2025-2026 Audi Driver Assist System Fault C12BFF2

Audi has issued Technical Service Bulletin (TSB) 2077141/5 to address issues with multiple driver assist systems becoming unavailable in certain 2025-2026 Audi A5, S5, Q5, and SQ5 models. Owners may notice various warning messages in their instrument cluster, indicating a malfunction in these advanced safety features. This TSB provides a solution primarily involving a software update to restore full functionality.

This specific Audi driver assist fault C12BFF2 is linked to a software error detected in the vehicle's short-range radar sensors. Resolving this issue is crucial for maintaining the intended safety and convenience features of your Audi.

Why This Matters

Modern Audi vehicles are equipped with sophisticated driver assistance systems designed to enhance safety and driving comfort. When these systems become unavailable, features like blind-spot monitoring, rear cross-traffic alerts, and emergency braking assistance may not function as expected. This can potentially reduce a driver's awareness of their surroundings and the vehicle's ability to react to hazards, impacting overall road safety.

Symptoms You Might Notice

Owners of affected Audi vehicles may observe one or more of the following messages appearing in the instrument cluster, indicating an Audi driver assist fault C12BFF2:

• "Rear turn assist: fault. You can continue driving. See owner's manual."
• "Lane change assist: fault. You can continue driving. See owner's manual."
• "Exit warning system: fault. You can continue driving. See owner's manual."
• "Rear cross-traffic assist: fault. You can continue driving. See owner's manual."
• "Proactive occupant protection: currently restricted. See owner's manual."
• "Active front assist: currently unavailable. See owner's manual."

These messages indicate that the respective driver assist functions are not operational. While the vehicle remains drivable, the absence of these safety features can be a significant concern for owners.

Fault Codes / DTCs

When diagnosing this issue, technicians will typically find the Diagnostic Trouble Code (DTC) C12BFF2 stored in the vehicle's control units. Specifically, this DTC is identified as "C12BFF2: Radar sensor software error detected (symptom number 1289)". This error is found in the Short-Range Radar 3 & 4 (-J769-/-J770-) and Short-Range Radar 1 & 2 (-J1088-/-J1089-) control units, which are responsible for object detection.

Important Warning Regarding DTC C12BFF2 (1282)

It is critical to note that the TSB includes a specific warning: "The event memory entry 'C12BFF2: Radar sensor software error detected' (symptom number 1282) does not lead to a customer complaint and can be ignored. NO measures are necessary." This means if your vehicle only shows DTC C12BFF2 with symptom number 1282, and no actual driver assist system faults are present, no repair is required. This distinction helps prevent unnecessary diagnostic work and part replacements.

Diagnosis and Trigger Conditions

The Audi driver assist fault C12BFF2 is a functional issue stemming from software and hardware interaction within the driver assistance systems. It specifically points to a software error in the short-range radar sensors. These sensors are vital for the proper operation of many driver assist features, including those related to rear turn assist, lane change assist, and active front assist.

Repair Procedure Summary

The primary solution outlined in Audi TSB 2077141/5 involves performing a software update. This update is detailed in a separate document, TSB 2079690, titled "00 Combined software update 03.10.00/C (28.13.01) KD2". This combined software update is designed to correct the underlying software issues causing the radar sensor errors and subsequent driver assist system malfunctions.

During the software update process, a battery charger must be connected to the vehicle to ensure stable voltage. The procedure includes all necessary preliminary and follow-up work, such as bus sleep cycle management and calibration drives, which are essential for the proper functioning of the updated systems. In some cases, if the software update does not resolve the issue, or if a flash abort occurs, the TSB mentions potential replacement of components like the object detection control unit or the lane change assist control unit. However, the initial and most common remedy is the software update.

Required Tools or Parts

For the software update, a stable power supply is critical. Therefore, a suitable battery charger is a required tool during the service procedure. While the TSB primarily focuses on software, it also lists labor operations for potential parts replacement, including:

• Object detection control unit
• Lane change assist control unit

These parts would only be considered if the software update fails to resolve the Audi driver assist fault C12BFF2.

Owner Action

If you are experiencing any of the described driver assist system fault messages in your 2025-2026 Audi A5, S5, Q5, or SQ5, it is recommended to schedule an appointment with an authorized Audi dealership. Inform them about the specific symptoms you are observing and mention Technical Service Bulletin 2077141/5. The dealership technicians will diagnose the issue, confirm the presence of DTC C12BFF2 (1289), and perform the necessary software update. This service is typically covered under warranty if your vehicle is still within the applicable warranty period.

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Source: NHTSA ID: 11027401