Which sensor is bank 1 3 on 2000 Chevy s10 with 4.3?

Bank 1, sensor 3 on a 2000 Chevy S10 with a 4.3-liter engine is the oxygen sensor located on the exhaust manifold of the engine. It is mounted near the rear of the engine, closest to the firewall, and is positioned downstream of the catalytic converter. The purpose of this sensor is to monitor the amount of oxygen in the exhaust gases and provide feedback to the engine's computer (ECM) to adjust the air-fuel mixture.