2025-2026 Audi A5/S5/Q5/SQ5 P064F00 MIL On TSB

Symptoms of the P064F00 MIL On Issue

Owners of 2025-2026 Audi A5, S5, Q5, and SQ5 vehicles may encounter specific symptoms related to this issue. The primary indication is the illumination of the Malfunction Indicator Lamp (MIL), commonly known as the "Check Engine Light," or the "Exhaust emission warning lamp." This warning light signals a problem within the vehicle's emission control system or engine management.

A more severe symptom reported by owners is that the engine may not start. It's important to note that, according to Audi TSB 2078914/4, these symptoms are typically observed when diagnostic work is being performed in a workshop setting, suggesting the issue might be triggered by specific diagnostic procedures rather than occurring spontaneously during normal driving.

Understanding DTC P064F00

When the MIL illuminates, a diagnostic scan will reveal specific fault codes stored in the Engine Control Module (ECM), identified as J623 (address word 0001). The key Diagnostic Trouble Code (DTC) associated with this problem is P064F00.

This code is specifically described as "Unauthorized software/coding detected P064F00 active." This means the ECM has identified a discrepancy or corruption in its software or calibration data, leading it to believe that unauthorized changes have been made. The fault status is typically reported as "active/static," indicating a persistent issue. Additional internal diagnostic identifiers include Symptom 10529 and Status 10100111, which provide further detail for technicians.

Technical Background of the ECM Coding Loss

Audi's technical analysis indicates that the coding for the engine control unit (ECM, J623) may be lost during the ODIS diagnosis process conducted in the workshop. ODIS (Offboard Diagnostic Information System) is Audi's proprietary diagnostic software used by dealerships and authorized service centers. The loss of ECM coding is a critical event, as the ECM relies on precise programming to manage engine functions, emissions, and overall vehicle performance.

At the time of the bulletin's release, the precise cause of this coding loss during ODIS diagnosis was still under analysis by Audi. This suggests that while the symptom and the solution are identified, the underlying trigger within the diagnostic process was still being investigated to prevent future occurrences.

The Recommended Repair: Software Update

To resolve the "MIL on" and DTC P064F00 issue in affected 2025-2026 Audi A5, S5, Q5, and SQ5 vehicles, Audi recommends a specific software update. The repair procedure is detailed in a separate, related bulletin: TSB 2079690, titled "00 Combined software update 03.10.00/C (28.13.01) KD2."

This repair involves performing a comprehensive software update on the vehicle's engine control unit. During this process, it is crucial to connect a battery charger to maintain stable voltage, as software updates can be sensitive to power fluctuations. This ensures the update is completed successfully without further data corruption or module damage. The software update is a dealer-performed service, requiring specialized diagnostic equipment and trained technicians.

Warranty Coverage and Service Information

For vehicles experiencing the "Audi A5 P064F00 MIL" issue, warranty coverage is a key consideration. Audi Technical Service Bulletin 2078914/4 specifies that if the vehicle is outside of its warranty period, this Technical Service Bulletin is for informational purposes only, meaning the repair costs would likely fall to the owner. All warranty claims must adhere to the Audi Warranty Policies and Procedures Manual and are subject to review or audit by Audi Warranty.

Dealers will use Service Number 2470 and Damage Code KD02 for warranty claims related to this issue. The labor operations for this repair include:

• 0151 0010: Software update, including connecting a battery charger.
• 0151 0040: Fixed rate for the software update, covering all required preliminary and follow-up work, including bus sleep cycle, calibration drives, and additional tasks.
• 0150 9999: An additional lump sum of 50 time units can be claimed per each documented attempt if additional attempts are required after a flash abort.

Important Considerations for Owners

Owners of affected 2025-2026 Audi A5, S5, Q5, and SQ5 models should be aware of several important points. If your vehicle displays the "MIL on" light or experiences engine start issues, especially after a diagnostic visit, it is advisable to contact an authorized Audi service center. Mentioning the specific DTC P064F00 and TSB 2078914/4 can help technicians quickly identify the problem and apply the correct solution.

Audi emphasizes that all part and service references provided in TSB 2078914/4 are subject to change and/or removal. Technicians are instructed to always check with their Parts Department and/or ETKA (Audi's electronic parts catalog) for the latest information and bulletins. Furthermore, the Repair Manual should always be consulted for any fasteners, bolts, nuts, and screws that require replacement during the repair process. For warranty billing, time stamps are not required for the combined software update, allowing technicians to work on multiple vehicles simultaneously or for non-productive personnel to perform the update.

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Source: NHTSA ID: 11027409, Manufacturer Communication Number: 2078914/4