Audi A4 Electrical Chaos: Aux Battery Mystery Solved

Having faced a similar situation with my 2011 Audi A6 (2.0 TFSI), I can share some experience as someone with moderate car electronics knowledge. The symptoms you describe match exactly what I encountered. The power management system was showing multiple faults, and the car electronics became increasingly unreliable. After initial diagnosis, my auxiliary battery tested weak, affecting the entire electrical system. The repair involved: Complete testing of power management system, Replacement of auxiliary battery, System reset and recalibration Total cost was 290 Euro, including parts and labor. The fix resolved all electrical issues and error messages completely. Before suggesting specific solutions for your case, could you provide: Engine variant of your A4, Current mileage, Duration of these symptoms, Any recent battery replacements, Specific error codes if available This information would help determine if your auxiliary power system issues mirror what I experienced, as battery-related problems can vary significantly between engine variants and usage patterns.

After seeing similar symptoms and fixes, I checked my service records (last maintenance at 34306 KM) and found that both my main and auxiliary battery have never been replaced since the car was new. The error messages and electrical issues began about two months ago. The error codes mainly point toward voltage drop problems in multiple systems. Based on the responses, I will have my auxiliary battery tested first, since thats often the root cause of these electrical gremlins on our platform. Thanks for the cost estimate. My local shop quoted 310 Euro for a complete auxiliary battery replacement with system recalibration, which seems in line with what others paid for similar battery failure repairs.

After our previous discussion about auxiliary battery issues, I can confirm that replacing both batteries proved to be the right decision in my case. When dealinwith voltage drop problems, addressing both the main and auxiliary batteries simultaneously often prevents future electrical malfunctions. I also had never replaced either battery before the issues started, and waiting too long led to more complex electrical problems. The low voltage condition from the aging auxiliary battery started affecting other systems, creating a cascade of error messages similar to yours. The 310 Euro quote for auxiliary battery replacement and recalibration is reasonable. In addition to my initial repair costs, I eventually spent another 200 Euro on a new main battery, which provided much better cold starting performance and eliminated remaining voltage fluctuations. The battery malfunction symptoms completely disappeared after replacing both units. Most importantly, the error memory stayed clear of any voltage-related codes. Consider having both batteries checked and possibly replaced together to avoid repeated visits to the shop. Since your service history and symptoms match my experience so closely, this comprehensive battery replacement approach should resolve your electrical system issues completely.

Thanks for the helpful advice. After having both batteries tested, it turns out both indeed showed significant wear. Just had both the main and auxiliary battery replaced yesterday for a total of 510 Euro including labor and system recalibration. The low voltage warnings and unusual electrical malfunctions have completely stopped. The car starts much stronger now, and all systems are working perfectly. The auxiliary power system diagnosis showed normal readings after the repair. For anyone searching with similar issues: If you have an older Audi with multiple electrical problems, definitely get both batteries tested. The voltage drop from aging batteries can cause numerous seemingly unrelated issues. In my case, replacing both batteries and having the system properly recalibrated fixed everything. Really glad I asked here before spending money on diagnosing other potential causes. The battery replacement costs were reasonable considering it solved all the problems.