Where is the B1S2 heater circuit located on this vehicle? on 2001 Chevrolet Blazer

Got a code P0141 and a P0128(which i understand is most likely the thermostat. Which 02 sensor is the B1S2 sensor on the 2001 Chev blazer?

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2 answers
From the fuse box fuse to the o2 sensor then to a ground, usually means bad o2 sensor.
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