2021-2023 Audi 48V Electrical System Malfunction DTC U046900 TSB

Audi has released Technical Service Bulletin (TSB) 2058831/13, superseding previous bulletin 24-65, to address an Audi 48V electrical system malfunction affecting various 2021-2023 models. This bulletin provides comprehensive diagnostic and repair information for situations where a warning message is displayed on the instrument cluster and Diagnostic Trouble Code (DTC) U046900 is stored in the Engine Control Module (ECM).

Symptoms of an Audi 48V Electrical System Malfunction

Owners of affected Audi vehicles may notice the following indicators of an Audi 48V electrical system malfunction:

• The instrument cluster displays the message: "Electrical system: Malfunction. See owner's manual".
• A yellow or red battery warning symbol illuminates on the instrument cluster.
• The German warning message "Bordnetz: Störung! Bitte Service aufsuchen" (Electrical system: Malfunction! Please seek service) may also appear.

Fault Codes / DTCs

When diagnosing an Audi 48V electrical system malfunction, technicians may find specific Diagnostic Trouble Codes (DTCs) stored in the vehicle's control modules. The primary DTC associated with this issue is:

| Code | Description | Module | | :--- | :---------- | | U046900 | Invalid data received from starter/generator control module (symptom 36564) | ECM (J623) or Gateway (J533) |

If, after initial diagnostic steps, another event memory entry is shown in ODIS, the following DTC may also be present:

| Code | Description | Module | | :--- | :---------- | | B200096 | Faulty control module | Starter-alternator |

Important Warnings for Owners and Technicians

Audi has issued specific warnings regarding the diagnosis and repair of this Audi 48V electrical system malfunction:

• "The DTC and symptom must match for this TSB to apply."
• "If the listed DTC is not stored in the test plan, then the generator is not faulty and replacing parts will not fix the problem."
• "If the test plan provides the message “The event memory could not be read." Then the starter/generator is not faulty and replacing the parts will not fix the problem."

These warnings emphasize the importance of accurate diagnosis to avoid unnecessary part replacements.

Technical Background

The 48V electrical system, along with the Belt Starter Generator (BSG), is a sophisticated component designed to provide electrical power efficiently. Unlike traditional alternators that continuously output full voltage, the BSG's power output is regulated based on the vehicle's current needs. A hardware-related issue within this system can cause the BSG to stop functioning as intended, leading to the observed malfunction and warning messages.

Diagnosis and Repair Procedure Summary

To address the Audi 48V electrical system malfunction, technicians must follow a specific diagnostic and repair procedure using a VAS tester with the current version of ODIS software. The process involves several key steps:

1. Preparation: Ensure both the 48V and 12V batteries are properly charged before beginning diagnostics. Reference TSB 2067906 for detailed battery charging instructions, especially concerning DTC P0A7D00.
2. Function Test: Perform the