Circuit/System Description
WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The high beam headlamps are controlled by the BCM through the high beam relay. The relay is supplied battery voltage and is energized when the BCM grounds the low side drive control circuit. The flash to pass switch signal circuit is referenced from battery voltage by the BCM and when the switch is activated the signal circuit is grounded, and the BCM determines the switch is active when the signal circuit voltage is low.