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Uh oh! P0420

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Dat Boi, Oct 16, 2016.

  1. Dat Boi

    Dat Boi Junior Member

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    I was driving home tonight, and what do you know, the check engine light came on (y)

    Upon seeing the light pop on, I immediately pulled over and pulled out my handy dandy Bosch OBD scanner

    P0420!

    I have 293k miles on stock everything. From what I've read, it'll either be an 02 Sensor or a Cat.

    My plans for tomorrow: Check the temps of the cats with my thermal temp scanner.

    If the cats show up good with appropriate temps, I am guessing it'll be an 02 sensor?

    Anyone in the past have this issue?

    Thanks in advanced!
     
  2. JC91006

    JC91006 Senior Member

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    Most likely a cat problem. You can find good aftermarket cat on Amazon for$100
     
  3. Dat Boi

    Dat Boi Junior Member

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    Awesome. Maybe that would explain why I get that surging sensation. It started doing that a few months back, I am sure you recall my thread about that.
     
  4. JC91006

    JC91006 Senior Member

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    I read so many threads here, I can't remember them all lol
     
  5. Dat Boi

    Dat Boi Junior Member

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    Lol, I understand that!

    How do those aftermarket cats hold up from Amazon?

    I drive 50k+ miles a year, so I am worried about quality as well. Have you personally used one?

    I won't have lift access until Tuesday due to my busy schedule, but I plan on having this fixed by next week :)
     
  6. JC91006

    JC91006 Senior Member

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    This is a weld on unit, I've used it with great success. Replace the cat that's closest to the engine

    Magnaflow 99205HM Universal Catalytic Converter (Non CARB compliant)
     
  7. Dat Boi

    Dat Boi Junior Member

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    Okay cool!

    This will be a relatively inexpensive fix. My car is my business, so I want to take care of it :)

    I'll be doing the diagnostic work first thing Tuesday. I don't like throwing parts at things not knowing the issues lol.
     
  8. Dat Boi

    Dat Boi Junior Member

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    Update:

    I've noticed that the car feels sluggish. MPGs are down to low 40s, lol.

    Perhaps the rattling noise i've had is the cat?

    Diagnostics time tonight! I'll keep you guys posted on my findings
     
    bisco likes this.
  9. Dat Boi

    Dat Boi Junior Member

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    Update:

    Cat is in good working order

    However, I feel like the 02 sensors are a bit off.

    One is to spec, .5

    The other one hovers around 4 to 4.5 with sluggish response
     
  10. CooCooCaChoo

    CooCooCaChoo Active Member

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    If it is the cat, be thankful that you don't live in California. You should take the O2 sensors off and bench test them first. I hear one of them is a PITA to remove though.
     
  11. Dat Boi

    Dat Boi Junior Member

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    yeah, the cat is fine! All the temps are where they should be, which shows it's working normally :)

    Yeah, lol. I saw.

    Would a dirty MAF cause the same issues?
     
  12. CooCooCaChoo

    CooCooCaChoo Active Member

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    Only takes like 5 minutes to take the MAF off and clean it. I would give it a shot. Just don't touch the wires inside the unit. Otherwise it will be O2 sensors.
     
  13. Irishamerican2017

    Irishamerican2017 New Member

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    sorry I know this thread is old but I have a P0420 check engine code on my 08 prius with 208000 miles. I changed the downstream O2 sensor because the cords where cut and exposed. I also changed out the spark plugs and PCV valve and mass air flow sensor and air filter but I'm still getting the check engine light. So I went into the prius's diagnostic LAN code checked on the car itself and cleared the code and memory to see if that would help. now the check engine light comes on with the same code when read with a OBS2 but the cars code check system when done on the display shows no error.
     
  14. exstudent

    exstudent Senior Member

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    STOP posting everywhere.

    LAN function from the MFD (Multi Function Display) is for Navigation and Audio, diagnostic purposes.
    Emissions has nothing to do with Navigation and Audio.

    You still need to perform a proper repair. Until this is done, there will always be a code.

    You will most likely have to replace the Catalytic Converter.
    The upstream and downstream sensors have a specific test that could have been performed to see if replacement is needed. You needlessly replaced a sensor.
     
  15. Irishamerican2017

    Irishamerican2017 New Member

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    Exstudent I only posted to two of this forums so its not everywhere. second I didn't replace the sensor for no reason the sensor wires where cut and exposed so they needed to be replaced. and every mechanic I have talked to has told me that sensors only last 70,000 miles and my car has 208000 so they need to be replaced. and the LAN is not just for the radio and navigation by the way it gave me the P0420 code when it first came on the first screen is audio and navigation correct but the LAN button takes you to the check engine codes. my friend has a mechanic computer that can scan anything cost him like $20,000 and it said the sensor was bad as well. but now its still showing the check engine light but only after like 80 to 100 miles if it was a bad cat it would come on right away.
     
  16. Figster10

    Figster10 Member

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    Do you know if this can be bought in california and shipped in california? I keep receiving messages when trying to buy this on amazon about how it can't be picked up or shipped to a pick up hub
     
  17. eternalphoenix64

    eternalphoenix64 Junior Member

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    Mods, don't approve this one, I didn't realize it was an old, dredged up post initially.


    I went the same route. My MIL came on with P0420 and went away intermittently. Tried watching live data with code reader and couldn't determine for sure if it was O2 or cat, but I was guessing cat, but O2 sensor was cheaper to start with.

    Got a.... I think Bosch... O2 sensor from Amazon for something like $40, put it in, MIL on constantly then. Was gonna get the kit from Amazon that was around $235 (+tax) that bolts in from manifold to muffler, but found a shop in my area that would do a weld-in for $300 flat out the door, so I went that route. MIL gone.

    Until now, having new problems, but that's a post still awaiting mod approval
     
  18. JC91006

    JC91006 Senior Member

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    I actually have a spare one if you want to buy it. I haven't had the need to use it.

    When I bought mine, I shipped it to an address in NV, where I often visit.
     
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  19. Figster10

    Figster10 Member

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    Yes, where are you located?
     
  20. JC91006

    JC91006 Senior Member

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    I'm in southern california, near Los Angeles. If you're up north, I would just put it in the mail for you.
     
    Figster10 likes this.