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O2 Sensors don't match?

Discussion in '1st Gen. Tacomas (1995-2004)' started by AJColorado, Jan 2, 2017.

  1. Jan 2, 2017 at 6:20 PM
    #1
    AJColorado

    AJColorado [OP] Member

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    This is my first post here, so hello all!

    I have a 1999 Tacoma (3.4 v6, Manual 4x4 SR5) with the check engine light on, the previous owner had a diagnostic tool and told me it was the downstream O2 sensor. I want to replace both sensors, but when I looked up the part for my truck at Denso, the recommended part doesn't match what I'm seeing under the truck. Maybe I've got the names wrong but would appreciate your thoughts on this.

    Thanks!

    Denso says:

    part 234-4154 = Downstream
    part 234-4161 = Upstream

    The sensor in front of the cat. has the metal flange and two bolts, the one toward the back has no flange and looks more like a spark plug.

    Here are some pics:

    Both Sensors:
    both.jpg

    Rear
    close.jpg


    Front

    frontclose.jpg
     
  2. Jan 2, 2017 at 6:27 PM
    #2
    devinzz1

    devinzz1 Well-Known Member

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    Everything after front o2 isnt factory. You cant tell because everythings welded together instead of bolt on flanges.That isnt factory style downstream o2.
     
  3. Jan 2, 2017 at 6:31 PM
    #3
    AJColorado

    AJColorado [OP] Member

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    Okay thanks, I was starting to think that had to be it. The downstream one looks like a Tundra...

    So I guess that brings up another question will the O2 sensor that fits the custom exhaust work okay for the truck?
     
  4. Jan 2, 2017 at 6:56 PM
    #4
    devinzz1

    devinzz1 Well-Known Member

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    I know when looking for a sensor for my truck that there are more than one option from denso. One of them was a screw in style like what you need that came with an adapter plate. You could just use that without the adapter and still be sure itl work.
     
  5. Jan 2, 2017 at 7:15 PM
    #5
    AJColorado

    AJColorado [OP] Member

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    Okay, I had a look on Denso and all the 1st gen sensors have the bolted flange with no threads to screw it in. It looks like it was modified with a 2nd gen catalytic converter or at least the exhaust pipe, because the downstream sensor looks like the ones for a 2005. But I'm guessing that the 2005 sensor isn't going to work right because they only come for a 2.7L and 4.0L.

    I'm thinking I may have to weld some bolts on there to fit the right sensor. Or maybe I need to figure out what kind of catalytic converter it is and match the sensor to that?

    Update:
    The catalytic converter has been cut out and a new one welded in. It doesn't have the o2 sensor, that was cut and welded separately. It is a Walker N/TA/99400 - 17370 - 0613. Still need to get the o2 sensors right...
     
    Last edited: Jan 2, 2017
  6. Jan 2, 2017 at 7:43 PM
    #6
    cruxofthebisquit

    cruxofthebisquit Well-Known Member

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    Check that sensor and see if it's really bad. Those aftermarket cats fail too, Does scan tool say cat is 'ready'?
     
  7. Jan 2, 2017 at 7:44 PM
    #7
    AJColorado

    AJColorado [OP] Member

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    Sadly I don't have access to the scan tool anymore...
     
  8. Jan 3, 2017 at 1:50 PM
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    Caligula

    Caligula It's the COVFEFE

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    Unless you are getting a P0420 or P0136 code, no need to touch the rear o2. It is just an efficiency monitor.

    The front has two part numbers, one is a narrowband o2, the other is a wideband A/F sensor. 99-2000 was the transition period for this. There is also a California spec emissions package that has a wideband A/F.
     
  9. Jan 3, 2017 at 3:21 PM
    #9
    AJColorado

    AJColorado [OP] Member

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    Thanks, I'm not sure what the code is... but I was thinking to change it to get the check engine light to go off in case there was anything else.

    Caligula: Do you mean that I have a choice of two different sensors for the front?
     
  10. Jan 3, 2017 at 7:50 PM
    #10
    cruxofthebisquit

    cruxofthebisquit Well-Known Member

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    OME and worth every penny.
    no, Cal. emissions get one, 49 state gets the other. After 99 everybody uses Cal. emissions.
    We've kind of learned now that the '99 models are the trickiest years to diagnose what is going wrong because as stated, it's a transition year. The computer doesn't really recognize the problem as well as years later. That's the reason to test each part before replacing. You could waste a lot of money that way. Like the converter. It may have been bad and had to be replaced but maybe not.

    It's not just Tacomas. I have a '99 Sienna, my Sis has a '03. Same vehicle, same engine. The emissions are worlds apart and take readings much differently.
     
    Last edited: Jan 3, 2017
  11. Jan 3, 2017 at 9:48 PM
    #11
    DrZ

    DrZ Well-Known Member

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    To add to the confusion, sometimes Denso has a generic O2 sensor that you need to splice the old electrical connector to and another (more expensive one) that comes with the connector, each with a different part number, but in the parts catalog it will show both fitting.
     
  12. Jan 4, 2017 at 12:46 AM
    #12
    Caligula

    Caligula It's the COVFEFE

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    ^What he said.

    The 49 state and CA emission sensors look almost identical, but they are internally different and the plugs are different.
     
  13. Jan 4, 2017 at 10:16 AM
    #13
    Dirty Pool

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    99 V6 manual, built Feb 99, sold March 99 in MD. Build sheet has "50 state federal emissions requirement" listed in the optional equipment column.

    Upstream sensor was 89465-09240 with dealer vin# confirmation.
     
    Last edited: Jan 4, 2017
  14. Jan 5, 2017 at 11:27 AM
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    AJColorado

    AJColorado [OP] Member

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    Thanks for all the info. I just went ahead and ordered a scanner, for $20 seems like a good investment: BAFX Products 34t5 Bluetooth OBDII Scan Tool for Android Devices

    Ill update with the readings.

    It turns out the previous cat. converter was stolen and so this one is new as of 2013. They must have used a generic part for the pipe fitting. On closer look the cat. converter is welded on and the rear o2-sensor is in another small piece that is welded between the cat. and the original muffler. The cable on the rear sensor is obviously much longer than it needs to be, but does look like a plug-in variety rather than a spliced one.

    From what I've read the computer can be picky about non-stock o2 sensors.
     
  15. Jan 14, 2017 at 6:50 PM
    #15
    AJColorado

    AJColorado [OP] Member

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    So, the scan tool reports code: P0141 - 02 sensor heater circuit bank 1 sensor 2.

    My main remaining question is which part to use to replace this? Is there a generic part with threads that will work?
     
  16. Jan 15, 2017 at 3:09 AM
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    Caligula

    Caligula It's the COVFEFE

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    As a Californian, id say fuck it.
     
  17. Jan 15, 2017 at 4:01 AM
    #17
    NightProwler

    NightProwler Well-Known Member

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    In my case, I discovered my front was changed at some point and was not denso like the rear was. Looks like the one you have with just threads and no dual stud bung. I just put in a Bosch. So new Bosch up front and new denso in rear. No issues. Fwiw.
     
  18. Jan 19, 2017 at 1:00 AM
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    libagui

    libagui Well-Known Member

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  19. May 15, 2020 at 7:24 PM
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    awpldlto

    awpldlto Member

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    I bought the non Cali without realizing that my truck was Cali emissions and the front sensor is different and has a different plug. Can I just de-pin the Cali sensor and put the plug on the new sensor or will there be tuning issues?
     
  20. May 15, 2020 at 7:32 PM
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    Black DOG Lila

    Black DOG Lila Well-Known Member

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    Stock. EZ pass.Dump pass.Inspection sticker.Convict printed lic.plates.FG cap.
    If the plug is different you have the wrong replacement sensor.
     
    Wyoming09 likes this.
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