How to Obtain the Audio Unit Serial Number

To obtain the audio unit serial number on a vehicle, do following:

NOTE:

This procedure can only be done when the power has been disconnected from the audio unit, and the audio unit displays CODE when the audio unit is turned on.
If the audio unit does not display CODE when turned on, remove the No. B1 fuse (15A) from the under-dash fuse/relay box for 1 minute, then reinstall the fuse.

Turn the ignition switch to ON (II).
Make sure the audio system is turned off.
Press and hold the preset No. 1 and No. 6 buttons.
While holding the buttons, press the PWR button to on.

Fig 1: Identifying PWR Button, No. 1 And No. 6 Buttons
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Release the buttons, and the self-diagnostic begins (for 20 seconds).
The display shows an 8 digit number (example 12345678).

Fig 2: Screen Display - Digit Number
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Use all 8 numbers as the serial number when using the Interactive Network (iN) to retrieve the 5 digit anti-theft code.
To end the self-diagnostic function, turn the audio unit off, or turn the ignition switch to LOCK (0), or it will end by itself if no operation is done for 20 seconds.