Your vehicle has four O2 sensors. Two per bank, one before and one after converter.
Get oriented with the expressions "upstream" and "downstream". Upstream is the portion of the exhaust closest to the engine, downstream is closest to the tailpipe. Bank 1 on a transverse-mounted engine is the firewall side, bank 2 is the radiator side. Therefore, O2S12 (oxygen sensor, bank 1, sensor 2) is the downstream (post converter) sensor on the firewall side of the engine.
Before you jump into replacing any sensors, be advised that actual troubleshooting is highly recommended. Downstream sensors don't affect engine operation and don't fail very often. You might want to post your symptoms and allow more experienced eyes to double-check the diagnosis since O2 sensors usually run $50-70 (which can buy a lot of beer!).
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