Originally Posted by Deansbimmer

If the car runs well with no issues and no other codes, then I can almost guarantee the code for catalyst efficiency will come back unless you replace the cat. That code comes up when the DME does not see adequate cleaning of the exhaust stream when comparing the pre cat o2 sensor readings to the post cat o2 sensor readings. Changing all of those other parts would be good maintenance and may help increase your fuel mileage and overall efficiency but it won't get rid of a bad cat code.

I'm in fact replacing my bank 2 catalyst in my '02 4.6iS this weekend due to the exact same code. I've had the code showing for over a year but I got away with it during last year's inspection when I cleared the codes, drove it just long enough to get 4 out of 5 ready monitors, and it passed OK. This year the cat is obviously worse as I couldn't get more than 10 miles after clearing codes before the code came back.

I purchased a replacement cat on eBay from an 03 4.6is, but the seller wasn't aware that it was a new OEM replacement cat made in 2011. So, bonus for me even though it's a bank 1 assembly. The catalysts themselves are the same from either bank, so I've got it cut out of the bank 1 piping, and will install it this weekend.

Usually you think of cats lasting half a million miles, but many BMW's in the early 2000's in particular have been known to kill them quite quickly, to the point that BMW was forced to place an extended warranty on them by the EPA. Some last, some don't. My point in saying that is to recommend that you not assume "it couldn't be" the cat and end up spending your money and sanity chasing other 'maybe' solutions.

For the record, I own a BMW shop. I replaced all the same sensors and parts you are thinking of doing, and much more...didn't make a difference at all but felt good knowing that they were fresh.