Conditions for Setting the DTC
WARNING: This page is about a different car, the 2009 GMC Yukon, 2009 Chevrolet Tahoe, 2009 Chevrolet Suburban, and 2009 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
The voltage is above 18.5 volts or below 10.5 volts for 15 seconds.