Our X5 just failed the Emissions Test - Opinions needed!

[msammy]

OK, so we were just handed our CT State emissions test form with big FAILED warning on it. Our 2002 X5 (original owners, VERY well maintained) has only 158K miles with many more miles left in her. OK, so I grabbed my phone, plugged in the OBD2 adapter and connected the Carly app to see what's going on. I'm reading the following code:

"Catalyst Efficience main cat. Bank 2" Code: 0000EA

OK, cool, also scanned with the Actron Pocket scanner and getting OBD code P0430.

I've searched this forum from top to bottom for similar codes, etc. and although finding a great deal of info, unfortunately each thread dies with no conclusive results.

So, from what I've gleaned from the various non-conclusive threads is this plan in this order:

Starting from the front of the X5 moving back:
o Replace air filter
o Clean MAF with MAF cleaner
o STOP, clear codes and see if OBD code comes back

--If so--
o Inspect and replace DISA valve if necessary
o STOP, clear codes and see if OBD code comes back

--If so--
o Replace both pre-CAT 02 Sensors
o STOP, clear codes and see if OBD code comes back

--If so--
o Replace both post-CAT 02 Sensors
o STOP, clear codes and see if OBD code comes back

--If so--
o Consider replacing both CATS at major expense or throw in the towel and part the old X5 out on Ebay/Internet.

So, recommendations/suggestions will be greatly appreciated. Our X5 has been part of the family for 15+ years with lots of memories but we don't want to spend more than She's worth in parts to keep her going! Maybe work backwards from the rear CAT sensors then forward would be a better approach???