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OBDII error code p0420

This is a discussion on OBDII error code p0420 within the Computer & Tuning forums, part of the LSx Technical Help Section category; Service engine soon light is on and i just go it scanned at autozone. The error was "p0420 the catalyst ...

  1. #1

    Question OBDII error code p0420

    Service engine soon light is on and i just go it scanned at autozone. The error was "p0420 the catalyst system efficiency for bank 1 is below threshold for the current operating conditions etc..." (looked online and such for information) any one know what the fix for this is. I think it could be a broken 02 sensor (in which case i would get a volt meter to test and double check this and replace if it is damaged). beyond that, what other problems could it be? Damaged or clogged cat? how would i tell exactly? is the best thing to do is check the o2 sensor first, then work my way from there?

  2. #2
    i would check ur 02 sensor for bank 1...sometimes that code will throw because of a bad ground...a common gm fix is to attach a grounding strap from a bolt on a flange somewhere close to the sensor and then somewhere on the body... good luck and keep us posted

  3. #3
    Senior Member
    Join Date
    Jul 2005
    Jacksonville, FL

    There's even more threads - search for "P0420"

  4. #4
    yeah i searched "4020" with nothing.. i forgot to put the "p".. found the info i needed thx

  5. #5
    I have a 420 and a 430 code they tell me the cats are bad

  6. #6
    Senior Member SeVeReDiStOrTiOn's Avatar
    Join Date
    Aug 2005
    Roseville, CA

    05 Wrangler
    00 Z28 sold :-(

    The cats can also be the effect...and not the cause. The cat could be bad...but what made it go bad? Running rich can do it...blown head gasket, i'd find out the main problem before replacing the cat. But it could also just be the cat, every situation is different.

  7. #7
    Senior Member Hurley711's Avatar
    Join Date
    Jul 2005

    414 RWHP 395 RWTQ
    00 Black Ram Air Trans Am

    Had same code, both cats were bad, both were replaced for FREE under gov't mandated 8yrs/80k mile waranty

  8. #8
    what kind of symptoms come about with a blown head gasket or running rich?

  9. #9
    I like the way yew tawlk. Ric's Avatar
    Join Date
    Aug 2005
    Blairsville, GA

    2000 T/A WS6

    Blown head gasket? Check your oil and coolant. If you have oil in the coolant, or coolant in the oil, then you also have a blown head gasket.

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