2019-2025 Audi MHEV Electrical System Fault TSB

Owners of 2019-2025 Audi MHEV (Mild Hybrid Electric Vehicle) models may encounter an "Electrical system fault" message displayed in the instrument cluster. This condition, detailed in Audi Technical Service Bulletin 2073284/2, can lead to a risk of power loss if the battery becomes excessively discharged. It's crucial to understand the underlying cause of this Audi MHEV electrical fault to ensure proper diagnosis and repair.

This TSB, issued on June 5, 2024, supersedes previous bulletin Group 27 number 24-68 dated March 9, 2024. It provides updated guidance for technicians addressing these electrical system concerns.

Symptoms

If your Audi MHEV is affected, you may observe the following:

• An "Electrical system fault" message appearing in the instrument cluster.
• A potential risk of the vehicle losing power if the 48V battery becomes excessively discharged due to the fault.

Fault Codes / DTCs

Technicians diagnosing this Audi MHEV electrical fault may find one or more of the following Diagnostic Trouble Codes (DTCs) stored in the Engine Electronics (J623) or Brake Electronics (J104) control modules:

Code	Description	Module
U046900	Lost Communication with Starter/Generator Control Module – Symptom: 34763	Engine Electronics
U002900	Sensor/Hybrid CAN No Communication	Engine Electronics
U002800	Sensor/Hybrid CAN Faulty	Engine Electronics
C054A00	Brake Servo Pressure Sensor	Brake Electronics
C11EC04	Brake Servo Pressure Sensor	Brake Electronics

Diagnosis and Trigger Conditions

The presence of DTC U046900, indicating "Lost Communication with Starter/Generator Control Module – symptom: 34763", does not mean the Starter/Generator itself is faulty. Instead, this code is typically stored due to other electrical system problems on the vehicle's CAN (Controller Area Network) bus. These issues often manifest in the expanded ambient conditions of the event memory, showing a value like "Starter generator, actual mode 48V = 8".

Sensor faults in the Engine Electronics and Brake Electronics, along with communication errors, can disrupt the vehicle's data bus system. This disruption can cause the Engine Electronics to command the 48V Starter/Generator to freewheel, which prevents the battery from charging and ultimately leads to the Audi MHEV electrical fault.

Specifically, DTCs U002900 and U002800 in diagnostic address 0001 (Engine Electronics) point to potential causes such as:

• Communication connectors not being properly plugged in or fastened, including bent or widened pins, or short circuits within the wiring.
• Incorrect attempts to swap connectors, such as failing to connect vehicle ground cables.

Important Warnings

Audi explicitly states the following critical information for this issue:

• Do not replace the 48V Starter/Generator. Replacing this component will not resolve the problem, as it is not the root cause of the fault.
• If the Starter Generator (diagnostic address 00CC) cannot be reached in ODIS (Offboard Diagnostic Information System), this does not automatically mean the component is faulty.
• This Technical Service Bulletin is for informational purposes only and is not applicable to any Audi Warranty.

Repair Procedure Summary

The repair procedure focuses on identifying and rectifying the underlying sensor faults and communication errors rather than replacing the Starter/Generator. Technicians should thoroughly investigate the Engine Electronics, Brake Electronics, and the communication error faults to pinpoint the root cause.

This involves checking the communication connectors for proper seating, inspecting pins for damage (bent, widened), and looking for any short circuits in the wiring. Incorrectly connected or swapped connectors, particularly those related to vehicle ground cables, must also be addressed.

Owner Action

If your 2019-2025 Audi MHEV displays an "Electrical system fault" or you suspect an Audi MHEV electrical fault, it is recommended to schedule an appointment with an authorized Audi service center. Inform them of the symptoms you are experiencing and mention Technical Service Bulletin 2073284/2. The technicians will perform a comprehensive diagnosis to identify the specific sensor or communication issue causing the fault and implement the appropriate repair.

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Source: NHTSA ID: 11002893