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Please Help with code P0420

This is a discussion on Please Help with code P0420 within the General Help forums, part of the LSx Technical Help Section category; Hello Everyone, My 01 Z28 has 48,000 miles on it.I took it to the local parts store when the SES ...

  1. #1
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    2001 Z28

    Please Help with code P0420

    Hello Everyone,
    My 01 Z28 has 48,000 miles on it.I took it to the local parts store when the SES light came on.He scanned the computer and code Po420 popped up.
    Catalyst efficiency Bank 1 below threshold.Not knowing exactly what that was myself ,he told me it was the o2 sensor behind the cat.So I bought it from him for $64 dollars (Bosch)installed it as soon as I got home.Went back to them and they cleared the code .2 days later it is back on.He cleared it again and the next afternoon it is back on.It does seem to idle a little rough but smoothes right out and runs fine under throttle.I still don't Know what the code means for sure.Is it an o2 or the actual cat and how much is a new cat and the best place to get one.
    Thank you for any help I can get.
    Brent McMillan

  2. #2
    Senior Member SeVeReDiStOrTiOn's Avatar
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    05 Wrangler
    00 Z28 sold :-(

    I had the same code and replaced the cat....it's been 7 months and hasn't been back. I got the random-tech Y-pipe and both cats at the sites sponser thunder racing...here's a link
    http://thunderracing.com/catalog/?ac...&vid=3&pcid=99

    The build quality and fit is great...and the Y is a 2.5in and the cats are high-flow so it flows better then stock. Before I bought the RT cats I priced the cats individually....dealer wanted around $400 a pop...same with a local exhaust shop for the Car Sound(magnaflow) cats.

    BTW the cats are covered under a federal emissions act for 8yrs/80,000mi....unless you have a california car and it's only good for 7yrs/70,000mi, I found that one out the hard way So if your car fits in there....wait until it throws the code again, keep the code in there and bring it to the dealer.

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    Thanks alot!
    We bought the car used from a dealer and bought the 4 year extended warranty and our deductible is $100.Thanks for the help.

  4. #4
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    You shouldn't have to pay any ded; know people who had their's replaced and didn't have to pay anything.

  5. #5
    LS1 Noob
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    Red
    2000 WS6

    Kind of late now, but what you should have done was swap the passenger and driver side O2 sensors to see if the code moved to the passenger side. If the code doesn't move... then you have a bad cat on the driver side. If the code moves to the passenger side, then you have a bad O2 sensor.

    This doesn't take a great amount of time, but gives you a better idea what your problem really is.

    Do a search on the various forums and you'll find that the exhaust system is warrantied for something like 7 years or 85K miles. So long as your car falls in there, they should replace the cat for free.

    Marc

  6. #6
    Senior Member mrr23's Avatar
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    dark bowling green
    2000 corvette

    Quote Originally Posted by Mac500r
    Thanks alot!
    We bought the car used from a dealer and bought the 4 year extended warranty and our deductible is $100.Thanks for the help.
    the cats are covered for 8 years 80k miles for free. i've had mine replaced at the dealer for free. don't let them con you into using your extended warranty.

  7. #7
    Old Enough to Know Better Crimson Sin's Avatar
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    Red Fire
    2007 Mustang GT/CS

    I had a similar code P0430 ( other side I b'lieve) ".. bank 2 catalyst emissions below acceptable threshold.." or somesuch, Dealer installed new cat on passenger side w/ no issue's at all, even thanked me for driving a GM ..
    Service desk said Federal Law mandates 8/80 k on all cats et cetera.

  8. #8
    Rice Hungry GottaHaveLS1's Avatar
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    Black
    1999 Trans Am M6

    When you get the 420 code, it means you need to bake out ur car.
    1999 Trans Am M6
    SLP Short Throw, Lid and CAI, BMR STB and SFC, UMI PHB, Pacesetter LT's and ORY, Magnaflow Catback, DMH 3" E-Cutout, LS7 Clutch, Motive 4.10, 160 T-Stat, MSD, !AIR, !EGR, 17x9.5 Chrome C6's wrapped in Hankook 275/40/17

    Tuned at Mongillo Motors in New Haven, CT

  9. #9
    Senior Member Hurley711's Avatar
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    414 RWHP 395 RWTQ
    00 Black Ram Air Trans Am

    8/80k is correct. My dealer replaced both cats and both O2 for FREE

  10. #10
    Senior Member Danger731's Avatar
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    Quote Originally Posted by GottaHaveLS1
    When you get the 420 code, it means you need to bake out ur car.
    Nice

  11. #11
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    Thanks for all the help and opinions,except I don't understand the "Bake out ur car"
    I called the local dealer and set up an appointment to get i fixed.The dealer said the same thing.8/80 warranty.
    Thanks,
    Brent

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