Okay, I've asked this question before and am still confused to this day as to the proper number of cats on each year and model. So lets hope this thread will put an end to it and clear up some confusion.

I want to see some pictures to explain what people are talking about. Because when people say a set or a pair of cats I want to know which area they are talking about. The headers with cats or the down pipes with cats just before the muffler? Depending on the year, I know it varies. So let me start by showing what I have found and hopefully some one can post another picture of the 2000-2004 diagram from a repair manual and circle the O2 sensors as I have, to show them on the cats. Here is the image from a European repair manual I found for the older Boxster(97-99) showing the set up with only 1 set(pair) of cats on the down pipes just before the muffler. No cats at all on the headers as you can see. Now can someone please show me, and circle the ones for the 00-04 models? I've heard everything form 2 to 4 sensors all located on the later models years 00-04 in the headers only. If that's true, then are there still another set of sensors on the ones located on the cats connected to the down pipes for the 00-04 models?