O2 Sensor Circuit (Bank 2, Sensor 3)

Sensor 3 is the third O2 sensor in the exhaust stream on Bank 2, typically located downstream of the second catalytic converter, common on trucks and large V8 engines.

No, most vehicles have only Sensor 1 (upstream) and Sensor 2 (downstream). Sensor 3 is found on vehicles with dual catalytic converters per bank.

Yes, any O2 sensor code will cause an emissions test failure due to the illuminated Check Engine Light.

The OBD II regulation requires four separate detections for an oxygen sensor (Title 13 CCR 1968.2, section (e)(7.2)): deterioration in voltage, response rate or amplitude that would push emissions past 1.5 times the FTP standards; loss of circuit continuity; out-of-range values; and the case where the sensor has degraded enough that the fuel system stops using it and falls back to open loop. A sensor can therefore set a code while still producing a signal that looks plausible on a scan tool. This is the threshold the monitor is designed around, not a description of your specific fault — the regulation says what the system must detect, not how to find it on your vehicle.