My check engine light came on today and I took it to Advanced Auto Parts for a diagnostic check. It came back as Code PO141; Bank 1 Sensor 2, 02 sensor heater. Does anyone know if this is the Upstream or Downstream? I have a 2002 Lexus IS 300 with 67,720 miles on it and the guy said I shouldn't have a problem with it because it's supposed to last for up-to 100,000 miles. Does anyone know if this is true?

It is the sensor after the cat converter. They normally last for over 100K, but there is no guarantee. Replace it with one matched to your vehicle with your VIN at a Lexus parts department. You don't have to buy it there, but get the correct part number there.