Diagnostic Aids
WARNING: This page is about a different car, the 2009 GMC Sierra and 2009 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Many controllers such as the power inverter module (PIM), transmission control module (TCM), and inflatable restraint sensing and diagnostic module (SDM) will set a DTC for a problem with the Run and Crank/On and Start Power Voltage circuit. Confirm that they do not have DTCs before only investigating the SDGM.