RS3's Mystery Electrical Gremlins Need Urgent Fix

Had similar symptoms with my 2015 S3 last winter. Started with dim lights and slow cranking, then progressed to unusual electrical glitches in the infotainment system. The low voltage issue turned out to be more complex than just a bad battery. After proper diagnosis, the problem was traced to both a failing voltage regulator in the alternator and corroded battery terminals. The voltage regulator wasnt providing consistent charge to the battery, while the poor terminal connection made the existing battery health issues worse. The alternator issue was serious since it could have left me stranded anywhere. When testing showed the alternator output was fluctuating between 12.2V and 14.8V (should be steady around 14.4V), it confirmed the voltage regulator failure. Key diagnostic steps that revealed the problem: Full battery load test, Voltage drop test across terminals, Alternator output testing at different RPMs, Testing all main ground connections The repair required: New alternator assembly, Battery terminal cleaning and replacement, New battery (the old one was damaged from irregular charging) Worth getting these specific tests done rather than just a basic charging system check, as basic tests can miss voltage regulator problems.

Thanks for sharing your story. Going through something nearly identical with my RS3 right now. Ended up being a cascade of electrical problems starting with the alternator. Really interested to hear what your repair bill came to and if youve had any other voltage issues come up since the fix? My mechanic is quoting steep prices and Im trying to gauge if its reasonable. Dealing with similar battery voltage fluctuations, and those voltage drop symptoms you mentioned sound exactly like what Im experiencing. The irregular charging pattern is definitely concerning. Been keeping close tabs on the battery health with a multimeter since the first signs showed up.

Thanks for asking about the follow-up. After replacing the alternator, cleaning the terminals, and installing a new battery, my power supply issues were completely resolved. The voltage regulator now maintains steady output, and the battery terminal connections are solid. The total repair came to 290 Euro for diagnosing and fixing the heavily discharged battery system. This included a thorough check of all electrical components and replacement of the necessary parts. The undervoltage detection warnings that kept popping up have completely stopped. The battery voltage now stays consistently where it should be, no more fluctuations or irregular charging patterns. Been monitoring the battery health regularly and everything has remained stable for months. The investment was worth it to prevent potential electrical system damage and avoid getting stranded. When dealing with complex electrical issues like this, proper diagnosis and repair by a qualified technician usually saves money in the long run compared to replacing parts one at a time hoping to fix the problem.

Took the car to a new mechanic yesterday after reading about your experience. They did a full electrical diagnostic and found almost identical issues, failing voltage regulator and corroded terminals affecting the charging system. The battery voltage was all over the place, just like you described. They quoted 320 Euro for the complete fix including parts and labor, which seems fair based on your repair costs. Went ahead with the full service, new alternator, terminal replacement, and fresh battery since the old one was toast from the irregular charging. The shop did great work. All electrical systems are running perfectly now. No more dim lights or hard starts. The steady voltage readings from my multimeter confirm the charging system is working like it should. Such a relief to have this sorted before getting stranded somewhere. Thanks again for sharing those specific symptoms and tests. Really helped me communicate the issues clearly to the new mechanic and get an accurate diagnosis right away.