Eugene, I'd be guessing but it sounds like it's be bank 2 and post cat sensor...
But, 02 sensor codes often seem to come about because of other things pretty often...though with only one 02 code (assuming the heater is built into sensor) that might be more reliable.
I do know that cats on an older 750 have heaters independent of the sensor, but don't recall that on an e36.
I don't want to beg, but please, please come to a show sometime!
In NYC Fri, Sept. 30, 8 p.m. at Broadway Comedy Club! Sat, Oct. 8, 6 p.m. at Greenwich Village Comedy Club.
Mangofy your E46!