2025 Audi Q5/SQ5 Headlight Defective Warning TSB 2078609/5

Owners of certain 2025 Audi Q5 and SQ5 models may encounter a dashboard warning message stating, "Left/right main beam headlight defective. See owner's manual." This issue, which can trigger the DTC C12FC01, indicates a software-related problem rather than a physical malfunction of the headlights. Audi has released Technical Service Bulletin (TSB) 2078609/5 to provide guidance for technicians on how to resolve this specific concern.

This TSB, released on February 19, 2026, and last revised on December 13, 2025 (Revision 4), clarifies that the warning is due to a software anomaly. It also supersedes a previous bulletin, PSS 2078182, which covered the same warning lamp issue in the instrument cluster. The primary solution involves a software update to the vehicle's control modules.

Symptoms

If your 2025 Audi Q5 headlight defective warning appears, you will typically observe the yellow warning message "Left/right main beam headlight defective. See owner's manual" displayed in the instrument cluster while driving. While this warning is active, there are no functional restrictions or performance limitations with the main beam headlights themselves. The warning lamp may disappear after switching the ignition off and then on again, but it often reappears intermittently during subsequent drives.

Fault Codes / DTCs

When diagnosing this issue, technicians will likely find Diagnostic Trouble Code (DTC) C12FC01 stored in the vehicle's diagnostic system. This specific code is identified as "LED channel 4, electrical fault" with symptom code 139272. The fault is typically found in diagnostic address 0029, which corresponds to the Left light control unit, and/or diagnostic address 0039, which corresponds to the Right light control unit. Despite the