Here are some basic knowledge about 02 sensors. There are 3 sensors on the ES300: Bank 1 sensor 1, Bank 2 sensor 1 and Bank 2 sensor 2.
Location of the sensors: Two sensors on the exhuast manifolds and one more behind the cat converter.
Which one is which? Bank 1 sensor 1 is the located by the fire wall, Bank 2 sensor 1 is the one on the front.
What are their jobs? Bank 1 sensor 1 and Bank 2 sensor 1 called the A/F(air/fuel) sensor. It measures the amount of air/fuel coming out of the exhuast manifold. These A/F sensor will send the signals your main ECU, The ECU will control the injectors(speed them up or slow them down). 02 sensor located bethind the cat converter, it measure the performance of your cat converter.
One last thing, Never trust anyone at autozone diagnost your vehicle. They are not certified and never have any training. Please spend some money have qualified tech work on your Lexus. I hope I clear something up.
JPI