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420 "low efficiency code" engine light

This is a discussion on 420 "low efficiency code" engine light within the General Help forums, part of the LSx Technical Help Section category; My 1999 Firehawk keeps giving the 420 "low efficiency code" engine light; I can't pass NC emmisions inspection. The pontiac ...

  1. #1
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    Exclamation 420 "low efficiency code" engine light

    My 1999 Firehawk keeps giving the 420 "low efficiency code" engine light; I can't pass NC emmisions inspection. The pontiac dealership checked out everything to no avail. I bought the car used with headers, and custom universal cats, worked fine for a year, now have replaced 2 bad downstream O2 sensors, and just had new universal cats installed, yet still it throws up the code after driving about 20 miles or so....have cleared the code twice but it keeps coming back. Any ideas? I hate to have to shell out more $$$ for stock manifolds after dropping over $500 on new cats.

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    Life in the Fast lane sunsetorangess's Avatar
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    Why did you replace the downstream sensors?
    The code started poping up when you instailed the universal cats right? If so then i would say your problem lies within the cats.
    J
    2001 SS, Its not the car its the Driver that matters....

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    O U 8 1 2 Spaz's Avatar
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    do you have a sniffer test there??? if not jsut pay some one to hallow out your cats... that is what i did... now i said to hell with them and completely got rid of them...

  4. #4
    Member crazy dave ls1's Avatar
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    the p0420 code is set by monitoring what the pre and post o2 are doing.usually the pre and post o2 are switching at the same rate or mirror image of each other to set this code witch means the cat sux.I work at a reputable shop and have had problems with universal cats before.A friend of mine uses 02 emulators without cats but where he got them no longer carries them

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    Would it pass an emissions test?

    Quote Originally Posted by crazy dave ls1 View Post
    the p0420 code is set by monitoring what the pre and post o2 are doing.usually the pre and post o2 are switching at the same rate or mirror image of each other to set this code witch means the cat sux.I work at a reputable shop and have had problems with universal cats before.A friend of mine uses 02 emulators without cats but where he got them no longer carries them

    Good advice, So I found a place that sells the O2 simulators...do you know if it would pass an emmisions test with the simulators....assuming the new cats are doing their job? (I just wonder if the computer can tell the difference in the simulators or working O2 sensors)

  6. #6
    Member crazy dave ls1's Avatar
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    as long as the state inspector isnt very thorough. its my understanding the sims attach to the rear o2s so unless he raises the car he wouldnt see them.if you have access to a code reader or scanner it would be easier to know, so all you can do is install them disconnect the batt to reset the computer and put about 50 miles on it.if theres no light you should be good.if it works please let me know so that i can remove my cats

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    Senior Member Bottesini's Avatar
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    Another solution is to get a tune which will delete the emission codes from your PCM. You will never have to worry about any O2 sims going out or anything else really. Only thing you have to worry about then is if they do a visual, or if you live in someplace like CA where they are very strict about the emissions. For the price of sims I would bet that is close to a mail order tune by Frost, but at least with a tune you also get a few more goodies added in along with extra performance.

  8. #8
    Member crazy dave ls1's Avatar
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    is there a reputable tuner in our area?can they also get rid of AIR codes?can i get any benifit from them on a stocker daily driver?I'm sorry to ask so many questions but I'm old school this is my first ls1 and you dont know unless you ask.thanks for your patience
    Last edited by crazy dave ls1; 08-13-2008 at 03:27 PM.

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    Life in the Fast lane sunsetorangess's Avatar
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    I passed with 02 sims. You can leave the stock sensors in place, just disconnect the harness and plug in the sims and tuck them away so they wont be seen.
    J

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    Senior Member Bottesini's Avatar
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    Quote Originally Posted by crazy dave ls1 View Post
    is there a reputable tuner in our area?can they also get rid of AIR codes?can i get any benifit from them on a stocker daily driver?I'm sorry to ask so many questions but I'm old school this is my first ls1 and you dont know unless you ask.thanks for your patience
    When I pay a shop to work on my car I use RPM in Lewisville. I have found they are one of the best priced shops in town, and I get along with the guys there. They can also get you dynotuned, when they first tuned my car which had long tube headers, and true dual exhaust as basically my only mods the car picked up 21 RWHP throughout the curve. No to mention all the other stuff that I no longer had to deal with (all the emission stuff, skip shift, etc). It is expensive up front, but the nice thing is whenever you need another tune you do not pay near as much for retunes. Whiter it is worth it or not all depends on you and your plans. If you plan on doing alot of stuff soon, you might want to hold off. If you will be adding stuff slowly, you might want to get a tune earlier in the game.

    I came from a fairly old school understanding myself, but I have found the LS engines to be something that has been worth jumping in with both feet. Keep an eye on the Texas train we have get to gathers fairly often in the DFW area, you are more then welcome to join in.

  11. #11
    Member crazy dave ls1's Avatar
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    would love to attend just let me know when and where.

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    any good tuning shops around Charlotte NC?

    Anyone know of any repuatble tuning shops with ls1 edit near Charlotte/Conord NC?

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