Conditions for Running the DTC
WARNING: This page is about a different car, the 2019 Chevrolet Malibu. However, it is still accessible from the selected car via links, so may be relevant.
P305B
The control module ignition voltage signal is valid, with the ignition OFF/Vehicle OFF.
P305C
The control module ignition voltage signal is valid, with the ignition ON/Vehicle in Service Mode.