretty sure it is the catalytic converter so I'll just go ahead and install it correctly and hope for the best, thanks.
     
    #3 Sina Drums fan, Sep 19, 2021
  4. Another

    Another Senior Member

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    I’m not sure if it applies here but regarding your comment about back pressure …
    I had a Toyota Supra that I took to the UK in the 1980’s. When I got there there was only leaded gasoline so I had the Toyota dealer remove the catalytic converter and they had a OEM spool piece that replaced it sized to keep the back-pressure the same as the catalytic converter. Car ran fine while I lived there, then shipped it back to USA and had Toyota in USA swap the spool piece for the catalytic converter that I had stored. Never had a problem with it. Sold it years later. One of the best cars I ever owned.
     
    #4 Another, Sep 20, 2021
  5. Sina Drums fan

    Sina Drums fan Junior Member

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    Finally installed the after market catalytic converter. Didn't break any bolts so it was a good day. Codes are clear so far. The exhaust donut was almost gone and must have been leaking so it is possible that was the cause of the code and I cut out a working cat. Live and learn.
     
    #5 Sina Drums fan, Dec 31, 2021
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    I have often found that the only donut gasket that works (ie, seals correctly) at the spring bolt joint is an OE gasket from Toyota. Even with aftermarket pipes the OE gasket seals the best.

    Posted via the PriusChat mobile app.
     
    #6 mr_guy_mann, Jan 1, 2022
    Pioneerscot likes this.
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