Inspection Procedure 6: The Sound Of External Input Are Not Played: Notes
WARNING: This page is about a different car, the 2008 Mitsubishi Lancer. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION:
Before replacing the ECU, ensure that the power supply circuit, the ground circuit and the communication circuit are normal.
Fig 1: Audio And Video Adapter Communication Circuit Diagram