Circuit/System Description
WARNING: This page is about a different car, the 2010 GMC Sierra and 2010 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The Neutral indicator circuit consists of a light emitting diode (LED) feed circuit, a LED and a LED control circuit. The Ignition 1 voltage circuit is the LED feed circuit and continuously supplies B+ to the Neutral LED. When the Neutral mode has been selected by the driver, the transfer case shift control module (TCCM) provides a ground through the Neutral indicator control circuit illuminating the LED.
The TCCM tests the Neutral indicator circuit for unexpected voltage by monitoring the B+ supplied by the BCM on the Ignition 1 voltage circuit by grounding the Neutral indicator control circuit for 2 seconds during the Bulb Test at key ON.