P0420 (catalyst) code

Discussion in 'General Motoring' started by MAT, Sep 16, 2005.

  1. MAT

    MAT Guest

    My 2002 Civic Si threw a MIL, P0420 (catalytic converter operating under
    efficiency threshhold). I'm now very concerned because of the 80k/8 year
    catalyst warranty of which my car is now at 79.4K miles!. I cleared the
    code and it has not come back in ~100 miles. Now I intend to do the
    diagnostic test in the FSM. It entails start the car, hold at 3000 rpm
    until radiator fan comes on, then drive 30 seconds in 4th gear between 55-62
    mph, and close the throttle for 1-2 seconds and repeat 4 times. I plan on
    doing this procedure late tonight or tomorrow night when I can do this
    somewhat peculiar maneuver. My concern is that it looks like it would be
    easy to get a false negative. Does the step where I hold rpms at 3k trigger
    some diagnostic mode or is it to ensure a properly warmed engine? Could I
    do this on the way home from somewhere at operating temp or does the
    ommision of the 3k step nullify the result? Should I bother sending a
    dealer or Honda a letter stating what happened in case it comes back after
    80k, will it help with a good faith repair? The procedure is supposed to
    either trip the MIL again indicating a bad TWC or if not, to be considered
    an intermittent failure where the code is cleared and life goes on. I am
    hoping for the latter or a replacement before 80k, thanks!
     
    MAT, Sep 16, 2005
    #1
  2. MAT

    Woody Guest

    WHY did you reset it? Your only hope now is it comes back before the 80k. A
    letter will mean nothing to Honda. Chances are the dealer would have reset
    it also but you would then have proof it failed before 80k.
    Since you are playing with an OBDII tester compare the front and back O2
    sensors and see if catalyst is not working. Also see if the non-continuous
    run cycles are complete. It could take a week for some to complete depending
    on your driving habits. They all got reset when you reset the code. The
    catalyst efficiency test has to be complete before the code will be set....
     
    Woody, Sep 16, 2005
    #2
  3. MAT

    Woody Guest

    WHY did you reset it? Your only hope now is it comes back before the 80k. A
    letter will mean nothing to Honda. Chances are the dealer would have reset
    it also but you would then have proof it failed before 80k.
    Since you are playing with an OBDII tester compare the front and back O2
    sensors and see if catalyst is not working. Also see if the non-continuous
    run cycles are complete. It could take a week for some to complete depending
    on your driving habits. They all got reset when you reset the code. The
    catalyst efficiency test has to be complete before the code will be set....
     
    Woody, Sep 16, 2005
    #3
  4. MAT

    MAT Guest


    Shucks! In hindsight, I wish I didn't clear the code! Damn you RAMH for
    making us competent and self proficient Honda owners! :) Unfortunately I
    have no scanner, just a paper clip. I guess I'll have to try the test
    procedure and see if I can trip the code again. Could a bad tank of gas
    cause this? I took a trip up to NJ from VA and got gas from a shady looking
    Getty, I thought maybe the gas guy just didn't twist the cas cap enough
    clicks but the code was not the evap canister one. :(
     
    MAT, Sep 16, 2005
    #4
  5. MAT

    MAT Guest


    Shucks! In hindsight, I wish I didn't clear the code! Damn you RAMH for
    making us competent and self proficient Honda owners! :) Unfortunately I
    have no scanner, just a paper clip. I guess I'll have to try the test
    procedure and see if I can trip the code again. Could a bad tank of gas
    cause this? I took a trip up to NJ from VA and got gas from a shady looking
    Getty, I thought maybe the gas guy just didn't twist the cas cap enough
    clicks but the code was not the evap canister one. :(
     
    MAT, Sep 16, 2005
    #5
  6. MAT

    MAT Guest

    The code came back and I have a service appointment for Wednesday, will have
    about 79,800 miles by then. What does the P0420 usually lead to? Cat,
    secondary 02 sensor replacement? Both? Thanks.
     
    MAT, Sep 19, 2005
    #6
  7. MAT

    MAT Guest

    The code came back and I have a service appointment for Wednesday, will have
    about 79,800 miles by then. What does the P0420 usually lead to? Cat,
    secondary 02 sensor replacement? Both? Thanks.
     
    MAT, Sep 19, 2005
    #7
  8. I had my Catalyst go bad in my 98 civic after a tank of bad gas. Filled up
    at this place my buddy swore by cuz they gave a cash discount. Also noticed
    that the fuel smelled like nail polish remover while filling up. Shoulda
    been my first clue. The whole way home from Regina to Winnipeg the car was
    bucking and sputtering, about a week later the catalyst went bad.
    Fortunately Honda covered it. Not before they reset the ECU twice though. I
    think I got an O2 sensor out of the deal too. They reuse them unless they
    can't free them from the old manifold.

    t
     
    T L via CarKB.com, Sep 19, 2005
    #8
  9. PS they did try to blame this on the famous loose gas cap, even though the
    code was clearly for the catalyst. whata bunch of gearboxes.

     
    T L via CarKB.com, Sep 19, 2005
    #9
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