P0420 code and 02 sensors question:

Discussion in 'KJ General Discussion' started by CWBenjamin, Mar 17, 2020.

  1. CWBenjamin

    CWBenjamin Full Access Member

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    I know there is a guy on here that will try to refute this, and I would love his input as well.

    What I want to know is if there is anyone on here that has, for certain, had a P0420 code on a jeep liberty, (bank 1 to be specific) and replaced an 02 sensor, and have it fixed the problem and clear the code?

    I see countless search results online that say it could be a downstream 02 sensor, but I can't find a good and easy way to test the 02 sensor. They all say pull it out and spend more time with all these weird tests than it is worth to avoid buying a new one.

    Thanks in advance and all advice is greatly appreciated!

    Second question, if I do need to replace my catalytic converter, what would be a good option under 250 dollars that can bolt right on without welding or cutting or doing any custom work?
     
  2. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

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    What year & How many miles on your Jeep?
    Start with the 02 sensors.
    [​IMG]
    See the following:
    https://www.700r4transmissionhq.com/p0420-jeep-liberty/
    Members here have used Walker cats with good success.
    That being said the OEM cats do last a long time, yet are very expensive.
     
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  3. tommudd

    tommudd Moderator Staff Member Moderator

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    I've replaced many of them Bank one and two, upstream / downstream etc with good results over the years
    why do you think someone is going to refute this ?
    Confused
    As far as cats go, none bolt right in without any mods to the exhaust
    Plus if you go cheap , the cheap ones do not flow as well as stock ones do
     
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  4. CWBenjamin

    CWBenjamin Full Access Member

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    It is a 2003 3.7L with 135k miles. Thank you for your suggestions I will look into this!
     
  5. CWBenjamin

    CWBenjamin Full Access Member

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    There is a guy on there that seems to be pretty intelligent when it comes to these jeeps that says that the 02 sensor has to be working in order for a p0420 code to show up.
     
  6. CWBenjamin

    CWBenjamin Full Access Member

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    I would like to add that I have noticed an occasional drop in rpm at stop lights, not a lot but noticeable and intermittent. Also, when I am driving at normal steady speeds I can feel an occasional tug from the engine as if I went over a small crack in the road or something... Just barely noticeable.
     
  7. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

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    Take a look at the rpm gauge and see if it is reading steady or drops a bit at the light.
    Idle issues can relate to the Iac, intake air control and cleaning the iac and port may help.
    I've replaced both the iac and throttle position sensor.
    The tps was replaced when I experienced flat spots in throttle at 1600 to 1700 rpm.
    You should still at first deal with the 02 sensors.
    Part of a tune up should also include new ngk spark plugs every 30 k miles.
    See the underhood sticker or owners manual for oem plugs.
     
  8. CWBenjamin

    CWBenjamin Full Access Member

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    Just did the plugs, also replaced throttle position sensor, intake seems fine, I even blasted some seafoam in the intake and have been running lucas through my fuel system.
    The rpms do a slight drop at stoplights after idling for a moment. not every time but frequent enough.
     
  9. KJGremlin

    KJGremlin New Member

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    I too have had a similar issue with my 02 KJ with the same P0420 code appearing. I replaced the downstream O2 sensor on the driver side and the CEL went off for about a month and then came back on. My spark plugs were done about a year and a half ago, I’ve cleaned the IAC as well. Another issue that I have is if I let off the throttle and coast toward a red light or just to slow down a little, when I go back to the throttle my jeep kind of sputters for a second before actually starting to accelerate again. I’m hoping it’s not a catalytic converter issue but that’s the only other thing I can think of.