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...