Audi A3 Randomly Dies, Start-Stop System Failure Alert

Having worked on cars as a hobby for several years, I encountered a very similar battery issue with my 2002 Audi A4. The symptoms matched yours exactly, unusual engine stops and warning lights, particularly affecting the idle stop system. After multiple occurrences, I took it to a workshop where they diagnosed a heavily discharged car battery that was no longer holding proper charge. The battery problem was causing erratic behavior in multiple systems, especially affecting the start-stop functionality. The complete fix included: Battery testing and replacement, Electrical system diagnostic check, Reset of the engine control unit Total cost was 290 Euro, including parts and labor. Since the repair, the car battery has performed flawlessly and the unusual shut-offs completely stopped. Before suggesting specific solutions, could you share: Current battery age, Whether the starter motor makes any unusual sounds, If the engine start problems occur more frequently in cold weather, Recent electrical system changes or installations This information would help determine if your A3 is facing the same underlying issue as my A4 did.

Thanks for the details about a possible battery issue. I had my latest service at 149000 KM just 4 months ago. The starter motor does sound a bit rough lately and the engine stalling happens more frequently during cold starts. During the service they actually checked the battery but found it to be fine. However, the automatic restart system seems much more problematic now compared to before. One difference I noticed is that the warning lights stay on longer after each engine stalling incident. I checked the battery connections yesterday, they appear clean with no visible corrosion. The voltage reading shows 12.1V when idle, which seems a bit low. Could this point to a failing alternator rather than just a car battery problem?

Thanks for the additional details. Your voltage reading of 12.1V while idle is concerning, a healthy car battery should show around 12.6V when the engine is off and 13.5-14.4V while running. This does point toward potential alternator issues rather than just the car battery alone. My A4 actually showed similar symptoms before the complete diagnosis. While the start-stop system issues were initially blamed on the battery, the workshop found the alternator wasnt providing consistent charging. The rough starter motor sound you mentioned mirrors my experience exactly. Key points that suggest alternator trouble: Low idle voltage, Start-stop system malfunction, Persistent warning lights, Rough starter motor sound, Problems worse during cold starts The fix in my case required: Alternator replacement: 420 Euro, New drive belt: 45 Euro, System diagnosis: 60 Euro The eco mode features and start-stop system returned to normal operation after the repair. Engine start reliability improved dramatically, especially in cold conditions. Consider having the charging system thoroughly tested. The alternator output should be checked under various load conditions, as intermittent charging issues can be missed during basic testing.

Appreciate the thorough information about the alternator. This definitely aligns with my symptoms, especially the charging voltage patterns and start-stop problems. Just had the car checked by a mechanic who confirmed your suspicions, the alternator is indeed failing to provide consistent power output. Got a quote for the repairs: Alternator replacement: 395 Euro, New belt and tensioner: 85 Euro, Full system diagnostic: 70 Euro Going ahead with the work next week. The automatic restart feature has been particularly unreliable lately, and the car battery voltage keeps dropping below optimal levels during idle stop phases. Hopefully replacing the alternator will resolve both the eco mode glitches and the unusual engine stalling. Will post an update after the repair to confirm if this fixes the cold start issues and normalizes the starter motor behavior. Thanks for helping identify the root cause, looking back, the symptoms clearly pointed to charging system problems rather than just a weak battery.