CUSTOMER CONCERN The 12-volt charging system is inoperative and DTCs P0AC4, U0293, and U1817 are stored. CAUSE The Hybrid Powertrain Control Module would not communicate even though its power and ground circuits were present, DLC terminals 6 and 14 measured 60 ohms, and other high-speed GMLAN modules communicated normally. Testing confirmed an internal HPCM/Starter Generator Control Module failure. CORRECTION Remove and replace the Hybrid Powertrain Control Module/Starter Gen