Here's another CEL question, but this one has got a little twist.

Got a CEL, took it to the shop, they did "full" diagnostic and returned the code for Catalytic Converter. I don't remember the code exactly, but I looked it up when I was at home, and sure enough it was Catalytic Converter.

Ok, so I need a new Cat and will probably just buy one at autozone for $150 or so, and bolt it in.

But here's my actual question: How is the system getting "Catalytic Converter"? I looked in helms, and no sensor screwed into the Cat. Doesn't seem that the o2 sensors would be able to "sense" this. Would sensors on the manifold trigger Cat code due to higher back pressures? Someone help me understand. I replace parts and such, but I’m not a mechanic, so I’m still figuring out the principles behind how the stuff works.

Thanks,

William
98 Civic EX