what is wrong when codes say my fuel is running rich and oxygen sensor malfuncti on 2005 Audi A6 Quattro

i had autzone reset the codes and it hasnt happened anymore

Asked by for the 2005 Audi A6 Quattro
If one of the O2 sensors fail it could read "rich" air fuel ratio on the bank of cylinders with the failed O2 sensor. Other things can influence a rich running condition, a failed fuel pressure regulator, leaking fuel injector, bad coolant temperature switch or air flow meter.