GM Service Manual Online
For 1990-2009 cars only
Battery Voltage: The scan tool displays the current state of the battery in volts.

Horn Relay: The scan tool displays On/Off to indicate the current state of the horn as commanded by the body control module (BCM).

Horn Relay Input: The scan tool displays Active/Inactive to indicate the status of the horn relay input as commanded by the body control module (BCM).