Audi S5 Diesel: Fuel System Drift Issues & Solutions

Having dealt with similar fuel injection problems on my 2020 Audi S4 diesel, I can share my experience, as I have some hands-on experience with these modern diesel engines. The symptoms you describe match what I encountered, rough running and check engine warnings related to fuel quantity. The car sensors initially pointed to drift compensation issues, but the root cause turned out to be a faulty injector. The workshop performed comprehensive diagnostics using specialized equipment to check the fuel injection system. They found one injector was not providing consistent spray patterns, affecting overall engine performance. The repair involved: Complete fuel injector testing, Replacement of the defective injector, System recalibration, Performance tuning adjustments, Reset of all relevant sensor data Total cost was 515 Euro including parts and labor. After the fix, fuel economy improved noticeably and the engine ran smoothly again. To provide more specific advice, could you share: Current mileage on your S5? When did the symptoms first appear? Any unusual sounds during cold starts? Have you noticed increased fuel consumption? Are there any other warning lights besides check engine? This information would help determine if your issue matches what I experienced.

Thanks for the detailed input. My S5 shows 10271 KM and has been properly serviced according to schedule. I will check the injector symptoms you mentioned. After connecting my onboard diagnostics tool, I noticed the fuel quantity adaptation values are indeed off. The cold starts have been normal so far, but fuel economy dropped about 15% in the past weeks. No other warning lights present besides the check engine light. Will have the dealer verify the injector spray patterns before proceeding with recalibration.

Thanks for providing those additional details about your S5. Based on the diagnostic data you shared, your symptoms strongly align with what I experienced on my S4. At similar mileage, I also saw fuel quantity adaptation values outside normal range before discovering the injector issue. The 15% fuel economy drop matches the pattern I observed before my repair. With modern diesel engines, the onboard diagnostics are quite precise in identifying these drift compensation issues. However, while sensor data can point to injector problems, proper spray pattern testing is essential for accurate diagnosis. One tip from my experience: have them check all injectors while testing, not just the suspect one. In my case, a second injector showed early wear signs during testing, though it hadn't triggered any car sensors yet. Addressing both prevented a repeat issue months later. The fact your cold starts remain normal is actually positive, suggests the issue likely hasnt progressed as far as mine did. In terms of performance tuning after repair, my S4 required minimal adjustment to restore optimal operation. Keep us posted on what the dealer finds with the injector diagnosis. The repair should resolve both the rough running and restore your normal fuel economy.

Thanks for the input. Just got the car back from the dealer and wanted to share the outcome. The onboard diagnostics were spot-on, they found two injectors with irregular spray patterns during testing. Both were replaced and the fuel injection system was fully recalibrated. Total repair cost came to 890 Euro with parts and labor. After the system reset and performance tuning, the engine runs perfectly smooth again. Fuel economy is back to normal and the check engine light cleared completely. The airflow sensors were also checked and recalibrated as part of the service. Really glad I had this checked before the issue got worse. The comprehensive testing definitely saved time in diagnosing the exact problem. For anyone else seeing similar symptoms, the drift compensation values from diagnostics were a reliable indicator of the underlying injector issues. Will update in a few weeks about long-term performance, but so far very satisfied with the repair outcome. The car feels as responsive as new.