Auto Parts: Oxygen Sensor, chevy avao, chevy dealer

Question
Got engine light on my 2007 Chevy Avao Sedan. My comuitor car. Tested at chevy dealer. Said you need new Oxygen sensor for fuel to oxygen mixture. Part #96418965. They're going to charge me a arm and leg. I can get this part for about $110 online. Is it easy to install and where would it go??
Thanks
Steven

Answer
    It's easy to install.  If it's the downstream sensor (most likely) it is screwed into the pipe at the back of the converter.  If it's the upstream sensor (I don't think the computer can diagnose this sensor) it is located adjacent to the joint between the manifold and the manifold pipe.  You will need an oxygen sensor socket (about $20) to remove and install the sensor.  Why isn't this covered by warranty?  Is there a lot of mileage on the car?  Warranty should cover five years and 50,000 miles.