Upstream vs downstream O2 sensors

Discussion in 'KJ General Discussion' started by Cmf333, Jul 31, 2020.

  1. Cmf333

    Cmf333 New Member

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    Hi guys, I've been lurking on this forum for a little while but this is my first time posting! I recently got a 2005 3.7l Liberty. I've done some light maintenance on it and the O2 sensors are next on my list. I've seen some mentions that the upstream and downstream sensor are the same part on this particular engine but I wanted to confirm that before ordering. Can I order 4 of the same sensors for this vehicle or do I need to order 2 upstream and 2 downstream? Thanks!
     
  2. Big Al

    Big Al Let's get Cracken

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    Welcome to the forum, I'm new here to and would like to know too.
    I have a few codes that popped up and my mechanic says change the catalytic converter out. It also might be the O2 sensors I heard too.
     
  3. 03GoingStrong

    03GoingStrong Full Access Member

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    Never had to change one yet, but looked up the parts for my 2003 3.7L. The sensors have four different individual part numbers. Don't know what the difference is but if the illustration is accurate, the attached wiring harnesses are different lengths for one thing. Don't know if the part numbers are the same for an 05 but wouldn't be shocked if they are the same. Maybe someone will chime in.


    [​IMG]
     
  4. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

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    The Jeep is very picky re 02 sensors and when codes are present ensure you know which one is what.
    Only use Mopar or NGK/NTK 02 sensors period.
     
  5. tommudd

    tommudd Moderator Staff Member Moderator

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    ^^^^^^^^^^^^^^^ so true
     
  6. Big Al

    Big Al Let's get Cracken

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    Anyone know if we can test these before replacing them all.
    Sounds like I have fire the parts cannon to get rid of my "mil" light that is on.
    Sounds like I have to fire the parts cannon at the Liberty to get rid of these codes.
    P0420
    P0442
    P0445
     
  7. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

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    Big Al, Here is what those codes mean. Your codes are not related to any 02 sensors..
    P0420 1/1 Catalytic Converter Efficiency.
    P0442 Evap Leak Monitor Medium (0.040) Leak Detected.
    P0445 is the OBD-II generic code for a fault involving the purge control valve along the evaporative emission control system.
    The evaporative emission control system involves the fuel cap, gas tank, charcoal canister, and the purge control valve.
     
  8. 03GoingStrong

    03GoingStrong Full Access Member

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    LibertyTC provided the breakdown for the codes. Thing is, when I've had the rare fault code and it was related to the emission system, I've found a busted rubber emission or vacuum line somewhere ... replaced rubber hose piece, cleared codes and problem corrected. Not saying you have failed rubber line(s) but I'd check the simple stuff before going off on a tangent or throwing parts at it.

    The first rubber lines to go on my 2003 KJ Sport were two short pieces of rubber hose right up against the firewall, behind the driver side valve cover and were hard to see unless looking right at them. Another time, there was a failed rubber hose piece I had to crawl under the Jeep to find. Can't remember exactly, but it was near the transmission or transfer case and joined two small diameter metal pipes together as the line went to the rear of the Jeep. There should be a vacuum line sticker and emission line sticker drawing under the hood. Just follow the lines whether metal or rubber. The metal lines have short rubber pieces here and there.

    If you do find failed rubber lines, no need to buy Mopar replacements. Just go to any parts house and they'll cut the needed lengths off spools of rubber hose as needed.
     
    Last edited: Aug 1, 2020
  9. Cmf333

    Cmf333 New Member

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    Thanks for the feedback, only one of my sensors is returning high voltage, but the car is at 140k so I'm going to replace all 4.