So for the past month, my '01 limited was running like crap and throwing these codes: 0132, 0152, 0135, 0141, 0302, 0155 and 0161. This past Monday, Feb. 3, I replaced the upstream O2's in bank 1 sensor 1 & bank 2 sensor 1 with NTK #'s 23151 & 23506. I cleared the codes and reset the ECU. It ran better and still runs better than it did for but on Wed., Feb. 5, these codes returned: 0135, 0141,0155 and 0161. Have the 2 upstream 02's I replaced gone bad? Should I replace the downstream 02's now or do I need to replace all (4) 02's at the same time?

 

I am looking at the first set codes you had and the second set you have now.
Have you gone over the wiring to the O2 sensors?
First though the second set of codes is all heater related.
I had a CEL when I first bought my '00.
With CA Emissions so basically the same as your Jeep.
Anyway, it was P0135 if I recall correctly.
There is a fuse, small regular one not the maxi ones, in the PDC (fuse box in the engine compartment) for the heaters.
Mine was blown. Replaced it and all was well.
Which actually surprised me cause I figured the fuse blew for a reason, cured the symptom and not the disease, but
since it never blew again nothing to diagnose so....
Anyway give all those a quick check, cause I can't remember which one, and go over your O2 wiring if that does not pan out.

 

I never thought of the fuse. I'll definitely check that.