Circuit Description
WARNING: This page is about a different car, the 2005 Toyota Sienna. However, it is still accessible from the selected car via links, so may be relevant.
The radio and navigation assy controls the volume according to the MUTE signal from the stereo component controller assy.
The MUTE signal is sent to reduce noise and a popping sound generated when switching the mode, etc.
If there is an open in the circuit, noise can be heard from the speakers when changing the sound source.
If there is a short in the circuit, even though the radio and navigation assy is normal, no sound or only an extremely small sound can be produced.