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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 29, 2018 at 12:09 PM
    #21
    JT1521

    JT1521 [OP] Well-Known Member

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    Got a good video on how to clean the MAF sensor and throttle body showing what to disconnect and properly clean on a 2003 Tacoma?
     
  2. Sep 29, 2018 at 1:50 PM
    #22
    MalinoisDad

    MalinoisDad Well-Known Member

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    I had a bad air/fuel ratio sensor (I think) (middle of exhaust somewhere) that would actually work fine when I held the wires in a certain position. Therefor, the CEL was intermittent. I ultimately found this out by using my multimeter set to ohms (resistance), inserting the probes into the ends of the sensor wire after you disconnect the electrical connector. In certain positions the sensor had resistance/continuity, and in others it was an open circuit/short. Replacing the sensor cleared the code and it hasn't come back in over a year.

    Part of what helps me learn a wee bit faster on stuff like this is my 12+ years of working on hot tubs as a technician, as random as that sounds. Electrical troubleshooting and repair, plumbing, even carpentry, etc. Base mechanical aptitude in general is helpful when trying to learn new things :)

    But I know enough to know I don't know much.
     
  3. Sep 29, 2018 at 2:22 PM
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    onakat

    onakat Well-Known Member

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  4. Oct 3, 2018 at 9:54 AM
    #24
    JT1521

    JT1521 [OP] Well-Known Member

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    He never does mention disconnecting the negative battery terminal before doing this. Should I?
     
    Last edited: Oct 3, 2018
  5. Oct 3, 2018 at 10:35 AM
    #25
    JT1521

    JT1521 [OP] Well-Known Member

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    IMG_2665.jpg Also here is a picture of where my Throttle body and where my MAF sensor is. It's pretty simple to take off the MAF to clean it but what is the easiest way to remove that intake hose off to get to the throttle and spray it. I would rather not take off more than I have to just to clean it. Thanks.
     
  6. Oct 4, 2018 at 8:43 AM
    #26
    onakat

    onakat Well-Known Member

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    you can disconnect the battery, if you want to, but it's not necessary

    Well, it's not that hard to remove the intake hose. You just unclip the airfilter cover then undo the collar/clamp thingy that is holding it to the throttle body. It will slide right off.

    The with the air filter cover out, it will give you access to the MAF sensor (good view of it when you turn it around)
     
  7. Oct 4, 2018 at 12:35 PM
    #27
    JT1521

    JT1521 [OP] Well-Known Member

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    Well I just cleaned the MAF sensor and Throttle body. I disconnected the battery before doing so. Started up the truck after I was done. White smoke came out for a couple minutes until it dissipated. I read where that is normal. The CEL turned off from the battery being unplugged. Now I just sit and pray it doesn't come back on. I have my doubts this is what caused the CEL. Lol.
     
  8. Oct 4, 2018 at 12:41 PM
    #28
    eon_blue

    eon_blue Straight Outta 4WP

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    Not to sound like a pessimist but I'm betting that it will. P0420 is an emissions related code so I don't see how cleaning the TB and MAF would help...maybe if it were a PO171 code or similar.

    When I got the dreaded P0420 code, I tried all sorts of things and reset it by disconnecting the battery and it would always come back...sometimes right away, sometimes after a few hundred miles. Once the ECU completes the emissions cycle it will see something is wrong and trip the code again.

    Ended up that my front cat was bad, I replaced both with CA approved Magnaflows (OEM cats are crazy expensive). Code went away and has been gone for a year now.
     
    OneWheelPeel likes this.
  9. Oct 4, 2018 at 3:52 PM
    #29
    onakat

    onakat Well-Known Member

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    The thing with P0420 is that it can be caused by such a wide range of things, it's hard to pinpoint what can cause it. So you have to go trial and error, ruling out simpler things first. Yes, it does tells you that the cat is below efficiency, but that does not necessarily means the catalytic converter is bad. Lots of things can foul the sensor readings, making them read data as if the cat was bad.

    Also cats don't go bad on their own. You have to have had rich or lean issues for a while, destroying the cats from the inside.

    Anyways, if it does come back, next step would be to check for exhaust leak. Easy to test with an homemade smoke machine:
    https://www.youtube.com/watch?v=BP2ffBSD2A0
    He did use it for a vacuum leak, but the principle is the same. Just connect it to your exhaust pipe instead
     

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