P0420 code
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Northstar Engines and System Technical Discussion Discussion, P0420 code in Cadillac Engine Technical Discussion; Whats wrong, p0420 code on my car, cat is about 3 months old (cheap magnaflow). I floor my car all ...
  1. #1
    brianroark's Avatar
    brianroark is offline Cadillac Owners Fanatic
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    P0420 code

    Whats wrong, p0420 code on my car, cat is about 3 months old (cheap magnaflow). I floor my car all the time at least a couple of times a week but i haven't engine braked from 2nd gear, will beating the car a lot work for the wot? i know i should but I'm a speed demon and my play car isn't done yet.

    what could be the prob here.
    new to recent, ac plugs, ac wires, intake gasket, air filter, fuel injector cleaning. etc.

    I was driving up north and floored my car a couple of times, it looked like coolant steam was spraying out of the rear pipes (night time), was probably carbon or moisture, or just from being cold out.

    this has happened before a month ago when it was warmer though, that time i thought it was the slick roads.

    i used the engine block tester kit, blue fluid that turns yellow if carbon is present from sucking coolant tank air and it stayed blue after 3 retests.

    i have a small coolant leak that I cant find?? kinda freaky hearing about all this hg stuff. I don't think my head threads have corroded yet though. Do all the n*'s have head gasket issues after time because after all the abusing i have done to this car not intentionally, just a hot headed speed demon. i would think the heads would have opened up a little already.

    so what would cause a p0420?

    I have a tech 2 so i could check the 02 sensors and other variables if that will help.


    Thanks,
    Brian

    ps. hey i have casino cash, whats this stuff guys?

    IT guy that is a idiot.

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  3. #2
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: P0420 code

    P0420 - Catalyst system low efficiency. Check all your vacuum connectors - throttlebody top, PCV at the rear cam cover, EVAP system, (parking brake on your car ???), any vacuum line you can get to. If you can, test the after-cat O2 sensor - that's the only one which will trip P0420. FWIW, it's a $55 PITA, but doable up on a lift........

    If no joy, then it's entirely possible that the cat is on its way out. We seem to have had more than a few of these this year.

    No, your hard driving won't hurt the engine. Some small percentage of northstars blow head gaskets - the rest run forever. Don't get paranoid - cross that bridge if you come to it. "Babying" the car won't extend its life one iota.

  4. #3
    ewill3rd is offline Cadillac Technician
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    Re: P0420 code

    You answered your own question
    cheap magnaflow

  5. #4
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: P0420 code

    ...............

  6. #5
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: P0420 code

    Do all the n*'s have head gasket issues after time
    No...

  7. #6
    chacenbra is offline Cadillac Owners Member
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    Re: P0420 code

    Quote Originally Posted by ewill3rd View Post
    You answered your own question
    +1... These cars rarely like anything but standard AC DELCO parts.

  8. #7
    brianroark's Avatar
    brianroark is offline Cadillac Owners Fanatic
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    Re: P0420 code

    I reset the code and it hasnt came back in a weeks time so far, I'm going to hook up my vaccum guage and see what my readings are. How can I tell if the second O2 sensor is lazy using a tech 2 and not a multimeter?

  9. #8
    ewill3rd is offline Cadillac Technician
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    Re: P0420 code

    A bad O2 sensor will set codes for a bad O2 sensor.
    The diagnostics must run and pass on the O2 sensors before the catalyst efficiency test can even run.
    Sure check to be certain that you don't have any other problems then replace that cheap converter that isn't working with one that will.

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