Diagnostic Aids
WARNING: This page is about a different car, the 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
A scan tool can be used to command the GEN L-Terminal circuit ON to 85% and OFF to 14% while the engine is running. Typical voltage values for the charge indicator control circuit are 4.3 V at 85% and 0.85 V at 14%.