Please school me on the operation of a 02 sensor

[billschroeder5842]

I got some weird codes (13) on my 02 sensor so please school me in the operation of our three-wire O2 sensors system. I get that the two wire give signals to the CCM to help decide open/closed loop and the third wire is for the "heat element."

Does the heat element heat up on key forward or engine started and running? Does the heat element go off after a point? Is that triggered by temperature or by timing? What would cause a SES light to come on briefly, throw a code, then go out? Does the addition of headers (I just added them a few weeks ago) cause a reading difference even after a top notch tune?

I not super worried (I'll just swap in a new 02) I'm just curious how the system works and what triggers what.