1997 Ford Taurus Oxygen Sensors

All four of these sensors have been replaced and yet after the computer is cleared using the correct device, the light comes back on in a short period of time. The sensor that the computer code identifies as not operating properly changes among the sensors after error is cleared. The code in the computer has never been updated. Is there a place one might get a code update for this vehicle. After replacing all four sensors, one would not expect to continue getting these type of readings.

Thanks