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  1. SM (2001-2006) Santa Fe
    2003 Santa Fe, 2.4 4 cyl. I got a P0421 code recently, so I thought I'd take a look at the cat and the O2 sensors to see what was going on, if they could be cleaned, etc. This is what I found: Looks like the top substrate has completely melted. Downstream O2 sensor also looks heat...