P0420 Trouble Code ??

Discussion in 'General Motoring' started by Nick Lamendola, Sep 27, 2006.

  1. Hello,

    I have a P0420 trouble code, that says "Catalyst Efficiency Below
    Threshold". Can any one give me an idea on how to raise the efficiency of
    the catalyst? My car is a '99 2.5L Legacy Outback wagon w/ 113K miles. Is
    this trying to tell me I need to replace the catalytic converter on the
    exhaust system? Sounds like it going to hurt my wallet. I've searched past
    posting and didn't find anything. Anny and all help is appreciated.

    Nick Lamendola, Sep 27, 2006
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  2. Nick Lamendola

    mulder Guest

    Yeah sorry you can't raise the catalyst efficiency, that code is
    telling you the catalyst is shot. At 113K that is not surprising.
    Unfortunately you are well past the federal emissions warranty period
    of 8/80 or you could have gotten a new one for free.
    Depending on what state you reside in and whether you need to pass
    inspection, you may be able to forgo this repair at least for the time
    being (as long as you don't mind staring at the light) or you may have
    to do it to pass emissions.
    mulder, Sep 27, 2006
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  3. Thanks mulder, I really didn't have much hope in raising the efficiency. I'm
    just happy that my car passed NYS inspection last month. No new inspection
    sticker in NY with a check engine light on. :( I don't mind having the
    catalytic convertor replaced as long as that makes the code go away. I read
    where it could be caused by an exhaust leak. Any idea if muffler shops can
    test a catalytic convertor? I hope it is not an issue with the O2 sensors,
    as that sounds like it can get you chasing your tail. Thanks again,
    Nick Lamendola, Sep 27, 2006
  4. Nick Lamendola

    JD Guest

    That's true. If the leak is before the catalytic converter. Its a much
    cheaper fix though, so I'd have that checked before going to replace the
    catalytic converter. If the O2 sensor goes, it throws its own code.
    JD, Sep 27, 2006
  5. Nick Lamendola

    AS Guest

    Just out of curiosity, what kind of driving style do you have?

    I would imagine smooth driving.
    AS, Sep 27, 2006
  6. First, you MAY have a bad converter - however, there is a very great
    chance what you have is a 'lazy' or bad lambda (O2) sensor. Has an O2
    sensor ever been changed on your car?
    Also, if you clear the code, do you get an immediate return of the CEL?
    The only way the ECU can detect a bad converter, is comparing signals
    from an upstream and downstream O2 sensor. If one of these sensors is
    bad (or associated wiring) you will get that code. The diffence in cost
    between a new converter and a new sensor is close to an order of
    magnitude. So, even if you can't actually get someone you trust to test
    the sensors (easy with a scope or even some meters) it is likely still
    worth the gamble to change the sensors. If you know neither of them have
    eever been replaced, definitely change the front one first and
    drive/monitor the situation. If the front has been replaced in the last
    50K miles or less - it may mean the after cat sensor needs replacing.

    don't panic!

    Carl 1 Lucky Texan, Sep 27, 2006
  7. Thanks Carl,
    I'll take your advise. Neither O2 sensor has been replaced. I cleared the
    code and it hasn't returned in my normal 70ml. round trip commute to work
    today. So maybe it was just a fluke, it happend right after I gassed up my
    car. If it does come back I'll start with replacing the O2 sensors.
    Nick Lamendola, Sep 28, 2006
  8. Nothing too hard, I rarely push it, mostly express way speeds, commuting to
    work and back. Why do you ask?
    Nick Lamendola, Sep 28, 2006
  9. Nick Lamendola

    AS Guest

    I asked because when engines are not driven under demanding conditions,
    carbon tends to build up on pistons and valves. Sometimes, deposits can
    also be formed on oxygen sensors and catalytic converters, when cars are
    driven for short distances, not allowing all these components to get
    real hot.

    One problem i remember due to this was the 4 cylinder camry engine, 95
    model and similars, which used to develope a sticky valve syndrome,
    killing one of the cylinders...

    In your case, express way speeds would exclude this as a possible cause
    for your problem and I second carl's suggestion.

    Good luck
    AS, Sep 28, 2006
  10. Nick Lamendola

    Mickey Guest

    Due to mileage I'm betting on bad converter. There is also
    a code for bad O2 sensors so if you are not seeing that in
    addition to the P0420 code my money is on the converter.

    Mickey, Sep 28, 2006
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