2021-2026 Audi A3/Q3/S3/RS3 DTC U010100 Lost Communication

Audi has released Technical Service Bulletin (TSB) 2074475/4 to address instances of Diagnostic Trouble Code (DTC) U010100, which signifies "Lost Communication with TCM". This TSB applies to various 2021-2026 Audi models, including the A3, Q3, S3, and RS3.

This bulletin provides crucial guidance for technicians and owners regarding the interpretation and handling of the Audi U010100 Lost Communication fault, particularly when it appears without accompanying symptoms.

Important Warning for Owners

Audi explicitly states that if the DTC U010100 is identified in the electromechanical brake servo (diagnostic address 23) without a customer complaint or an active warning/indicator lamp in the instrument cluster, it can be ignored. This is a critical piece of information to prevent unnecessary repairs or parts replacement. Permission to ignore this specific condition must be logged in ODIS by service technicians.

Symptoms

Owners might notice one primary symptom related to this issue: "A warning/indicator lamp is lit up in the instrument cluster." However, the TSB clarifies that the presence of DTC U010100 alone, without an active warning light, does not constitute a customer complaint and can often be disregarded.

Fault Codes / DTCs

The primary Diagnostic Trouble Code addressed by this bulletin is U010100. This code indicates "Lost Communication with TCM" (Transmission Control Module).

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

This DTC may be accompanied by symptom codes 107008, 108560, and/or 108624, particularly when the electromechanical brake servo has specific software versions (e.g., 553).

Technical Background

The root cause of the Audi U010100 Lost Communication DTC is identified as a software issue within the electromechanical brake servo control unit. This software anomaly can cause the DTC to be stored intermittently without affecting the vehicle's functionality or triggering any noticeable problems for the driver.

Diagnosis and Conditions

Technicians may find the DTC U010100 stored in diagnostic address 23 (electromechanical brake servo) during routine maintenance or inspection. Specifically, for the Audi A3 (8Y platform) with software versions 0372, 0272, 0307, 0309, 0553, 562, or 563, and for the Audi Q3 (F3 platform) with software versions 0372, 0272, 0207, or 0209, the presence of DTC U010100 does not necessarily indicate a customer-perceptible problem.

What Owners Should Know

If your 2021-2026 Audi A3, Q3, S3, or RS3 has the DTC U010100 stored, but you are not experiencing any warning lights on your instrument cluster or other functional issues, this TSB advises that the code can be ignored. This specific condition is considered a software issue that does not lead to a customer complaint. However, if a warning or indicator lamp is lit up in the instrument cluster, it suggests a different underlying cause that requires further investigation by a qualified technician. The TSB 2074475/4 is informational and does not apply to any Audi Warranty claims.

Revision History

This Technical Service Bulletin has undergone several revisions to update its information:

• Revision 4: Updated the header to include additional model years and revised service information.
• Revision 3 (February 24, 2025): Revised condition details.
• Revision 2 (July 26, 2024): Updated the header for new model years, revised condition, and updated service information.

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Source: NHTSA ID: 11020376, Transaction No. 2074475/4