@Tauseef
Salam, How are you?
The ECU uses the O2 sensor to regulate fuel mixture known as known as the fuel "Feed control loop". Taking signals from the O2 sensor the ecu responds by changing the mixture. The O2 sensor generates a small voltage 0.9 volts when the fuel mixture is rich or the exhaust gases register richthe ECU reacts by leaning out the mixture and 0.2volts for being lean and the ecu responds by enriching the mixture. and when the fuel mixture at its optimum it registers .45volts that mean the mixture is 14.7 to 1. This is the optimum fuel air mixture.
And when the O2 sensor is missing it registers as if the engine is running lean and enrichens the mixture for the protection of the engine from pinging or knocking or detonation all being the same.