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Thread: P0420 Catalyst Efficiency Below Threshold

  1. 04-08-2021 #1
    pjs
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    P0420 Catalyst Efficiency Below Threshold

    Hello,
    I have a 2009 Base Vette LS3 with A&A kit w/Meth and just got the P0420 code recently.
    Car has 28K miles so I figure I'd just replace the CATs but won't have the funds for a couple months.
    So...Was thinking of just disabling the P0420/P0430 codes for now.

    I searched a bit but mostly deals with disabling the O2s and CAT tests all together, which I'd like to avoid.
    Any side affects of just disabling these 2 codes for now, e.g. will emissions tests go complete, etc?

    Also noticed one possible related tune setting change that I'm not sure if it was changed to help avoid this or maybe caused this prematurely?

    It's in: Engine Diag/Exhaust/Downstream/Lean Thresh. The stock value was 350mv. The A&A base tune that I started out with has it at 300mv.
    Anyone know if this better or worse or not related to P0420?

    Searching CF also indicated there was a TSB at some point on these CATs due to tune/setting being too sensitive.
    Anyone know if/where this setting is?


    Thanks,
    Pjs
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  2. 04-08-2021 #2
    pjs
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    I'm reading that non-foulers solves this problem so....Going to replace the CATs then install non-foulers if the code comes back with new CATs.


    Pj
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  3. 04-08-2021 #3
    5FDP
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    I'd just disable the codes and carry on. You'll know if the cats become an issue if there is a power loss or they start glowing red because they are plugging up. Or the smell of the exhaust changes because they aren't working at all.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.
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  4. 04-08-2021 #4
    gottogo
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    I wouldn't buy new cats AND install non-foulers. There may be nothing wrong with your cats as you already mentioned.
    Get the non-foulers and keep looking into the sensitivity issue.
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  5. 04-09-2021 #5
    pjs
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    Thanks guys. Seems I can just install the foulers or disable the codes for now. Appreciate the feed back.


    Pj
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  6. 04-10-2021 #6
    village_idiot
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    If you are simply not wanting to see the CEL for now, you could also just set the codes to "No MIL Light" and it will keep the MIL in the background with no light for that code. Then, if you run a diag scan, it'll be there. Just a thought if this is temporary to not have to look at a light
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