Cat going bad?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by 12mpg, Sep 20, 2025.

  1. 12mpg

    12mpg Junior Member

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    Hoping to get some opinions on my 2014 Prius.
    I think my cat might be going bad and also noticing an increase in fuel consumption.
    This car has never thrown a code.

    Lately, I’ve noticed the exhaust sounds a little louder. (Not as loud as a cat being removed, but like, exhaust leak louder).
    I’ve also noticed some liquid dripping from my exhaust when running.
    The liquid also sounds like it’s pooling in the exhaust as I can hear a gurgling in exhaust while running.
    I’ve also noticed a strong chemical smell coming from my exhaust when running.
    I have been driving the piss out of this car the past 6 months and have been using it for car camping a lot.
    Not sure if the exhaust was always this loud and I’m just noticing it because I’m spending a lot more time in and around my car lately.
    Could be an exhaust leak but with that strong chemical smell coming straight out the tip of the exhaust, plus the increase in fuel consumption, I’m thinking the cat isn’t doing it job like it used to.
     
  2. PriusCamper

    PriusCamper Senior Member

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    When your cat clogs the bolts that connect the exhaust manifold and the cat together are on springs to protect from the movement of exhaust system on rough roads. So these springs will also make room for an exhaust leak when there's too much back pressure from a clogged cat. So if you smell a 1970's pre catalytic converter exhaust smell near the firewall in the engine compartment your flange gasket has failed and it's definitely a clogged cat. There's lots of cat soak recipes online to clean them, but when I learned all this it turned out being a waste of time.
     
    #2 PriusCamper, Sep 20, 2025
    Last edited: Sep 21, 2025
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  3. ASRDogman

    ASRDogman Senior Member

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    Perhaps the exhaust is rusting out, you should lift it up and inspect it...
     
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  4. bisco

    bisco cookie crumbler

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    how many miles on her?
     
  5. mjoo

    mjoo Senior Member

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    Those could be symptoms of a leaking head gasket. How's the coolant level?

    How's long term and short term fuel trims? Could indicate a sluggish or bad O2 sensor.

    SM-A536V ?
     
  6. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    Any signs of the Prius Death Rattle?
    +1 on the engine coolant level - that's usually the first 'tell.'
     
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  7. 12mpg

    12mpg Junior Member

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    I had to look this up but yes, I’ve been having this rattle intermittently a year or two prior.
    Tried looking into this noise before but couldn’t find the right words to describe what I was hearing.
    Thank you
     
    #7 12mpg, Oct 5, 2025 at 2:56 PM
    Last edited by a moderator: Oct 5, 2025 at 11:31 PM
  8. ASRDogman

    ASRDogman Senior Member

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    Any update???
     
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  9. 12mpg

    12mpg Junior Member

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    I forgot I even made this post until today. But I just learned about the notorious Prius death rattle. I’ve definitely had this issue since I bought the car 6 years ago. It hardly happened the first few years of owning the car. But has been getting progressively worse, especially the past two years.
    My only glimmer of hope is that my coolant level has remained unchanged, so it’s possibly just a clogged egr inlet manifold, or a bad egr valve.
    I just started researching this death rattle today so I will have to see what I can come up with. I might just start throwing some parts at it: spark plugs, coil pack, egr valve (depending on price), and see if that fixes things before I do a head gasket change.
     
  10. 12mpg

    12mpg Junior Member

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    New development:
    I think between the engine noise, gurgling(water) in the exhaust, and the misfire (death rattle), this issue has to be a head gasket.
    Further evidence points to this because my coolant level never moved in the past… until recently I noticed it go down quite a bit (now it sits at the low setting). So that coolant must be going into my cylinder causing the misfires, and then the coolant made its way into the exhaust.
     
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  11. Mendel Leisk

    Mendel Leisk MMX GEN III

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    ^ Yeah skip that, just a fool’s mission. Do clean the EGR system thoroughly as well as dealing with head gasket. Presumably never cleaned?

    I drone on about cleaning EGR at least every 50k miles; your head gasket failure at 75k is cold comfort.

    see my signature for info, last link is full engine section from repair manual.

    (On a phone turn it landscape to see signatures)
     
  12. bisco

    bisco cookie crumbler

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    75k is too early, is it possible they rolled back the odometer?