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Help with code.....

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by Oscarvan, Jan 26, 2010.

  1. Oscarvan

    Oscarvan New Member

    On the Suburban I have an intermittent "service engine light" which I understand to mean that there is an intermittent condition, that after it goes away will result in a number of "clean" starts (I think it's 5?) and then goes out. A few days later it will come back and so on and so forth....

    The code is a P0420 which the generic code reader defines as:

    "Catalyst System Below Efficiency Bank 1"

    Now what?
  2. LowcountrySuburban

    LowcountrySuburban New Member

    Could be a bad catalytic converter.
  3. Oscarvan

    Oscarvan New Member

    Could be.....but I'm looking for a more systematic approach.
  4. Oscarvan

    Oscarvan New Member

    OK, ended up with a subscription to Alldata....

    Have to check the obvious but then it sounds indeed like the converter is toast.
  5. LowcountrySuburban

    LowcountrySuburban New Member

  6. Oscarvan

    Oscarvan New Member

    Not yet.... The truck runs just fine, I have until next inspection (December lol).

    I think I will replace the O-2 sensors first..... (four of them). They get lazy anyways, and have 127 K on them.
    Then I suspect the Cat will have to be replaced. All in all about $600......:frown:

    I have no plans on selling this truck anytime soon.....I've had it since new, it's a part of the family.
  7. MrShorty

    MrShorty Moderator Staff Member 1000 Posts

    One of the first things I did in the same situation (actually had a P0430, but the same idea) was to swap the two post cat sensors. If the code follows the sensor (meaning, if you start to get a P0430 instead of a P0420), then you have a good indication that the sensor/wiring is going bad. If the code remains the same, then it's probably not a problem with the sensors.
  8. Oscarvan

    Oscarvan New Member

    I like it! Thanks.

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