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p0421

  1. Do It Yourself Catalytic Converter Replacement?

    Mazda3 (Axela)
    So it turns out the P0421 code I have been getting on my 2010 Mazda 3 2.0l is actually a faulty catalytic converter. Replaced all of the O2 sensors as well as got an exhaust leak welded up. The muffler shop said the catalytic converter looked very rusty. The guy mentioned off the top of his head...
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