OBD2 code 0161 explanation

Pulled code 0161 from my reader. "downstream heated O2 sensor heater circuit fault".
My question is: does this mean that the O2 sensor has failed or the circuit
powering it has failed. The code is intermittant cuz I can reset it and it sometimes does not come back for a while and I see no affect with engine performance when the ses light is on.
Does anyone have prior experience with this code so I don't go changing something that doesn't need changing?
thanks, Chris
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No, it doesn't mean that the sensor has failed. It means that the circuit for heater inside the O2 sensor has failed.

O2 heater monitors run only under certain circumstances.

Test the circuit as was intended by the manufacturer. The code doesn't necessarily mean to replace the sensor, there could be a wiring problem, a bad ground, a bad comparator circuit in the PCM or yes, a bad sensor.
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