2022-2025 Audi 48V MHEV Electrical System Fault TSB

Audi has released Technical Service Bulletin (TSB) 2073284/1, dated March 9, 2024, to address an "Electrical system fault" that may appear in the instrument cluster of certain 2022-2025 Audi 48V Mild Hybrid Electric Vehicle (MHEV) models. This bulletin specifically clarifies the diagnosis and repair strategy for diagnostic trouble code (DTC) U046900 and related issues. Owners of an Audi Q8 48V MHEV electrical fault should be aware of this information.

Symptoms

Owners may observe an "Electrical system fault" message displayed in the instrument cluster. If the vehicle continues to be driven with this fault, there is a risk that the vehicle could lose power as the battery becomes excessively discharged. This indicates a potential issue with the 48V MHEV electrical system.

Fault Codes / DTCs

Workshop technicians may find one or more of the following diagnostic trouble codes (DTCs) stored in the vehicle's Engine Electronics (-J623-) or Brake Electronics (-J104-) modules:

• Engine Electronics, 0001:
  • U046900: Lost Communication with Starter/Generator Control Module - Symptom: 34763
  • U002900: Sensor/Hybrid CAN No Communication
  • U002800: Sensor/Hybrid CAN Faulty
• Brake Electronics, 0003:
  • C054A00: Brake Servo Pressure Sensor
  • C11EC04: Brake Servo Pressure Sensor

Technical Background

Audi's technical background for TSB 2073284/1 explains that replacing the 48V Starter/Generator will not resolve the problem associated with DTC U046900. The code "U046900: Lost Communication with Starter/Generator Control Module – symptom: 34763" is typically stored due to another electrical system problem affecting the vehicle's CAN bus. The Starter/Generator itself is not the root cause of the concern. This condition is often documented in the expanded ambient conditions of the event memory, specifically showing the value "Starter generator, actual mode 48V = 8".

Diagnosis and Repair Procedure Summary

To properly address the Audi Q8 48V MHEV electrical fault, technicians must focus on diagnosing and processing the sensor faults within the Engine Electronics and Brake Electronics. These sensor faults are the underlying cause. A potential fault in these sensors can disrupt the vehicle's data bus system, leading the Engine Electronics to command the 48V Starter/Generator to freewheel. This action prevents the battery from being charged, resulting in the observed electrical system faults.

Important Warnings

Owners and technicians should be aware that replacing the 48V Starter/Generator will not fix this problem. The issue stems from other electrical system problems on the vehicle's CAN bus, specifically related to sensor faults. This Technical Service Bulletin is for informational purposes only and is not applicable to any Audi Warranty.

Owner Action

If your 2022-2025 Audi 48V MHEV vehicle displays an "Electrical system fault" message or if you experience symptoms like power loss, it is crucial to have your vehicle inspected by an authorized Audi service center. Inform them about TSB 2073284/1 to ensure they follow the correct diagnostic procedure, focusing on sensor faults rather than immediately replacing the 48V Starter/Generator.

Source: NHTSA ID: 10251623