The voltage on the oxygen (O2) sensor is based on the amount of oxygen in the exhaust. Its voltage changes between 0.1 and 0.9 volts. 0.1 volts would be a poor condition and 0.9 a rich condition.
When the circuit is closed, it is monitored by the Engine Control Module (ECM), which is responsible for establishing the amount of injected fuel. If the ECM (Engine Control Module) signals that the O2 (Oxygen Sensor) voltage is below 0.4 volts for a time of 20 seconds (although the time varies according to the model), the fault code P0150 OBD2 will be set. This code refers to bank 2.