2021-2023 Audi 48V Electrical System Warning U046900 TSB

Owners of certain 2021-2023 Audi A6, A7, Q7, and Q8 models equipped with the 48V mild hybrid system may encounter an "Electrical system: malfunction! Please contact Service" warning message on their instrument cluster. This issue is often accompanied by a yellow warning lamp related to the electrical system and the storage of Diagnostic Trouble Code (DTC) U046900 in the Engine Control Module (ECM).

Audi Technical Service Bulletin (TSB) 2058831/16 provides diagnostic and repair procedures for this specific concern, which can stem from either hardware or functional software issues with the belt-driven starter-alternator.

Symptoms

If your Audi is affected by this issue, you may observe the following symptoms:

• The message "Electrical system: malfunction! Please contact Service" is displayed on the instrument cluster.
• A yellow warning lamp related to the electrical system illuminates in the instrument cluster while driving.

These symptoms point to a problem within the 48V electrical system, specifically concerning the starter/generator control module, leading to the Audi 48V electrical system warning U046900.

Fault Codes / DTCs

Technicians diagnosing this issue will typically find the following Diagnostic Trouble Code (DTC) stored in the Engine Control Module (ECM), J623 (address word 0001):

Diagnostic Trouble Code	Diagnostic Address	Fault Symptom	Storage State
U046900	0001 - Engine electronics	Invalid Data Received From Starter / Generator Control Module	Intermittent
U046900	0001 - Engine electronics	Invalid Data Received From Starter / Generator Control Module	static
U046900	0019 - Data Bus OBD Interface	Invalid Data Received From Starter / Generator Control Module	Intermittent
U046900	0019 - Data Bus OBD Interface	Invalid Data Received From Starter / Generator Control Module	static

Additionally, if the starter-alternator requires replacement, DTC B200096, indicating a "Faulty control module (active/static or passive/intermittent)", may be present in the ODIS test plan.

Important Warnings

Audi has issued crucial advisories for technicians and owners regarding this issue:

• Symptom 36564: This TSB (2058831/16) only applies if symptom 36564 ("Invalid data received from starter/generator control module") is present. If this specific symptom is not identified, this bulletin does not apply.
• Battery Charge: While diagnosing the 48V system, it is essential to ensure both the 48V and 12V batteries are properly charged prior to following the procedure. Failure to do so may prevent accurate diagnosis. Refer to TSB 2067906: "27 48V Reference: Charging 48V Battery with 12V Charger DTC P0A7D00 / P0B2900" for proper charging procedures.
• Starter-Alternator Replacement Risks: If the belt-driven starter-alternator needs replacement, there is a risk of damage to the radiator outlet coolant temperature sender G83 or communication problems with the new starter-alternator due to coolant entering the electrical connector. Technicians must seal electrical connectors on the coolant temperature sender, mating connector, and the signal connector to the belt-driven starter-alternator using a leak-tight connector -T40348- or suitable workshop materials. Visual inspection for moisture and cleaning electrical contacts are required before assembly.

Diagnosis

To diagnose the Audi 48V electrical system warning U046900, technicians should first check if the ODIS S software is updated to the latest version. After ensuring proper battery charge, a specific function test, "C29 – read_delete and attach to test plan", should be selected within the ODIS diagnostic system. When prompted, the answer "YES" should be provided to the question, "Are you running this program based on an instruction in a TPI?".

The ODIS paths to access these functions vary by model:

• For Audi A4/A5/Q7: Navigate through Body > Electrical system > 01 - On Board Diagnostic capable systems > CC - starter-alternator -C29 > CC - Functions > 00CC - Check/erase event memory entry.
• For Audi A6/A7/A8/Q8: Navigate through Diagnostic capable system > 00CC - starter alternator -C29 > 00CC - Functions > 00CC - Check/erase event memory entry.

If the DTC U046900 or B200096 is present in the ODIS test plan, it indicates a potential issue with the starter/generator control module.

Repair Procedure Summary

The primary repair for the Audi 48V electrical system warning U046900 involves replacing the belt-driven starter-alternator if DTC B200096 is stored in the ODIS test plan. This replacement should be performed according to instructions found in ETKA and the relevant Repair Manual. Before reassembly, technicians must carefully seal all electrical connectors associated with the coolant temperature sender and the starter-alternator to prevent coolant intrusion, which can lead to further damage or communication issues. Visual inspection for moisture and thorough cleaning of electrical contacts are critical steps.

If DTC B200096 is not stored, the generator is not considered faulty, and replacing parts will not resolve the problem. The TSB also references a "working_aid_for_necessary_functional_tests.pdf" document, attached to the bulletin, which contains function checks in ODIS required for workshop visits when the belt-driven starter-alternator needs replacement.

Required Tools or Parts

While specific part numbers are not listed directly in this TSB (2058831/16), technicians are advised to consult ETKA and the Repair Manual for the latest information on required parts, fasteners, bolts, nuts, and screws. A leak-tight connector, part number -T40348-, or suitable workshop materials are necessary for sealing electrical connections during the repair process.

Warranty Information

Warranty claims for this repair must adhere to the Audi Warranty Policies and Procedures Manual. The service number for this repair is 2726, with a damage code of 0040.

• If the starter-alternator is NOT replaced: Labor operations GFF (0150 0010 or 0150 0060) apply.
• If the starter-alternator IS replaced: Labor operations for replacement (2726 19xx / 2726 55xx) and 12V battery charge (2706 8950) apply, along with GFF (0150 0060).

If the vehicle is outside of warranty, this Technical Service Bulletin is for informational purposes only, and repair costs would typically be borne by the owner.

What Owners Should Know

If your 2021-2023 Audi A6, A7, Q7, or Q8 displays an Audi 48V electrical system warning U046900 or the message "Electrical system: malfunction! Please contact Service", it is important to have your vehicle inspected by an authorized Audi service center. This issue relates to the 48V mild hybrid system, which is a critical component of your vehicle's electrical system. Prompt diagnosis using the procedures outlined in TSB 2058831/16 can help identify whether a starter/generator control module replacement is necessary. Be aware that proper battery charging and careful sealing of electrical connections are vital steps in this repair to prevent future issues.

Source: NHTSA ID: 11016512