RS6 Random Stalling, Engine Start System Issues

I had a very similar issue with my 2016 RS7 last winter, sounds exactly like what you experienced. As someone with some hands-on experience maintaining performance vehicles, the symptoms immediately pointed to a car battery problem. The unusual stalling and start-stop system failures are classic signs of a weak or failing battery. My car was also showing multiple error codes because modern vehicles need stable voltage for all systems to work properly. Took it to a workshop where they diagnosed a heavily discharged battery that could no longer hold proper charge. The constant cycling from the start-stop system had worn it down faster than normal. They replaced the battery and recalibrated the start-stop system, total cost was 290 Euro. No issues since then. Before suggesting specific fixes, could you share: Current battery age? Do you use eco mode and start-stop features frequently? Any recent electrical upgrades installed? Does the starter motor sound normal when starting? What error codes are stored? This info would help determine if your case matches what I experienced or if there might be other underlying issues to investigate.

Thanks for sharing your experience. My battery is 2 years old but the automatic restart problems began recently. The start-stop system worked flawlessly until last month. The starter motor sounds normal during cold starts but occasionally makes a grinding noise during automatic restart attempts. Error codes point to voltage drops and starter motor circuit issues. No electrical upgrades installed. Last service was at 152000 KM with no battery-related concerns noted. The car battery voltage readings are unstable according to my OBD scanner, fluctuating between 11.8V-14.2V while driving. The workshop quoted 450 Euro for diagnosis and potential starter motor replacement. Wondering if I should first try a new battery before replacing the more expensive components.

Looking at your voltage readings and symptoms, this really does match what I experienced with my RS7. The fluctuating voltage and grinding noise during auto restarts are telltale signs of a failing battery, even if its only 2 years old. The start-stop system puts heavy strain on car batteries, much more than traditional starting. When the battery starts failing, it causes exactly these symptoms, engine stalling, warning lights, and starter motor strain from insufficient power during restart attempts. In my case, even though the original battery was relatively new, it had degraded faster due to frequent start-stop cycling. The grinding noise you mention during automatic restart is concerning, its likely the starter motor struggling with insufficient voltage, which could lead to damage if not addressed. Id strongly recommend replacing the battery first before considering starter motor replacement. My repair was straightforward: New AGM battery: 290 Euro, System recalibration included, Full reset of error codes The workshop wanting to jump straight to a 450 Euro starter motor replacement seems premature without first checking the simpler battery solution. A failing battery can mimic starter motor problems, especially in cars with start-stop systems. Monitor the voltage after battery replacement. If the grinding noise persists, then investigating the starter motor would make sense as a next step.

The feedback about checking the battery first makes a lot of sense. The idle stop issues and voltage readings definitely point toward the car battery being the likely culprit rather than a starter motor problem. I checked pricing at a few places and found AGM batteries ranging from 180-300 Euro. Much more reasonable than jumping straight to starter motor replacement. The unstable voltage readings from my OBD scanner really do suggest battery degradation is causing the automatic restart problems. Will get the battery replaced first and monitor if the start-stop system returns to normal function. Makes sense that constant cycling could wear down even a relatively new battery. If the grinding noise during restart continues after battery replacement, then I can always investigate the starter motor as a secondary issue. Really appreciate the detailed advice and cost comparison. Helped me avoid potentially unnecessary expensive repairs by addressing the most likely root cause first. Will update once I get the new battery installed and test if it resolves both the stalling and start-stop system problems.