Circuit/System Description
WARNING: This page is about a different car, the 2008 GMC Yukon and 2008 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.
The hybrid powertrain control module (HPCM) monitors the state of the 4WD range signal message, if equipped, over the GMLAN communication bus. The HPCM uses this message to determine motor torque required and transmission shifting, there are no external circuits involved.