We have done 3 exhaust systems for same issues. They set NOX related codes, but all we have removed have had evidence of cracked particle filters. It's a PITA getting approval based on NOX codes and getting paid for all the non SLTS diagnosis is no walk in the park either. Next one that comes in we are going to remove the tailpipe and have a peek in the back of that bad boy, then it will be presented as soot in tailpipe, so much easier to get approval for a cracked DPF.