Body Control Module (BCM)

Rear Defog Output: The scan tool displays On/Off. When the rear window defogger switch is depressed, the HVAC control module sends a class 2 message to the BCM to enable the rear defogger relay. The BCM energizes the rear defogger relay by grounding the control circuit of the rear defogger relay, which the scan tool displays as On.

HVAC Control Module

Rear Defog Switch: The scan tool displays On/Off. When the rear window defogger switch is depressed, the scan tool will momentarily display On.