Contour Enthusiasts Group Archives Forums General General Why does the bank 1 pre-cat fail?

For those with the V6...

It seems that the bank 1 (aka firewall-side) pre-cat seems to be a weak point on the car. Many people seem to get the dreaded P0420 (Catalyst System Efficiency below Limit - Bank No 1). But the bank 2 (aka radiator-side) pre-cat doesn't seem to be as predominant.

NOTE: If you search for "420" in the Troubleshooting Forum, there are ~ 275 hits, whereas if you search for "430" there are ~ 89 hits.

Does anyone have a theory on why the bank 1 pre-cats are failing much more (as opposed to the bank 2 pre-cats)?

Is this a chemical failure? That is, is the catalyst loosing its inherent ability to "catalyze" over time (possibly because of the higher temperatures that build on on the firewall). My understanding of a catalyst is that "theoretically" it should last forever.

Or is this a mechanical failure? That is, is the pre-cat crumbling or falling apart? If so, what is causing this and why only the bank 1 pre-cat?

Or is there some other reason that the bank 1 pre-cat is failing (e.g., bank 1 design vs. bank 2 design)?

Thanks ahead of time for any and all responses.