Thread: p0420 code, which o2 sensor do i replace?

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  1. #1 p0420 code, which o2 sensor do i replace? 
    SE Level Member Golman76's Avatar
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    i have a p0240 code and i have concluded that i need to replace an o2 sensor. It says bank 1, but does not state sensor 1 or sensor 2. if it is the one on the cat, will the spark plug non fouler go-around fix my problem?

    say the o2 sensor is blown or clogged, will the non fouler fix still fix it? or do i still need to replace the sensor?
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  2. #2 Re: p0420 code, which o2 sensor do i replace? 
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    code P0420 means that the PCM does not see the proper change in exhaust gas after the primary CAT, this could be a clogged CAT or your secondary O2 (the one after the primary CAT) is bad.
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  3. #3 Re: p0420 code, which o2 sensor do i replace? 
    Your ClubGP Liason copgtp's Avatar
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    spark plug non fouler go-around fix my problem
    I might live under a rock, but can you explain this for me?
    For all your 3800 needs:
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  4. #4 Re: p0420 code, which o2 sensor do i replace? 
    SE Level Member GTPcoupe's Avatar
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    Does it say "PO420 catalyst system efficiency below thresh hold (bank 1)"? If so, I would say the rear 02 sensor.
    '99 GTP coupe - Growing mod list/summer car
    '98 GTP Sedan - Winter ride, 315,000+kms and going strong!
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  5. #5 Re: p0420 code, which o2 sensor do i replace? 
    SE Level Member GTPcoupe's Avatar
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    Quote Originally Posted by copgtp View Post
    I might live under a rock, but can you explain this for me?

    This is useful if you have a hi flow cat that sets off the engine light and dont have a custom tune that deletes the code. It's just a peice you screw on to the end of the 02 sensor and then screw it in the pipe. It pulls the sensor back out farther so it detects less and tricks the sensor.
    '99 GTP coupe - Growing mod list/summer car
    '98 GTP Sedan - Winter ride, 315,000+kms and going strong!
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  6. #6 Re: p0420 code, which o2 sensor do i replace? 
    SE Level Member Golman76's Avatar
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    yes gtpcoupe that is what it says. So if i use the non foulers will that make it good as new?
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  7. #7 Re: p0420 code, which o2 sensor do i replace? 
    SE Level Member GTPcoupe's Avatar
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    Quote Originally Posted by Golman76 View Post
    yes gtpcoupe that is what it says. So if i use the non foulers will that make it good as new?
    It would probably stop the code from coming up, but you should see if it's the sensor or if you do have a clogged cat.
    '99 GTP coupe - Growing mod list/summer car
    '98 GTP Sedan - Winter ride, 315,000+kms and going strong!
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  8. #8 Re: p0420 code, which o2 sensor do i replace? 
    SE Level Member Golman76's Avatar
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    how do i see if it is the sensor?
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  9. #9 Re: p0420 code, which o2 sensor do i replace? 
    GTX Level Member OH4CompG's Avatar
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    Your rear o2 sensor almost never goes bad. Replace your cat
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  10. #10 Re: p0420 code, which o2 sensor do i replace? 
    GTX Level Member 97gtsc's Avatar
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    Just delete both problem solved
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