Audi S5 Engine Stalls: Idle Stop Warning Signs

I experienced a similar issue with my Audi S4 2011, and having some experience working on cars, I initially thought it was just a minor sensor problem. The symptoms matched exactly what you described, engine stalling, warning lights, and the idle stop feature stopped working. Like you, my car would start normally most times, which made me think the car battery was fine. However, the automatic restart became increasingly unreliable. After attempting basic troubleshooting, I took it to my regular workshop. They diagnosed a heavily discharged battery that was causing the hybrid vehicle systems to malfunction. Even though the car would start, the battery wasnt maintaining proper voltage under load. The repair cost was 290 Euro including a new battery and system check. The engine stalling issues completely disappeared after the battery replacement. These symptoms are often misdiagnosed as sensor or fuel system problems, but the battery is a common culprit in these models. Could you share: Current mileage, When was the last battery replacement, Any modifications to the electrical system, Are you using the original battery size and specs This information would help determine if your issue is similar to what I encountered.

Thanks for sharing your experience. Based on your feedback, I suspect our issues might be related. My latest service was done at 108891 KM and the battery is actually original. After reading your post, I checked the battery voltage and noticed it fluctuates more than it should. The engine stalling happens more frequently during cold starts, and the starter motor seems to work harder than usual. The automatic restart feature completely stopped working last week, which matches what you described about your battery issues. Your repair path sounds promising since our symptoms align. Will have the battery and charging system checked first before exploring other potential causes. Thanks everyone for the feedback so far.

Thanks for the update. The original battery at that mileage definitely points to the source of your problems. In my case, the starter motor also showed similar symptoms of working harder before the battery replacement. The cold start issues you mentioned are classic signs of a weak battery, especially with these start-stop systems. The automatic restart feature requires significant power, and when the battery gets weak, it is one of the first functions to fail. After my battery replacement, I learned these Audi models are particularly sensitive to battery health. The idle stop and engine stalling issues disappeared completely once the new battery was properly coded to the vehicle. The warning lights also cleared up after the system reset. One tip from my experience: make sure to get an AGM battery with the correct specifications. A standard battery, even with similar specs, can cause issues with the hybrid vehicle systems and automatic restart features. Based on your voltage readings and symptoms matching my previous situation, I would prioritize the battery replacement before investigating other potential issues.

Thanks for the detailed feedback everyone. I checked the battery specifications, and found that I indeed have the original AGM battery from 2009. The voltage readings I took show 11.8V when idle and drop to 11.2V under load, which seems quite low. The start-stop system problems and engine stalling make much more sense now. Its clear that the battery issue is affecting multiple systems, especially since the automatic restart stopped working completely. I will schedule a battery replacement this week and make sure they code it properly to the vehicle. Since the original battery lasted 14 years, I will stick with a high-quality AGM replacement that matches factory specifications. Will update once the work is done, but based on the matching symptoms and diagnostic findings shared here, I am confident this will resolve the engine stalling and warning light issues. Thanks for helping me avoid potentially expensive diagnostic work chasing other problems.