Communication and Hosted Diagnostics
WARNING: This page is about a different car, the 2012 Chevrolet Volt. However, it is still accessible from the selected car via links, so may be relevant.
The 14V power module has internal diagnostic tests that run at both power-up and during operation. All DTCs from the 14V power module are reported to and hosted by the hybrid powertrain control module. The 14V power module only communicates with the hybrid powertrain control module and only over serial data.