2002 Buick Century Service Engine Soon Light

I have a 2002 Buick Century, 3.1L with 149,000. About a week ago the Service Engine Soon Light came on and the code indicate the Front Oxygen Sensor, which I replaced. About a day and a half later, the light came back on and indicated the oxygen sensor again. I cleared the codes by disconnecting the battery and let the car sit for a couple days. Yesterday I reconnected the battery, started the car and the light was not on. On my way in to work this morning the light came back on. What else might be causing the light to come on cause the ECM to show an oxygen sensor issue? The car is running fine otherwise, but I hate looking at that orange light. Thanks for your help!