Senor Code H02S12 - 2001 Monte Carlo

Anybody have an idea what this means? The print out from AutoZone says:
1 - Oxygen sensor defective 2 - Poor connection at oxygen sensor 3 - Check circuit-fuse
The car has the 3.8 engine (if it makes a difference), and there are 2 O2 sensors on either side of the cat (the cat was replaced 15 months ago, at about 120K miles). Does this code indicate which of the two O2 sensors needs to be replaced?
Any info is much appreciated!
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