o2 sensors can throw a code for catalyist efficency below threshold (is that what your throwing).

you can get universal cats from autozone, carquest, advance etc etc for about $75-100. You will just have to weld it in then or use clamps. At my work when a car has a bad cat hardly ever do we replace it with OEM. Why bother when you can get a universal, weld it in and save the customer 200-400$ and perform the same?