Circuit/System Verification
WARNING: This page is about a different car, the 2009 GMC Yukon and 2009 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.
Verify that DTCs P0787, P0973, P0976, P2764 have not set, if so, diagnose first. With a scan tool, command the TCC Solenoid valve ON and OFF.