Toyota Repair: 2000 Toyota Sienna Oxygen Sensor, powertrain warranty, engine warranty

Question
I was told that I need the Bank 1 sensor1 front California emission Oxygen Sensor replaced on my 2000 Toyota Sienna.  I was wondering if this is covered under the Engine warranty (5yrs 60,000 miles)?  I've been trying to find the replacement part online at expressautoparts.com but I can't tell which one it is based on the descriptions given.  I tried their cust. service but they still haven't gotten back to me.  Could you please direct me to the correct replacement part?  Do you know if it should be covered under the engine warranty?  I keep getting the run-around from my Toyota dealer.  
THank you for your help.

Answer
The bank 1 sensor 1 is located on the right side of the engine(standing in front of the car) it's the one to the rear next to the firewall, it's located on the exhaust manifold.
The federal emission control warranty period is 3yr/36,000 miles, the california emission control warranty is 3yr/50,000 miles whichever comes first. It is not considered engine(powertrain) warranty.