The O2 (Oxygen Sensor) is responsible for monitoring the level of oxygen in the exhaust gas of each bank. The air-fuel mixture should be close to the ideal ratio or stoichiometric mixture so that the TWC (Three Way Catalyst) works in the best way. The output voltage of the oxygen sensor is changing according to the approximation of the stoichiometric ratio.
The ECM (Engine Control module) adapts the time in which the fuel is injected so that, in this way, the air-fuel ratio is ideal. The oxygen sensor has a voltage between 0.1 to 0.9 volts, which are in response to the oxygen in the exhaust gas.
The Engine Control Module (ECM) determines that the O2 sensor voltage is high when the mixture is rich, and the voltage is low when the mixture is poor. In the same way, it determines this tension, so that the injector increases or reduces its width according to the air-fuel ratio. If the ECM (Engine Control module) detects that the Oxygen Sensor voltage goes down for more than 2 minutes, the DTC diagnostic code P0136 is set.