The Oxygen Sensor 2 (HO2S) is located at the back of the Catalytic Converter (TWC), and its function is to monitor the amount of oxygen in the exhaust gas of each bank. For the Three-Way Catalyst (TWC) can work properly and be most efficient, the air/fuel mixture must be the closest to the stoichiometric ratio. Besides, the oxygen sensor (HO2S) output voltage can change suddenly as it approaches the stoichiometric ratio.
The Engine Control Module (ECM) adapts the time the fuel is injected, so the air/fuel ratio can be either ideal or stoichiometric. The voltage generated by HO2S is 0.1 to 0.9 volts depending on the oxygen in the exhaust. If the oxygen in the exhaust increases, the air/fuel ratio is poor, this happens when the oxygen sensor voltage is less than 0.45 volts. If the oxygen in the exhaust gas diminishes, the air/fuel ratio will be excellent. The Engine Control Module (ECM) interprets excellent when the oxygen sensor voltage is above 0.45 volts.