2021-2023 Audi MHEV Electrical System Fault TSB 2073284/4

Audi has issued Technical Service Bulletin (TSB) 2073284/4 to address instances of an "MHEV Electrical System Fault" in various 2021-2023 models. This bulletin provides critical guidance for diagnosing and resolving the issue, which can manifest with several diagnostic trouble codes (DTCs) and dashboard warnings. The TSB clarifies that simply replacing the 48V Starter/Generator is not the correct solution for this particular problem.

Symptoms

Owners of affected Audi vehicles may observe several indicators of an Audi MHEV Electrical System Fault. These include:

• An "electrical system fault" message appearing in the instrument cluster.
• A "yellow/red battery warning symbol" lighting up in the instrument cluster.
• The "battery charge level information display" activating.
• In some cases, the engine may experience a misfire during operation.

Workshop findings often confirm these symptoms, noting that the address word 00CC (belt-driven starter-alternator) may be unreachable, and numerous DTCs are stored in the Engine Electronics (address word 0001) or Brake Electronics (address word 0003).

Fault Codes / DTCs

The Audi MHEV Electrical System Fault is commonly accompanied by one or more of the following diagnostic trouble codes (DTCs):

Diagnostic Address	Diagnostic Trouble Code	Fault Symptom	Storage State
0001 - Engine	U012000	Lost Communication With Starter / Generator Control Module	Intermittent
0001 - Engine	U012000	Lost Communication With Starter / Generator Control Module	static
0001 - Engine	U046900	Invalid Data Received From Starter / Generator Control Module	Intermittent
0001 - Engine	U046900	Invalid Data Received From Starter / Generator Control Module	static
0001 - Engine	U002800	Vehicle Communication Bus A	Intermittent
0001 - Engine	U002800	Vehicle Communication Bus A	static
0001 - Engine	U002900	Vehicle Communication Bus A Performance	Intermittent
0001 - Engine	U002900	Vehicle Communication Bus A Performance	static
0003 - Brake	C054A00	Vacuum Sensor "A" Range/Performance	Intermittent
0003 - Brake	C054A00	Vacuum Sensor "A" Range/Performance	static
0003 - Brake	C11EC04	Brake booster pressure sensor faulty	Intermittent
0003 - Brake	C11EC04	Brake booster pressure sensor faulty	static

Specifically, DTC U046900 is often seen with symptom code 34763, indicating lost communication with the Starter/Generator Control Module. DTCs U002900 and U002800 point to issues with Vehicle Communication Bus A.

Diagnosis and Trigger Conditions

The TSB 2073284/4 highlights that the presence of DTC U046900, indicating lost communication with the Starter/Generator Control Module, does not necessarily mean the 48V Starter/Generator itself is faulty. Instead, this DTC is often a secondary symptom of another electrical system problem within the vehicle. The expanded ambient conditions of the event memory may show a value of "Starter generator, actual mode 48V = 8".

Potential causes for the communication fault DTCs (U002900 and U002800) include improperly plugged-in or fastened communication connectors, bent or widened pins, short circuits in the wires, or incorrect attempts to swap connectors (such as failing to connect vehicle ground cables). Additionally, any residual fluids, like coolant, in the connectors of the belt-driven starter-alternator (especially after prior repairs) can interfere with communication.

Important Warnings

• Do not replace the 48V Starter/Generator: The TSB explicitly states that replacing the 48V Starter/Generator will not resolve the Audi MHEV Electrical System Fault. The DTC U046900 is a symptom of other issues.
• ODIS diagnostic access: If the Starter Generator (diagnostic address 00CC) cannot be reached in ODIS, this does not automatically mean the component is faulty.

Repair Procedure Summary

The correct approach to resolve the Audi MHEV Electrical System Fault involves a thorough diagnostic process rather than immediate component replacement. Technicians should prioritize the following steps:

1. Address Pressure Sensor DTCs: First, process any pressure sensor DTCs found in the brake electronics. These can impact the vehicle's data bus system.
2. Process Communication Fault Entries: Next, address communication fault entries. Faults on these sensors can cause the engine control unit to send the belt-driven starter-alternator into freewheel, leading to electrical system faults.
3. Inspect Connectors: Carefully inspect communication connectors for the 48V Starter/Generator. Ensure they are correctly plugged in and fastened. Check for bent or widened pins, as well as any short circuits in the wiring.
4. Check for Fluids: Examine the connectors on the belt-driven starter-alternator for any remaining fluids, such as coolant, which could be causing communication issues.

This methodical approach, as outlined in TSB 2073284/4, is crucial for accurately identifying and rectifying the root cause of the problem.

Required Software Versions

For the 00CC - Starter generator control unit, the following software versions are referenced in relation to this issue:

• 0523
• 0527
• 0560
• 0562

Owner Action

If your 2021-2023 Audi vehicle is displaying an "electrical system fault" warning, a battery warning symbol, or exhibiting any of the associated symptoms or DTCs, it is recommended to schedule an appointment with an authorized Audi service center. Provide them with details of the symptoms you are experiencing. Referencing TSB 2073284/4 can help ensure your technician follows the correct diagnostic and repair procedures.

NHTSA ID: 11016528