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Thread: Code 420

  1. #1
    Join Date
    Oct 2018
    Location
    Franklin,TN
    Posts
    19
    My Cars
    1997 Z3 roadster

    Code 420

    My 97 Z3 has a 420 code and not really sure what to do. I just got the car about 6 months ago. It has been sitting for awhile due to the owners health issues. I have changed both O2 sensors, replaced the injector “spider” vacuum hoses, plugs, wires, injector cleaner, not sure what to do next. The car has about 90 k miles and has been driven very little in the last 14 years. Any ideas?

  2. #2
    Join Date
    May 2015
    Location
    Springfield Il
    Posts
    74
    My Cars
    '97 Z3
    A P0420 translates to catalytic converter efficiency below threshold. To simplify that means that the cat is not filtering as it should. Most likely means it needs replaced.

  3. #3
    Join Date
    Jul 2013
    Location
    Milwaukee, WI
    Posts
    83
    My Cars
    1998 BMW Z3 2.8
    Not to diagnose by anecdote, but I had this code on an M52 engine and it turned out to be a lean condition due to a vacuum leak; in my case a hole in the lower CCV line.

    US-129

  4. #4
    Join Date
    Mar 2003
    Location
    Willis, TX USA
    Posts
    2,252
    My Cars
    98 MZ3, 01 325iT
    Yeah, don’t jump to conclusions. It could be expensive and you find it’s not fixed. Is that a BMW code or a OBDII code? Lots of good info chasing emissions issues on E46Fanatics. You may want to do a smoke test.
    George Roffe
    98 M Roadster
    01 325iT


  5. #5
    Join Date
    Oct 2018
    Location
    Franklin,TN
    Posts
    19
    My Cars
    1997 Z3 roadster
    I appreciate the feedback. This forum is very informative. I have heard a lot about this smoke test not exactly how to do it. I understand how to build a smoke generator just not how to use it.

  6. #6
    Join Date
    Feb 2017
    Location
    Suburbadelphia, PA
    Posts
    458
    My Cars
    1997 Z3 2.8 Roadster
    I'm glad we have this forum, so I'm not sitting here wondering if Code 420 isn't some pot-smoker joke I'm too old to recognize.

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