All 99+ models are equipped with two oxygen sensors. One upstream Oxygen sensor, and one downstream Oxygen sensor. The upstream oxygen sensor is mounted in the exhaust before the catalytic converter, and the downstream one is mounted in the exhaust after the catalytic converter. There is some great info on how to check and replace the Oxygen Sensor [http://www.automotiveforums.com/t672110-oxygen_sensor_99_grand_am__testing_and_replacement.html|right here.] Hope this helps, good luck.
[image|171111]
[image|171110]