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P0420- Cat is dead, need a plan of action

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by MisterMilox01, Aug 12, 2023.

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  1. MisterMilox01

    MisterMilox01 New Member

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    Hi all,
    I’ve been troubleshooting (I mean, sitting on) a problem with my cat for awhile now. I’m running a ‘07 Prius with 300k miles on the original engine. I’ve had a check engine for awhile now, ran Techstream and discovered it was the P0420 code but decided to sit on it as running CataClean and seafoam only made the issue disappear temporarily. I know that due to the amount of miles on my engine, it’s begun burning oil more than it should, making this issue worse, and sure enough I lost acceleration on the highway today, giving me the triangle of death.
    (Mid post update, I just grabbed my computer to run Techstream again to check my DTC’s, and it’s gone now? I’m so confused at this point.)
    I got to about 45 MPH, felt the car hitting high RPM’s but I wasn’t getting any acceleration, it kinda ‘kicked’ (which is something it’s been doing when city driving recently as well) and I lost all power and got the triangle of death. I believe this is due to the substrate getting caught in the way of the exhaust (I have a loud rattling sound that can often be heard as well) and back pressure causing the engine to shut down, prompting the triangle of death. The car is still driveable and all signs point to the cat being the problematic party. Any ideas for the best way to go about this?

    Can I drive the car temporarily without having the cat/exhaust attached to the engine? Should I temporarily cut out the cat until a replacement is ordered? And does anyone have recommendations for non-OEM cats to buy? Simply because I have 300k miles, I’ve been looking at a $100 one on Amazon as it’s cheap and I know spending much money on this is stupid if I don’t have the oil burning issue resolved too.
     
    #1 MisterMilox01, Aug 12, 2023
  2. mr_guy_mann

    mr_guy_mann Senior Member

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    You should get a capable scantool and see what codes triggered the "master caution" light (RTOD). Most scantools can't check all systems on a Gen2 Prius. Here's a thread that reviews several scantool apps and devices.

    https://priuschat.com/index.php?posts/3290690

    Yes, a broken up cat can restrict the exhaust and cause reduced power. That usually only happens if the engine has been misfiring, which sends loads of unburnt air and fuel into the cat- causing it to overheat and fail.

    A misfire on a Prius makes a rattle sound as the uneven engine operation "beats up" on the spring loaded damper that connects the ICE to the transmission.

    Yes, you have a deficient cat causing a P0420, but without more information and testing, it's just a guess as to what's causing your other problems.

    Sometimes guessing works, other times it just costs (wastes) time and money.

    Posted via the PriusChat mobile app.
     
    #2 mr_guy_mann, Aug 13, 2023
  3. rjparker

    rjparker Tu Humilde Sirviente

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    If you do buy a new cat I would get one that will clear your check engine light by actually working. This unit does that and fits nicely.

    IMG_2572.jpeg

    Napa and other autosupplies may have them in stock.

    Plus you could join the underworld and sell your oem cat for several hundred dollars. Maybe in Wentzville selling cats is above board like in Texas.
     
    #3 rjparker, Aug 13, 2023
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  4. MisterMilox01

    MisterMilox01 New Member

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    Interesting. I’ve never heard that that rattle could be a misfire, only the thought it was the substrate that had come loose.

    On your note regarding scan tools- is Techstream not a capable scan tool? Afaik, thst program is the crème of the crop for checking ECU’s on a Prius. Am I misinformed?

    If I am misinformed, then absolutely I agree that gathering more info to solve this issue better is worth it. I was just under the impression that Techstream met that caliber of quality for troubleshooting.
     
    #4 MisterMilox01, Aug 13, 2023
  5. MisterMilox01

    MisterMilox01 New Member

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    haha St. Louis definitely has a market for Prius cats, that’s for sure.
    As for the product you suggested, that looks much more reliable than what I was lookin at! Thank you, I’ll look into this a little further.
     
    #5 MisterMilox01, Aug 13, 2023
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    I missed the "mid point update" in the first post. If there was a fault that triggered the master caution light (unless it was low engine oil pressure or some-such), then it "should" have set a code that Techstream code read (at least a history code).

    I have seldom heard a (broken up) cat rattle when operating the car. I only hear it when smacking the exhaust system at the cat with a hammer or wood block.

    You can watch misfire counters in ECM data on Techstream while (someone else) is driving the car. If you see any counters increase while hearing the rattle, that would suggest that you do actually have misfires (most often the result of bad spark plugs and/or ignition coils).

    Posted via the PriusChat mobile app.
     
    #6 mr_guy_mann, Aug 15, 2023
    Last edited: Aug 15, 2023
  7. MisterMilox01

    MisterMilox01 New Member

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    I’ve noticed on Rock Auto specifically that there is a section for OEM and for Aftermarket cats for my year Prius. Any recommendation as to which one I should consider of higher quality? They’re similarly priced, which is why I ask.
     
    #7 MisterMilox01, Aug 16, 2023
  8. TMR-JWAP

    TMR-JWAP Senior Member

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    I've used this model in a couple dozen Gen 2s. I also typically install a new downstream O2 sensor (reasonably priced DENSO from RockAuto about $55) The cat was typically costing around $130, but prices have dropped. I bought a couple more just about a month ago.

    Catalytic Converter 2004-2006 2007 2008 2009 for Toyota Prius 1.5L Front | eBay

    When I first started buying aftermarket cats, I tried several different ones. This is the only model that comes with the correct fasteners and a decent donut gasket. The end of the pipe is necked down to be an extremely good fit over the OEM pipe. Unfortunately, the clamp supplied with the kit fits the "un-necked-down pipe", so I purchase Heavy Duty 1 3/4" clamps from O'Rielly's Auto Parts and they work fantastic.
     
    #8 TMR-JWAP, Aug 16, 2023
  9. MisterMilox01

    MisterMilox01 New Member

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    Thanks for the recommendation! I’ll definitely be looking at that O2 sensor.

    does this one guaranteed clear the codes as well? That’s what I’m most curious about with these aftermarket cats.
     
    #9 MisterMilox01, Aug 16, 2023
  10. TMR-JWAP

    TMR-JWAP Senior Member

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    I have used dozens of them and have no problems with codes.
     
    #10 TMR-JWAP, Aug 16, 2023
    Pioneerscot and MisterMilox01 like this.
  11. Pioneerscot

    Pioneerscot Junior Member

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    I really appreciate the good stuff found on this sight. I just ordered this 75 dollar cat and will get rid of needing to run the 02 sensor extender, the extensor has been working, but my thoughts are that the air fuel mix might be altered enough to cause damage, car has 230k and runs great currently. Bought the car for a thousand bucks, it needed a traction battery and a coolant storage tank to get it up and running and a few cosmetic trinkets over 8k miles later it runs great
     
    #11 Pioneerscot, Sep 7, 2024
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