Audi S6 Starting Failure Points to ECU/Fuel System Fix

Had similar symptoms on my 2015 Audi S4 last month. Initially thought it was an ECU issue, but after proper diagnostics, it turned out the battery terminals had severe corrosion and loose connections. This caused inconsistent power delivery to the ECU and fuel injection system, triggering engine fault warnings and starting problems. The symptoms match exactly, intermittent starting issues, engine stalling, unusual warning lights, and false ECU readings. The car would sometimes start normally, then suddenly display multiple electrical faults. The fix required cleaning both battery terminals, replacing the corroded connectors, and ensuring proper contact. After the repair, the ECU performed a self-reset and all systems returned to normal operation. This is actually a common issue that can mimic serious ECU or fuel injection problems. While not a major repair, ignoring it can lead to more severe electrical system damage and potential engine surge issues. Before assuming ECU failure, have a qualified technician check the battery connections and electrical system. Poor connections can cause misleading diagnostic readings and unnecessary repairs.

Thanks for sharing your experience. After reading about your battery fix, I wanted to share that I faced engine stalling issues with my S6 with very similar symptoms. The engine fault warnings kept popping up out of nowhere. After getting the engine diagnostics done, it was indeed a failing ECU module that needed replacement. Would you mind sharing how much the battery terminal repair cost you? My ECU replacement was quite expensive and Im curious about the price difference. Also, have you experienced any other electrical issues since the repair?

Thanks for asking about the costs. The battery terminal fix at my mechanic came to 155 Euro total, which included cleaning and replacing the corroded connectors plus labor. This was way more reasonable than an ECU replacement would have been. Since fixing the loose cable connections, the engine control malfunction cleared completely. The engine software is running perfectly now with no electrical issues, warning lights, or engine surge problems. The car starts reliably every time without any ECU issues showing up on the dash. The mechanic actually showed me how deceptive these symptoms can be, what looks like major engine diagnostics problems often trace back to basic electrical connections. Its been 3 months now and everything is still working flawlessly.

I decided to take it to a different mechanic after seeing your replies. Turns out my engine fault warnings were definitely from a faulty ECU module. The new shop ran thorough engine diagnostics and confirmed the previous repairs were incomplete. The total bill came to 1250 Euro for the new ECU module, programming, and labor. While expensive, the engine software is now properly calibrated and the fuel injection system works perfectly. No more unusual engine stalling or warning lights. After 2 weeks of driving, I can say the car runs better than before. The new mechanic explained everything clearly and showed me the actual fault codes. Much better experience than my previous repair attempts. Looking back, getting a second opinion and proper engine diagnostics was worth it, even though the repair cost more than I hoped. At least the problem is fixed properly this time.