Circuit/System Description
WARNING: This page is about a different car, the 2012 GMC Yukon XL, 2012 GMC Yukon, 2012 Chevrolet Tahoe, and 2012 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
The 4 High 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, Auto 4WD, and 4 High LEDs. When the 4 High mode has been selected by the driver, the transfer case shift control module (TCCM) provides a ground through the 4 High indicator control circuit illuminating the LED. The TCCM tests the 4 High indicator circuit for unexpected voltage by monitoring the B+ supplied by the BCM on the indicator dimming control circuit by grounding the 4 High indicator control circuit for 2 seconds during the bulb test at key ON.