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Addressing some common misnomers of the P0420 code

Discussion in '1st Gen. Tacomas (1995-2004)' started by Caligula, Oct 20, 2015.

  1. Jul 24, 2017 at 1:27 PM
    #21
    thoth

    thoth Active Member

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    2002 Tacoma SR5 3.4L V6 PreRunner
    i got the sensors from Amazon.

    Upstream: https://smile.amazon.com/gp/product/B000C5WD2Q/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1
    Downstream: https://smile.amazon.com/gp/product/B000C5UFOY/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

    I sprayed the nuts on the sensors a day or two ahead of time with Liquid Wrench. The Front o2 sensor came off without issue. was CAKE. was done in 10 mins. The rear o2 was a pita since it had the heat shield still in place. I tried using my articulating socket wrench to get the nuts off but i thought i was rounding the nuts off so i destroyed the shield in order to get clear direct access to the nuts. WELL after i ruined the shield i realized i was not rounding the nuts at all... the nuts were just loosening up really easily! So had i just kept trying then it would have been SO much easier and id still have my heat shield. Once i got the shield off the rest was cake. The downstream o2 sensor does not come with a plug at the end of it. So you have to cut and splice the new sensor in using the original sensor's plug. Im electronically inclined so doing the splice was fun and easy. just remove the entire old sensor all the way up to the plug. Just unplug it from under the floor mat. Then you can easily splice the new sensor to the old plug on your work bench instead of under the truck.

    My advice would be to replace the rear sensor then the front if still not resolved. but im also a newb. I also recommend buying an OBDII bluetooth adapter from amazon, super cheap, then buying Torque Pro for your cell fone. Then you can do basic OBDII scantool diag. The rear o2 should show as a solid line with little variation when you hit the accelerator.
     
    Last edited: Jul 24, 2017
    Elwing and PROseur like this.
  2. Sep 28, 2017 at 11:37 AM
    #22
    20TACO00

    20TACO00 Member

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    repainted, powder coated stock rims, KISS
    Do these O2 sensors fit a 4x4? I have an 00 Tacoma SR5 extended cab 3.4L automatic. I replaced the cat last year and the CEL comes off and on after a few months of driving. P0420 code is the only code I'm getting. I'm thinking of just replacing both sensors while I'm under there. Thanks for any help.
     
  3. Jan 16, 2018 at 10:21 AM
    #23
    2ndToy

    2ndToy Well-Known Member

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    After 5 months of trying to fix this issue. I could see the volt reading. I could see how the readings responded. I could see how the 2nd sensor would drop below what it should. I tightened the exhaust up. Didn’t fix the issue. However on a cold day I observed a puddle of water under the truck. I could see small amount of water dripping a connection in the exhaust. Couldn’t hear any leaks. But when I put my had up there I could feel it sucking air. New gasket , problem solved. If it wasn’t for the moisture it was sucking in I don’t think I would of found the issue.
     
  4. Jan 24, 2018 at 2:46 PM
    #24
    x2468

    x2468 Well-Known Member

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    I've been dealing with a loss of MPG for a long time now... I used to get consistent 18mpg mixed and now it's more like 14-16. For a long time I had the p0420 code (bank 1). I think the longest I had it was a 3 months. Then it would go away come back. But now I haven't seen it in at least 6 months, but my MPG is still shit. I changed plugs and wires and cleaned the MAF and that didn't seem to fix anything. Anyone have any thoughts?
     
  5. Mar 3, 2018 at 9:07 AM
    #25
    srsupertrap

    srsupertrap Well-Known Member

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    2001 Tacoma SR5 V-6 TRD 4 X 4
    Bilstein 5100s, Borla 14945 S/S Exhaust, Fram Air Hog Filter, Diff Breather Mod & NGK Wires
    Thanks OP for sharing your expertise & insight.

    My 2001 Taco has 197K & runs excellent. After replacing both original O2 sensors with OEM Denso's over a year ago (185K), my Taco is now getting p0420 codes. From a troubleshooting standpoint what's the logical next step to eliminate the root cause? Should I be unbolting the Cat and performing a visual inspection to make a decision on buying a new Cat or other?
     
  6. Mar 3, 2018 at 10:59 AM
    #26
    2ndToy

    2ndToy Well-Known Member

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    I would feel around for leaks or use a small piece of hose/3/8s in size put it to your ear and put the other around the second O2 sensor and around the connection of the exhaust before sensor while the motor running. Read some of the post again. I saw fuel pump. Maybe it’s a gasket like mine. Cheaper things could be the cause.
     
  7. Jun 8, 2018 at 8:26 AM
    #27
    ThunderOne

    ThunderOne Average Contributor

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    1ST GEN OR GTFO
    PlastiDERP
    @tcBob please un-sticky. Too many stickies in the first gen section.
     
  8. Jun 9, 2018 at 8:29 AM
    #28
    ClevSix

    ClevSix Well-Known Member

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    Kings, AAL, 33s... more to come.
    Please don't unsticky this...
     
  9. Nov 12, 2018 at 7:03 PM
    #29
    Wunhunglo

    Wunhunglo Member

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    Okay here's my story. 02 dbl cab 3.4 152k Cel came on, said bank 1cat was stopped up. So just replaced rear cat(it was cheapest) cleared cel,15 miles down the road cel back on to late in the day to have code read. What next? Go have code checked again? Replace front cat as well? Replace 02 sensors? Bought truck for my son's first vehicle. Want it right. Please help mechanically inclined but need it in simple terms. Haha
     
  10. Nov 12, 2018 at 7:13 PM
    #30
    2ndToy

    2ndToy Well-Known Member

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    Mine came back because it didn’t seal at the front gasket of the 2nd cat which add more fresh air. You can use a small hose an check the connections. I had to use a gasket and grind it down to fit the small gaskets didn’t work. Try the cheaper items first. Clean throttle body. Use C foam.
     
  11. Nov 12, 2018 at 7:22 PM
    #31
    Wunhunglo

    Wunhunglo Member

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    We welded my cat on so no gasket. What is procedure for cleaning throttle body.
     
  12. Nov 20, 2018 at 5:36 PM
    #32
    Wunhunglo

    Wunhunglo Member

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    3 in lift, 33's, and steelies
    Finally got mine fixed. Was the rear 02 sensor. 80 bucks sensor and labor. Wasn't that bad at all.
     
    outlawtacoma likes this.
  13. Nov 20, 2018 at 5:58 PM
    #33
    outlawtacoma

    outlawtacoma Well-Known Member

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    That’s good to hear.
     
    2ndToy likes this.
  14. May 14, 2019 at 6:03 AM
    #34
    Six Volt

    Six Volt New Member

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    Can someone explain this sentence? What is meant by the "activity?" Is it measuring CO2 or some other gas? What is "approaches the waveform?" Does that mean they (front and rear sensors) are reading at or close to the same level? or 80% the same? (That is, less than a 20% difference?)

    Thank you.
     
  15. Aug 20, 2019 at 6:44 AM
    #35
    sonoran

    sonoran My main Taco

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    Flagstaffrica, AZ
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    Tacoma 4X4 3RZ
    BF Goodrich TA KO2 235/85-16 Matching Spare (in rotation) Custom Alcan rear springs OME greaseable shackles King 2.5 rear shocks King 2.5 Front coil overs Total Chaos upper UCAs Total Chaos Steering knuckle gussets Total Chaos Steering rack bushings RAD Rubber splash guards ARB Rear locker ARB HD Compressor Rear diff breather extended Custom full-coverage skid plates Stubbs welding sliders CBI rear frame plates CBI rear bumper Washable air filter (with spare for trips to Baja) Optima Red Top Custom over spring exhaust Spray-in bed liner Saddle Blanket seat cover Alpine sound Anza Headlights
    Great write up! My buddy just bought a '01 Tacoma farm truck with a 3RZ that produced that code. I told him to take it the the highway and let her eat. After driving it like it was stollen for a week the code has gone away. Cheers!
     

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