Audi Start-Stop Failure Causes Random Engine Shutdowns

I had a very similar issue with my Audi A6 2010 last winter. With moderate experience working on cars, I initially thought it was just the eco mode acting up, but it turned out to be more serious. The symptoms matched yours exactly, unusual engine stalling, warning lights, and the starter motor struggling to turn over. After the car battery completely died one morning, I took it to a workshop for diagnosis. The technician found that the car battery was heavily discharged and no longer holding proper charge. These start-stop systems are particularly demanding on batteries, and they need special AGM (Absorbent Glass Mat) batteries designed for frequent cycling. The repair cost me 290 Euro for a new AGM battery plus installation. Since then, the automatic restart feature works flawlessly again, and no more unusual engine stalling. Before suggesting more specific solutions, could you share: Has the battery ever been replaced? Are there any other electrical issues? What error codes are stored? Does the problem occur more frequently when the engine is cold or warm?

Had my last service at 118864 KM and the mechanic found multiple error codes related to voltage drops. The battery issue was much worse than initially thought. The starter motor drew excessive current and damaged the original AGM battery over time. In addition to battery replacement, the starter motor needed rebuilding due to worn brushes causing the sluggish start problems. After replacing both parts, the car starts reliably and the engine stalling has completely stopped. The automatic restart now works perfectly. Total repair came to 890 Euro, 290 Euro for the AGM battery and 600 Euro for the starter motor work. While expensive, it resolved all symptoms completely. For anyone facing similar issues, the key warning signs were the sluggish starting and voltage-related error codes, even before the car battery showed obvious signs of failure.

Good to hear you got this resolved. Your repair experience matches what I discovered with my Audi A6, these start-stop systems really expose any weakness in the charging system. The starter motor damage you mentioned explains why my repair costs were lower. My battery was the only failing component, while your worn starter brushes created a cascade effect, draining the battery faster due to the higher current draw. Since the fix, my start-stop system has worked perfectly for over 18 months now. The idle stop feature activates smoothly, and the engine restarts instantly every time. No more warning lights or error codes related to voltage drops. One thing worth mentioning, the AGM battery installed needs regular testing since the start-stop system puts significant strain on it. A battery health check during annual service can prevent similar issues from developing again. The total repair cost of 890 Euro seems reasonable considering both the battery and starter motor needed work. These components are critical for the start-stop system reliability, and fixing them properly prevents more expensive issues down the road.

As the original poster, I want to provide an update on my complete experience with the repair for future reference: The voltage drop error codes discovered during my service at 118864 KM turned out to be critical warning signs. My battery issue was more severe than expected, with the faulty starter motor drawing excessive current and gradually damaging the AGM battery. The automatic restart problems and engine stalling were direct results of these failing components. The repair involved two main parts: First, replacing the original AGM battery that could no longer handle the demands of the start-stop system. Second, rebuilding the starter motor which had worn brushes causing the sluggish starts. Total cost breakdown came to 890 Euro: AGM battery replacement: 290 Euro, Starter motor rebuild and labor: 600 Euro The investment was worth it, all symptoms have completely resolved. No more engine stalling, the start-stop system works perfectly, and the idle stop feature operates as designed. For others facing similar issues, watch for sluggish starting and voltage-related error codes before complete battery failure occurs. Regular battery testing during maintenance is now part of my service routine to prevent future issues with the start-stop system.