Mercedes GLE AMG 53 (2021) – No Start Due to Failed 48V Starter Generator Power Electronics Module

About This Case

Customer Complaint The customer reported that the vehicle suddenly failed to start. After multiple attempts, the 12V battery gradually discharged due to repeated starting attempts. Believing the issue was battery-related, the customer replaced the 12V battery; however, the vehicle remained completely unable to start. The customer then contacted us and booked a professional diagnostic session. Diagnostic Process Upon vehicle arrival, a comprehensive diagnostic procedure was performed using advanced Mercedes-Benz diagnostic and programming equipment. The initial inspection confirmed that the newly installed 12V battery was operating correctly. Attention was then directed to the vehicle's 48V mild-hybrid system, which plays a critical role in engine starting and energy management. Further analysis of the fault memory, live data, and system status revealed abnormal behavior within the Power Electronics Starter Alternator Module associated with the Integrated Starter Generator (ISG) system. A recurring fault code was identified: "System shutoff could not be performed." Additional testing indicated an internal failure of the module's high-voltage contactors, preventing proper power management and starter-generator operation. As part of the verification process, the module software was updated and reprogrammed to eliminate any possibility of software corruption. The fault remained active, confirming a hardware failure inside the module. Repair Procedure Performed complete system diagnostics. Evaluated 12V and 48V electrical system operation. Analyzed fault memory and live vehicle data. Updated and programmed the power electronics module as a verification procedure. Confirmed internal module failure. Replaced the faulty Power Electronics Starter Alternator Module. Programmed and commissioned the replacement unit. Performed post-repair testing and validation. Results Following replacement and programming of the Power Electronics Starter Alternator Module, the 48V system returned to normal operation. The Integrated Starter Generator resumed proper functionality, fault codes were eliminated, and the vehicle started immediately without issues. The vehicle was successfully returned to the customer with all systems operating within manufacturer specifications. Services Performed ✔ Advanced Mercedes-Benz Diagnostics ✔ 48V Mild Hybrid System Diagnostics ✔ ISG (Integrated Starter Generator) Diagnostics ✔ Power Electronics Module Programming ✔ Control Module Replacement ✔ Mercedes-Benz Coding & Programming ✔ Post-Repair Validation Testing