Heated Oxygen Sensor (HO2S)

Oxygen sensor detects oxygen content of exhaust gases and sends signal to PCM, which varies air/fuel ratio to maintain a 14.7:1 (optimum) ratio under most conditions. This ratio is most efficient for combustion and Three-Way Catalytic Converter (TWC) operation. O2S has an internal heater to stabilize sensor output. Each vehicle has at least 2 Heated Oxygen Sensors (HO2S). There is a primary HO2S-1 mounted in front of TWC and a secondary HO2S-2 behind or inside TWC. Deterioration of primary HO2S-1 can be evaluated by its feedback period. When feedback period exceeds a preset value, during stable driving conditions, primary HO2S-1 is considered deteriorated and PCM sets a DTC. On some models, the front HO2S is an air/fuel ratio sensor. See Air/Fuel Ratio Sensor (A/F Sensor) .