CPE CAT failure - CEL code P0421

I got the CEL again. Guess I'll take another look at the O2 sensor. But I am going to call CPE nevertheless. Maybe the upstream CAT is not working properly.
 
Spoke to Josh about this, he said to contact Jordan and find out about a way to clean out the CAT...

Failing that, there's the resistor trick, replacement CAT sent to me, or send off my DP to get a new CAT welded in.
 
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