Need help w/Heated Oxygen Sensor

My "Check Engine" indicator lighted up on my 2001 GS300. The code reader indicated "HO2S Heater Circuit Malfunction Bank 2 Sensor 2". Talking to a Lexus Technician, he said it was the O2 sensor after the Cat. Converter. I assume it's the heater part of the sensor that malfunctioned. To change it, the connector is located under the passenger seat. I looked under the seat and found three connectors that I can see. a Yellow, Gray and White. Anyone know which one, if any of them, is the correct one and how do I disconnect it? also, am I on the right track? How hard is it to replace the sensor and any tricks I need to know?

I see four wires going to the sensor: white, blue and 2 black wires. Can I assume the 2 black are the heater wires? If anyone has a manual, I'sd appreciate an answer.

I have A 2001 GS300 with 33000 miles. The Lexus technician said the sensor failure is more a matter of time rather than miles. It heats up to 700 degrees.

Thanks

Dan