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Just had CEL come on. Error code P0420

Discussion in '1st Gen. Tacomas (1995-2004)' started by JT1521, Sep 17, 2018.

  1. Sep 17, 2018 at 10:58 AM
    #1
    JT1521

    JT1521 [OP] Well-Known Member

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    I just had my CEL come on. I checked it with my OBD scanner and code P0420 and P0420 P came up. Sighs. I don't have thousands of dollars to have my Catalytic Converter replaced. How do I find out for sure that is what needs to be replaced? Any thoughts on what to do? Can I just reset the code and see what happens? Will not replacing the Caty kill my engine? Thanks.
     
  2. Sep 17, 2018 at 11:03 AM
    #2
    Gunshot-6A

    Gunshot-6A Not a Fed

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    Could be an 02 sensor which is pretty cheap and easy to fix. May be an exhaust leak as well.

    Seems a few people have run a can of seafoam through, and that took care of the issue.
     
  3. Sep 17, 2018 at 11:32 AM
    #3
    JT1521

    JT1521 [OP] Well-Known Member

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    I have replaced both O2 sensors in the last 6 years or so. How do I know for sure if it is that before I change them and find out it is not that?
     
  4. Sep 17, 2018 at 1:48 PM
    #4
    onakat

    onakat Well-Known Member

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    catalytic converters don't go bad on their own. They are killed by rich fuel mixtures or contaminants (oil, silicon, coolant, etc). If you don't or didn't have any of these issues, your catalytic converter is probably fine

    If you want to make sure if you have bad O2 or catalytic, get (or borrow) a live data code reader to see the cat and o2 sensor output data. You'll see if they are behaving abnormally.

    It could be something as simple as a dirty MAF sensor, dirty o2 sensor or an exhaust leak
     
  5. Sep 18, 2018 at 12:15 AM
    #5
    JT1521

    JT1521 [OP] Well-Known Member

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    A live data code reader is different than my OBD II scanner?
     
  6. Sep 18, 2018 at 1:34 AM
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    DrZ

    DrZ Well-Known Member

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    Reset the code and see if it comes back. Sometimes it will stay off for thousands of miles before showing up again.

    Some (maybe most) OBD2 scanners have a function to allow you to see the live data (RPM, throttle position, O2 sensor voltage, fuel trims, coolant & air temperature, etc.) as the engine is running.
     
  7. Sep 18, 2018 at 5:03 AM
    #7
    onakat

    onakat Well-Known Member

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    some OBDII scanners have this function, some don't

    I would start with simple things first (clean the MAF sensor and throttle body while you're there) and then clear the code and see if it comes back
     
  8. Sep 18, 2018 at 5:46 AM
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    Blue92

    Blue92 Well-Known Member

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    Live data will chart the numbers while the vehicle is running. Most are upwards of $400 for a good one.
     
  9. Sep 18, 2018 at 6:30 AM
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    Wsidr1

    Wsidr1 Well-Known Member

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    @JT1521

    This unit is cheap and shows live data. You can download "Torque Engine Management and Diagnostics Tools" software (maybe $20, can't remember ("Torque Lite is free)) for your cellphone and see O2 sensor readouts. I have one and it has performed well on Toyota, Ford, and GM vehicles.

    https://www.amazon.com/gp/product/B005NLQAHS/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1
     
  10. Sep 18, 2018 at 8:54 AM
    #10
    wolfpackbd22

    wolfpackbd22 Well-Known Member

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    Mine was an exhaust leak right before the O2 sensor. Get under there and make sure there isn't a leak before replacing parts
     
  11. Sep 18, 2018 at 2:15 PM
    #11
    Bahmi

    Bahmi Active Member

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    For 70 bucks, you can buy a really good code reader made by

    SeekOne, got mine on Amazon. It's really,really good. 420 codes can be very deceiving.
     
  12. Sep 18, 2018 at 2:45 PM
    #12
    rzgkane

    rzgkane Well-Known Member

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    I agree with accessing the data before replacing parts. The P0420 in my 2000 2.7 was caused by a faulty bank 1 sensor 1 air/fuel rate sensor. The data showed it frozen at one voltage instead of vacillating like it's supposed to.
     
    Last edited: Sep 18, 2018
  13. Sep 23, 2018 at 6:26 AM
    #13
    JT1521

    JT1521 [OP] Well-Known Member

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    Ok I bought one of these. Will it tell me if one or both O2 sensors is the problem? What exactly am I looking for to see what may be the cause of the P0420 code with this live data diagnostics unit? Thanks.
     
  14. Sep 23, 2018 at 10:54 AM
    #14
    onakat

    onakat Well-Known Member

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    https://www.youtube.com/watch?v=9VZ5K8n5jj0

    he explains what data you want to see and what data you do not want to see
     
  15. Sep 25, 2018 at 11:18 AM
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    JT1521

    JT1521 [OP] Well-Known Member

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    Ok I am no expert on vehicles. I just ran the Torque Pro app and tested the O2 sensors. Here is the data it shows. Notice no data for the Bank 1 sensor 1. I am either gonna be stupid in saying this or not. lol Does the no data for the Bank 1 Sensor 1 upstream sensor mean its bad or bad wiring and that is the reason for the P0420 code? Here is the data:

    Screenshot_20180925-131704.jpg Screenshot_20180925-135321.jpg Screenshot_20180925-135300.jpg
     
    Last edited: Sep 26, 2018
  16. Sep 26, 2018 at 6:46 AM
    #16
    JT1521

    JT1521 [OP] Well-Known Member

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    Anyone know what to make of that?
     
  17. Sep 27, 2018 at 11:08 AM
    #17
    JT1521

    JT1521 [OP] Well-Known Member

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    Would be nice to hear anyone's opinion.
     
  18. Sep 27, 2018 at 12:05 PM
    #18
    onakat

    onakat Well-Known Member

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    Before concluding o2 sensor is or cat is bad, have you tried cleaning your MAF sensor and throttle body, or replacing sparkplugs (if it's been a long time since they were last replaced)? Common causes of p0420, with exhaust leaks. Do that, clear the code and see if it comes back

    And to answer your question, how long did you let the truck run? To diagnose properly, you need to have the exhaust reach it's normal operating temperature (a few hundred degrees). Sometimes you won't see output data until the sensor or cats have reached operating temperature.
     
  19. Sep 28, 2018 at 10:49 AM
    #19
    JT1521

    JT1521 [OP] Well-Known Member

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    I just drove for 15 minutes and then plugged in the BAFX Bluetooth diagnosis plug and it still is not giving me any data for the O2 bank 1 sensor 1. It shows bank 1 sensor 2 data. Can I unplug the bank 1 sensor 1 and check voltage with a digital meter and determine if it's bad? Thanks
     
  20. Sep 28, 2018 at 2:22 PM
    #20
    onakat

    onakat Well-Known Member

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    I see now... if you have a 2000 and later truck, you have an air/fuel sensor (wide-range o2 sensor) as the upstream sensor instead of a regular oxygen sensor. I believe it does show up as the blueish line (o2 sensor 1 wide range voltage).

    Usually, upstream sensor readings will fluctuate while downstream sensor will be fairly steady.

    yes, you can test oxygen sensors with a voltmeter. The two black wires are the heater element, blue wire is signal + and white is -
    https://www.youtube.com/watch?v=DvKZ2GDYEz4

    though, if sensor was bad, you would normally get a specific error code for it
     

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