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po420 code

This is a discussion on po420 code within the General Help forums, part of the LSx Technical Help Section category; will driving the car with this code on 4 1 week hurt anything? (cat low efficiency) Is there a code ...

  1. #1
    Junior Member
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    01 M6 SS Turbo

    po420 code

    will driving the car with this code on 4 1 week hurt anything? (cat low efficiency) Is there a code for a plugged cat? A cat that still flows but doesn't clean is okay, but a plugged one is a no no for limping along until gm gets the new one.

  2. #2
    The Bandit Wesman's Avatar
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    1998 Trans Am WS6

    The fact that the catalytic efficiency is "below threshhold" won't hurt the car or your engine at all. Its merely bad for emissions.

    However, if the cat is plugged up, then that is definitely bad for your engine. There is no code for that, the O2 sensors merely detect whether the cat is cleaning the exhaust properly, not whether it is flowing well.

    If you feel any decrease in power, the cats are probably getting plugged up. Good time to install some LT headers

  3. #3
    Member 79Firebird_99TA's Avatar
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    Quote Originally Posted by matt89 View Post
    will driving the car with this code on 4 1 week hurt anything? (cat low efficiency) Is there a code for a plugged cat? A cat that still flows but doesn't clean is okay, but a plugged one is a no no for limping along until gm gets the new one.
    Been there - done that.....with a `01 Maxima. You need a catalytic converter. You have an o2 sensor upstream and downstream to that CC. The downstream o2 is measures the efficiency of the CC.

  4. #4
    Senior Member SeVeReDiStOrTiOn's Avatar
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    The light is annoying but the car will be ok...the cats will probably have to be replaced to pass emissions though. I had a p0420 and just tuned the code out...still passed hippie cali emissions.

    Did you ever get that letter from GM? They extended the cat warranty to 100k if I remember right...

  5. #5
    Member 79Firebird_99TA's Avatar
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    Quote Originally Posted by SeVeReDiStOrTiOn View Post
    Did you ever get that letter from GM? They extended the cat warranty to 100k if I remember right...
    No....I never did. The girl that had the car divorced me....LOL.
    Now it's her problem.

  6. #6
    TunedByFrost supporter rel3rd's Avatar
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    Quote Originally Posted by SeVeReDiStOrTiOn View Post
    The light is annoying but the car will be ok...the cats will probably have to be replaced to pass emissions though. I had a p0420 and just tuned the code out...still passed hippie cali emissions.

    Did you ever get that letter from GM? They extended the cat warranty to 100k if I remember right...
    FWIW,
    My letter from GM says 130,000 miles...

  7. #7
    Senior Member SeVeReDiStOrTiOn's Avatar
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    Quote Originally Posted by rel3rd View Post
    FWIW,
    My letter from GM says 130,000 miles...
    Sweeeeet...even better

  8. #8
    Junior Member 7901 ws6's Avatar
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    Its a CAT. I had that code when My car was at 25K, the Repair under Warranty was replace the CAT.

  9. #9
    Junior Member madmatt's Avatar
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    Yep, dealership replaced mine under warranty.

  10. #10
    2001 Pewter WS6 ws6drew's Avatar
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    Pewter
    2001 WS6 Trans Am

    I've got the same error code and the same letter from GM (also meaning I sill have the Service Engine Soon light on). When they replace the cat's will I need to replace the sensors too? If so, how difficult is it to do that? Not a huge fan of giving the dealership a shitload of money for something I can do myself... just need a little guidance
    WS6DREW

  11. #11
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    Know people who have had their cat replaced under the warranty - didn't have to spring for new sensors. 99% of the time P0420 or P0430 is the cat, and the sensor is doing what's it's supposed to - monitor the cat.

  12. #12
    2001 Pewter WS6 ws6drew's Avatar
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    Good call, thanks man!

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