2021-2025 Audi U010100 Lost Communication with TCM TSB

Symptoms of Audi U010100 Lost Communication

Owners of 2021-2025 Audi A3, S3, RS 3, and Q3 vehicles might notice a warning or indicator lamp illuminated in the instrument cluster. This symptom is often associated with the Diagnostic Trouble Code (DTC) U010100, which signifies "Lost Communication with TCM" (Transmission Control Module).

However, it's important to note that this DTC can also be identified by technicians during routine maintenance or inspection without any active customer complaint or visible warning lights. In such cases, the fault is often intermittent and may trigger messages like "ABS malfunction display" or "brake failure warning display".

Diagnostic Trouble Code (DTC) U010100

The primary diagnostic trouble code addressed by Audi Technical Service Bulletin 2074475/3 is:

Diagnostic Address	Diagnostic Trouble Code	Fault Symptom	Storage State
0023 - Brake boost	U010100: Lost Communication with TCM	Intermittent

This DTC U010100 is specifically linked to the electromechanical brake servo (diagnostic address 23) and may appear with symptom codes 107008, 108560, or 108624. These symptom codes are associated with software version 553.

Technical Background of the Issue

Audi has identified that the presence of the U010100 Lost Communication with TCM fault code is often due to a software issue within the electromechanical brake servo control unit. This software anomaly can trigger the DTC without necessarily indicating a functional problem with the vehicle's braking system or transmission communication.

Important Information for Owners and Technicians

Audi Technical Service Bulletin 2074475/3 provides crucial guidance regarding the U010100 Lost Communication with TCM fault:

• DTC U010100 in A3 8Y and Q3 F3 models with specific software versions (0372, 0272, 0307, 0309, 0553 for A3 8Y; 0372, 0272, 0207, 0209 for Q3 F3) in the electromechanical brake servo does NOT lead to a customer complaint and CAN BE IGNORED. Technicians are instructed to log permission to ignore this DTC in ODIS.
• If a warning or indicator lamp IS lit in the instrument cluster, there must be a different underlying cause. In such cases, the U010100 DTC alone is not the reason for the warning light, and further diagnosis is required to identify the actual problem.
• This TSB is informational only and is NOT applicable to any Audi Warranty claims. This means that diagnosis and resolution of actual issues (if a warning light is present) would follow standard warranty procedures, but the mere presence of the ignorable U010100 code without symptoms does not constitute a warranty repair.

What Owners Should Do

If you own a 2021-2025 Audi A3, S3, RS 3, or Q3 and encounter a warning or indicator lamp illuminated on your dashboard, it is recommended to have your vehicle inspected by an authorized Audi service center. While the U010100 Lost Communication with TCM fault itself might be ignorable under specific conditions, an active warning light indicates a separate issue that requires attention.

If your vehicle is undergoing routine maintenance and a technician informs you about the U010100 DTC without any active warning lights or noticeable driving issues, refer to this Technical Service Bulletin 2074475/3. The TSB clarifies that under these circumstances, the code can often be disregarded as a software anomaly.

Revision History of TSB 2074475/3

This Technical Service Bulletin has undergone several revisions:

• Revision 3 (February 24, 2025): Revised Condition with updated information.
• Revision 2 (July 26, 2024): Revised header (Add Model Year), Revised Condition with updated information, and Revised Service with updated information.
• Revision 1 (July 03, 2024): Initial publication of the bulletin.

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Source: NHTSA ID: 11015767