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 the commanded state of the horn relay. The scan tool displays ON when the BCM applies ground to the horn relay to activate the horn(s).

Horn Relay Input: The scan tool displays the state of the horn relay. The scan tool displays ACTIVE when the BCM senses that the horn relay is being commanded ON by the relay coil circuit being grounded.