Oxygen Sensor

1. Powertrain Control Module (PCM)
2. Throttle Position (TP) sensor
3. Mass Air Flow (MAF) sensor
4. Intake Air Temperature (IAT) sensor
5. Idle Air Control (IAC) valve
6. Engine Coolant Temperature (ECT) sensor
7. Heated Oxygen Sensor (HO2S)
8. Camshaft Position (CMP) sensor
9. Knock Sensor (KS)
10. Vehicle Speed Sensor (VSS)
11. Crankshaft Position (CKP) sensor
12. Fuel Injector
13. Coolant Temperature Sensor (CTS)
14. Exhaust Gas Recirculation (EGR)
15. Manifold Absolute Pressure (MAP)

Source: FreeAutoMechanic.com/car-engine-sensors.html

Oxygen Sensor

Measures the percentage of oxygen in the exhaust, and tells the computer whether the fuel/air mixture is too rich or too lean.

HO 2S

The heated oxygen sensor is used by the powertrain control module to measure the amount of oxygen in the exhaust. The PCM uses this data to control the air fuel mixture in the engine. The PCM sends a bias voltage of approximately 450 mV to the oxygen sensor. At operating temperature the oxygen sensor signal varies between 0 and 1,000 mV. When the mixture is rich the oxygen content is low and the voltage signal will remain on the high side of the 450 mV mid-range. When the mixture is lean the oxygen content is high and the voltage signal will remain on the low side below the 450 mV mid-range.