You need to turn off the "Automatic Transition" car stereo setting.
On the factory stereo, press the INFO button -> Select "Screen Setting" -> Turn off "Automatic transition from audio/air conditioner to navigation."
This applies to LEX3, LEX3L, LEXGS, LEXGX, LEXSC, LEX4, LEX5, and LEX5LS VLine / VLite models and compatible Lexus and Toyota stereos.
On the factory stereo, press the INFO button -> Select "Screen Setting" -> Turn off "Automatic transition from audio/air conditioner to navigation."
This applies to LEX3, LEX3L, LEXGS, LEXGX, LEXSC, LEX4, LEX5, and LEX5LS VLine / VLite models and compatible Lexus and Toyota stereos.