I replaced all of the O2 sensors when I first saw that "heater issue" and it was close to 100k. I was getting no "rich" code at that point.
When this issue along with a new non-OEM purge valve (solenoid issue) gave me Service light I replaced the purge valve with an OEM and replaced the new pre and post cat sensors (under Bosh 1 year warrantee).
when I pulled the 1 month old post sensor it looked sort of "charred" and I thought I found my issue - that it was defective, but the light/code returned.
also this morning, as the car warmed up (20 degree day), I thought I could hear a faint almost siren sound, cycling, almost like a scream ("help me")
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THANKS!