Circuit/System Description
WARNING: This page is about a different car, the 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The 4 low indicator circuit consists of a light emitting diode (LED), a LED feed circuit and a LED control circuit. The indicator dimming control circuit is the LED feed circuit and continuously supplies voltage to the 2 High, 4 High and 4 Low LEDs. When the 4 Low mode has been selected by the driver, the transfer case shift control module (TCCM) provides a ground through the 4 Low indicator control circuit illuminating the LED. The TCCM tests the 4 Low indicator circuit for unexpected voltage by monitoring the B+ supplied by the BCM on the indicator dimming control circuit by grounding the 4 Low indicator control circuit for 2 seconds during the bulb test at key ON.