I was looking at 02 simulators on urd's website and it says this.
Be cautious of O2 sims that replace the rear O2 sensor with a falsely gererated signal.
Toyota started using a wideband type O2 sensor (air/fuel ratio) in the front position for better engine control. These wideband type sensors need to be recalibrated from time to time by the ECU. The ECU uses the rear sensors for this recalibration process. The ECU cannot properly recalibrate the wideband sensor using a falsely generated signal.