P0420 after cat replaced

Discussion in 'General Motoring' started by goldenset, Feb 13, 2005.

  1. goldenset

    goldenset Guest


    Need to find out what my next step is. Got a Honda Prelude, 1999, with
    180K highway miles. I just replaced the cat since the engine light came on
    a few months ago, plus my emissions/smog test was due soon. Even the dealer
    told me the light is a likely indicator for a new cat, AND it's OK to drive
    it until I'm due for my registration renewal.

    So I replaced it two weeks ago. I was also informed that my cat had a
    built in O2 sensor, hence it was expensive. So I drive it around a little
    bit but the light didn't go off. So I decided to fork the money over to at
    least get the emissions test and find out what else is failing. All passed,
    except the MIL because the light is still on.

    Tech also said do not disconnect the batter because that resets the
    computer, and it'll push me about 1 week of driving since the computer has
    to be in it's pattern (whatever that means). highway driving is not enough
    because it's reading "high" speed? Dunno why that matters.

    The emissions test center said I have another sensor at the top that most
    likely wasn't replaced. Is this true? More than 1 cat sensor?

    My registration renewal is due next week. The MIL light turned off. But it
    has been on-off in the past few months also. I'm wondering if it's off due
    to increased stop-n-go driving in the city recently, and the computer is
    in its "normal" pattern. I'd like to avoid having to go for another test
    to see if it'll pass.

    What do you folks recommend?

    Thanks in advance.
    goldenset, Feb 13, 2005
    1. Advertisements

  2. goldenset

    jim beam Guest

    yes, you definitely have two sensors - one just before, one just after
    the cat. code P0420 is "Catalyst System Low Efficiency". if you have
    the same code both before & after replacing the cat, you can be pretty
    sure it's the sensor.
    jim beam, Feb 13, 2005
    1. Advertisements

  3. "goldenset" wrote
    Any excuse to replace a cat is ok with me, as long as you don't get another
    Howard Lester, Feb 14, 2005
  4. goldenset

    chip Guest

    notice he never said the light was reset at time of cat replacement.
    and the o2 sensor is not built in, it screws in just like the rest.
    they should have cleared the codes and done the idle learn
    chip, Feb 14, 2005
  5. "chip" wrote
    I know exactly what he said. He and you are talking about cats. I'm
    suggesting perhaps he get a dog instead. Dogs learn "idle" very quickly.
    Howard Lester, Feb 14, 2005
  6. goldenset

    goldenset Guest

    the cat replacement wasn't done by a dealer. rather a small mom/pop shop.
    now i wonder if the quality was even there since the time it took was too

    i did want to go to the dealer to ask a buddy to reset it for me. but
    that's when a local smog shop said don't (explained in my earlier post).

    all in all, the light finally went off. I've been driving in the city a
    bit in the past two weeks. light went off, and never came back on. so i
    decided to get another smog test today given the mil was the point of
    failure last time.

    and.... it passed. maybe it does take some time for the system to
    recalibrate itself w/o resetting the codes?
    goldenset, Feb 15, 2005
  7. goldenset

    Lex Guest

    what did you replace it with and where? a Honda cat? the oxygen sensor isn't
    "built in", its screwed in just like any other o2 sensor.
    Lex, Feb 23, 2005
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.