For 1990-2009 cars

### Body Control Module (BCM)

Battery Voltage Signal: The scan tool displays Volts. This is the current battery voltage available at the body control module (BCM).
Rear Defog Relay Cmd.: The scan tool displays On/Off. When the rear window defogger switch is depressed, the body control module energizes the Rear Window Defogger relay by suppling battery voltage to the control circuit of the relay. When the switch is depressed the scan tool will display On.
Rear Defog Switch: The scan tool displays Off /On. When the rear window defogger switch is depressed, the HVAC control module sends a message over Low Speed GMLAN to the BCM. When the switch is depressed the scan tool will display On.