WARNING: This page is about a different car, the 2010 Pontiac G5 and 2010 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.
Battery Voltage Signal - PSCM
Circuit
Short to Ground
Open
Short to Voltage
Operating Conditions:
Ignition ON, Engine OFF. Parameter Normal Value:
12.60 Volts