2025 Audi Q5/SQ5 Headlight Defect TSB 2078609/4

Owners of certain 2025 Audi Q5 and SQ5 models may encounter an intermittent warning message in their instrument cluster stating, "Left/right main beam headlight defective. See owner's manual." This issue, identified by Technical Service Bulletin (TSB) 2078609/4, is a known software-related problem that does not affect the actual functionality of the main beam headlights.

This TSB, released on December 11, 2025, provides a solution for the Audi Q5 headlight defective warning. The warning typically appears while driving and, although it disappears after cycling the ignition off and on, it will reappear intermittently. Despite the warning, there are no functional restrictions or performance issues with the main beam headlights.

Symptoms of the Headlight Warning

The primary symptom is the yellow warning message, "Left/right main beam headlight defective. See owner's manual," displayed in the vehicle's instrument cluster. This message indicates a perceived fault within the headlight system. The warning is intermittent, meaning it may not be present every time the vehicle is driven, but it will reoccur.

Crucially, despite the warning, the main beam headlights continue to function normally. There are no functional restrictions, and the headlights illuminate as expected. This indicates the issue is a reporting error rather than a physical defect affecting the light output.

Diagnostic Trouble Code (DTC) C12FC01

When a technician diagnoses the vehicle, the specific diagnostic trouble code (DTC) found will be C12FC01. This code is further detailed as "C12FC01 LED channel 4, electrical fault, symptom 139272." The fault code is typically stored in diagnostic address 0029, which corresponds to the Left light control module, and/or diagnostic address 0039, which is for the Right light control module.

This DTC confirms the presence of the software issue causing the Audi Q5 headlight defective message. The symptom code 139272 helps technicians pinpoint the exact nature of the electrical fault being reported by the system, even though no actual electrical malfunction is present.

Technical Background

The root cause of the "Left/right main beam headlight defective" warning and DTC C12FC01 is a software issue within the vehicle's control modules. This means the vehicle's computer system is misinterpreting certain data or conditions, leading it to incorrectly report a fault with the main beam headlights.

Audi has identified this as a software-only problem, which is why there are no functional limitations to the headlights despite the warning message. The issue is not related to faulty hardware or wiring, but rather how the software processes and communicates information regarding the headlight status.

Repair Procedure Summary

The resolution for the Audi Q5 headlight defective warning involves a software update. Technicians are instructed to perform TSB 2079690 00, which is a combined software update with version 03.10.00/C (28.13.01) KD2. This update specifically addresses the software anomaly that triggers the warning message and DTC C12FC01.

The repair process includes connecting a battery charger to maintain stable voltage during the software update. The labor operation for this procedure is typically identified by service number 9407 and damage code KD02. The fixed rate for the software update includes all necessary preliminary and follow-up work, such as bus sleep cycle management and calibration drives, ensuring a comprehensive resolution to the issue.

Important Owner Information Regarding Warranty

Owners should be aware of the warranty implications for this Technical Service Bulletin 2078609/4. If the vehicle is still under its original warranty, the software update will be performed at no charge. However, if the vehicle is outside of its warranty period, this Technical Service Bulletin is considered informational only, and any associated costs for the software update may be the owner's responsibility.

It is recommended to contact an authorized Audi dealership to confirm your vehicle's warranty status and schedule the necessary software update. The update is crucial for resolving the intermittent warning message, even though the headlight function itself is not impaired.

Superseded Bulletins

This Technical Service Bulletin 2078609/4 replaces a previous bulletin, PSS 2078182, which also addressed the "94 Warning lamp in instrument cluster: 'Left/right main beam headlight defective. See owner's manual' DTC C12FC01." Owners or technicians searching for information on the older PSS 2078182 should refer to this updated TSB for the most current information and repair procedures.

Source: NHTSA ID 11027362