We have tried a few suppliers of aftermarket cats, and
will do so no longer on OBD-2 cars.

The code is actually a "catalytic convertor efficiency" discrepency.

This parameter is set by the factory, and cannot be altered.
We have seen a large number of 210 cars with failed cats, some 202's.
BMW 740's seem prone, as well. Very often the substrate in the cat breaks up, and rattles annoyingly at idle.

The aftermarket cats we tried were replaced with factory units, and the
problem was cured. Lesson learned.

Pre-96 cars we have used the aftermarket cats with success.
(1 O2 sensor per bank, vs. 2 per bank in OBD-2 cars).
Less stringent monitoring.
These are not the generic, cut-the-pipe-and-weld-it-in type cats.
We use those only on 80's Euro stuff where there is no real option.

We have emissions testing, and the annual state inspection can not be performed on a car with check engine light on, or readiness tests not having been met.

__________________
Todd Haven
Parts Manager
MPH Automotive
Houston,TX