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P0141 CEL still on after replacing O2 Sensor

Discussion in '1st Gen. Tacomas (1995-2004)' started by Sodom, May 18, 2019.

  1. May 18, 2019 at 12:21 PM
    #1
    Sodom

    Sodom [OP] Well-Known Member

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    My '01 V6 came up with a P0141 code after sitting for a month. I replaced bank 1 sensor 2 with a Denso one and I still have the same code. I have tried clearing multiple times.

    The code is specifically for the O2 sensor heater circuit.
    When the truck is on, I get battery voltage at both heater wires and no sensor readings. I have been checking for continuity/shorts and I am having a difficult time locating the problem.
    I checked both the new and old sensors for heater element resistance, and they are both in spec (so I think it seems to definitely be electrical related).

    Does anybody have any advice for me? Thanks
     
  2. May 19, 2019 at 2:43 AM
    #2
    cruiserguy

    cruiserguy Well-Known Member

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    So you've definitely done the correct testing so far. So if the heating element in the sensor tests good, then the short or open must be in the wiring between the sensor and the ECU.
     
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  3. May 19, 2019 at 3:58 AM
    #3
    Wyoming09

    Wyoming09 Well-Known Member

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    Is it possible your ECU got really wet or saw a Voltage spike ??

    It is part of the whole circuit .

    One can`t rule out Evil Rodents chewing on things
     
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  4. May 19, 2019 at 11:51 AM
    #4
    Sodom

    Sodom [OP] Well-Known Member

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    I don't think it could have got wet or saw a voltage spike.
    The truck did sit for 5 weeks, so the evil rodent theory is definitely plausible.

    I did check continuity between the sensor and ECU and it looks all good though. And I don't have any other check engine fault codes.
     
  5. May 19, 2019 at 12:07 PM
    #5
    cruiserguy

    cruiserguy Well-Known Member

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    Well if continuity is good on wires from ECU to the sensor, the only thing possible is bad sensor or bad ECU right? I don't think there is anything else in the circuit??? Weird. Maybe you got a bad sensor? Can you see if the sensor is communicating to the ECU? Like with an OBD2 reader or something?
     
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  6. May 19, 2019 at 1:41 PM
    #6
    License2Ill

    License2Ill Woke like a Coma Toyota Tacoma

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    It's a dry heat thou, AZ
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    Bailing wire & Duct tape
    If an 01 is anything like my 04, critter damage is unlikely because all wiring from the B1S2's connector to the ECU is all within the cab entering under the Pass. front seat.
    I agree with the above comments. I'd try another sensor to start. We get brand new- fresh out of the package equipment failure all the time at work...


    Also is Sensor 2 transmission dependant like sensor 1 is? As in, two different sensors available for the same year truck depending on if the truck has either a manual or automatic transmission? I know that's the case for Bank 1 Sensor 1...
     
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  7. May 19, 2019 at 4:38 PM
    #7
    Sodom

    Sodom [OP] Well-Known Member

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    Yeah, I went for a drive yesterday and the sensor was reading 0V for a while and then read only a max of about .1 to .15 volts which obviously is not normal. This had me confused, but I though the sensor is supposed to read normally once up to temp from the heat of exhaust, even if the heater circuit is not working.

    But then again, the code is just for the heater circuit. Seeming like the ECU is malfunctioning for just this thing.

    The resistance on the new sensor is in spec. Since the heater element is essentially just a resistor, I feel like there shouldn't be much that could go wrong. But I guess I should try another one.
    I used Denso part # 234-4189, which according to Denso is the OE style sensor for an '01 V6.
     
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  8. May 19, 2019 at 4:46 PM
    #8
    eon_blue

    eon_blue Unknown Member

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    Make sure the sensor was installed correctly and the gasket was seated well, any leak there can trip a faulty sensor code.

    I had this same issue but with the rear o2 sensor p0136, replaced the sensor and all was well. If its sealed well then I'd try another new Denso sensor before digging deeper into the wiring or the ECU
     
  9. May 19, 2019 at 4:52 PM
    #9
    Sodom

    Sodom [OP] Well-Known Member

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    I checked for leaks and could not feel any. I don't think leaks would cause a p0141 code though because the code is just for the heater circuit.


    Yeah, I think I am going to try another Denso sensor first and then go from there.
     
  10. May 19, 2019 at 4:58 PM
    #10
    Bishop84

    Bishop84 Well-Known Member

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    In the trade, heater circuits are almost 99% the sensor, very very rare it's anything else.

    I would measure voltage to pin #1 and #2 (red white and white red) when the key is turned on. See what kind of voltage is there, this would be faster than checking for continuity of the circuit.
     
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  11. May 20, 2019 at 2:25 AM
    #11
    Sodom

    Sodom [OP] Well-Known Member

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    Yes, I did measure R-W to W-R with the sensor plugged in and got 0V and battery voltage on both to ground.
     
  12. May 20, 2019 at 10:00 AM
    #12
    Glamisman

    Glamisman Well-Known Member

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    NEW = Never Ever Worked.
     
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  13. May 21, 2019 at 3:23 PM
    #13
    Sodom

    Sodom [OP] Well-Known Member

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    New sensor did not work either.
     
  14. May 21, 2019 at 7:08 PM
    #14
    Glamisman

    Glamisman Well-Known Member

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    Just verifying that we are talking about the same thing. B1S1 is the A/F sensor and B1S2 is the O2 sensor, the one after the catalytic convertor. Your code is for B1S2.

    IIRC, at 68 F the resistance should be 11 to 16 ohms. The PCM is looking for this resistance cold and it should quickly rise to 23 to 32 ohms as the sensor heats up. If the PCM does not see a certain resistance in the circuit within a certain time, the CEL is illuminated. Check the resistance of the heater circuit first and if withing range plug it back in and turn the key on for a minute. Dont start the car. turn the key off and check the resistance again and compare. The next step would be to locate the heater circuit wires at the PCM. I dont have 2001 wiring diagram but I do for a 2000 which I uploaded. Disconnect the battery then locate and disconnect the correct plugs on the PCM and back probe the harness and check the resistance in the total circuit. The pins on the PCM connectors are easily bent so be careful reinstalling the plugs. While you are connected to the harness check for voltage and grounds... a decent test light hooked up to battery ground and battery positive should tell you if you have any issues. If after all of this, the resistances are where they are supposed to be then I would highly suspect an issue with the PCM.

    on a side note, URD makes a rear o2 sensor eliminator. I use it to solve a nagging P0420 issue on my Tacomas that are kept at my place in Cabo... bad mexican gas and all. It has been 3 years and there are zero issues. Not saying that you should throw this at it, it is just an option.
     

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  15. May 21, 2019 at 7:14 PM
    #15
    cruiserguy

    cruiserguy Well-Known Member

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    Wow
     
  16. May 22, 2019 at 4:16 PM
    #16
    Sodom

    Sodom [OP] Well-Known Member

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    I essentially did all of this, but I am going to do it again more thoroughly and record my findings and go from there. Thank you for this writeup, very helpful and thorough.

    If none of this works, anybody have any good info on replacing the ECM? Thank you
     
  17. May 22, 2019 at 10:11 PM
    #17
    Glamisman

    Glamisman Well-Known Member

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    damn, a head scratcher... just like it says in the factory manuals when you have done EVERYTHING... replace with know good unit. I HATE that. I think the PCM is plug and play, not 100% sure that the PCM has to be coded to your VIN or not. Something else I just thought about, when you got the sensor, did they go off the VIN or did you just ask for a sensor for a 01 Tacoma, V6 blah blah blah. Look at the emission sticker on the hood and see if your truck is a 49 state or a CA truck. This too simple of a thing to be this difficult.
     
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  18. May 23, 2019 at 12:15 AM
    #18
    Wyoming09

    Wyoming09 Well-Known Member

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    ECM match part numbers plug and play !!

    For What ever reason Denso Aftermarket lists # 234-9003 as the up stream AF sensor

    The downstream O2 sensor 234-4189

    You think Rodents can`t get into the cab they love the heater ducts .

    Really curious to see how this plays out as this seems to be the only code when my ECM failed there was like 5 codes
     
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  19. May 25, 2019 at 10:40 AM
    #19
    Sodom

    Sodom [OP] Well-Known Member

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    So, the O2 heater resistance is 13.8 ohm. Does not change with they key to ON because it does not actually warm up.

    I should then be measuring the resistance from the B+ (W-R) terminal on the ECM to the HTS terminal (R-W), obviously with the sensor plugged in, correct? I am getting 13.9 ohm, so that looks good.

    Going to check voltage and ground now....
     
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  20. May 25, 2019 at 11:10 AM
    #20
    cruiserguy

    cruiserguy Well-Known Member

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    Not getting voltage then right? If it passes ohms test then you shouldn't be getting voltage, unless of course it fails under load but I doubt that.
     

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