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Code P0420 BANK 1issues

Discussion in '1st Gen. Tacomas (1995-2004)' started by Milksteak4x4, Aug 1, 2020 at 8:07 AM.

  1. Aug 1, 2020 at 8:07 AM
    #1
    Milksteak4x4

    Milksteak4x4 [OP] New Member

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    Taco team!
    I have a 2001 Taco 3.4 V6. So, due to budget restrictions I bought an upstream Denso replacement o2 sensor. First mistake I know (should have bought BOSCH and replaced upstream and down stream). I replaced the upstream sensor (with the denso) and the light came back on. I am putting 87 octane or better in the tank so I don’t believe that is the issue. Ive checked for leaks on the Cad converter/muffler and I cant feel anything, although the Gaskets look pretty shot. The truck is running fine should I let it be? I am on a budget so what should my next move be?????
    Say screw it till something else goes wrong??
    Change both O2 Sensors for Bosch?
    Change cad converter?
    BG Platinum 44k Fuel system cleaner? (Never sea foam I’m told)

    Thanks!
     
    Black DOG Lila likes this.
  2. Aug 1, 2020 at 8:34 AM
    #2
    Wyoming09

    Wyoming09 Well-Known Member

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    New Tripoli Pa
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    Super Springs
    Welcome !

    Did I miss something Since when have Bosch O2 sensors become the go to??

    Bosch Sensors most often cause more problems

    With the PO420 code the downstream sensor should be changed first.

    How many miles ?? It does not take much of a exhaust leak to trip that code.

    As the ECM is not seeing enough difference between the 2 sensors .

    It is your truck what ever option works best for you.
     
  3. Aug 1, 2020 at 8:36 AM
    #3
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    Virginia
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    2003 Tacoma SR5 2.7 5 speed 4WD
    Stock. EZ pass.Dump pass.Inspection sticker.Convict printed lic.plates.FG cap.
    Welcome aboard new member
    #1 Denso only from Denso.com or Toyota only.
    #2 Make sure B1S1 on your taco is A/F or O2 sensor. Emissions Sticker under hood say's California compliant=A/F sensor.
    #3 Upstream exhaust leak check including manifold.
    #4 Fuel does make a difference.Some filling stations Ethanol is over 10%
    Try Cataclean after a tank of ethanol free.
    #5 Muffler shop test catalytic converters
    What state do you live in?
     
    Milksteak4x4 [OP] and TRD493 like this.
  4. Aug 1, 2020 at 9:03 AM
    #4
    Milksteak4x4

    Milksteak4x4 [OP] New Member

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    Thanks for this I’m going to start working my way through the list. I live in CO. I was told Bosch is the way to go for 02 sensors is this wrong?
     
  5. Aug 1, 2020 at 9:10 AM
    #5
    Bishop84

    Bishop84 Well-Known Member

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    No to bosch on Toyotas, stick to denso, it's oem.

    If you only have P0420 its 99% a cat, its rarely a sensor. But start with the exhaust gaskets if you think they are worn and leaking.
     

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