The Attenuation (ATT) function is designed to mute the car stereo when you receive a telephone call. If ATT is displayed but there is no incoming phone call being received or no cell phone is installed in the vehicle, there may be a problem with the installation of the car stereo.
NOTE: We recommended that you contact a qualified installer to check the installation.
If the issue is still unresolved, service may be required. Begin the procedure to send your Sony product into a Sony facility to be repaired.