Audi S3 Battery Sensor Issue Drains Power System

I had a very similar issue with my 2008 Audi A3 2.0T. As someone with some experience in basic car maintenance and battery-related problems, I understand your concern about replacing parts without being certain. The symptoms you describe match exactly what I experienced, weak starts and dimming lights. Initially thought it was a battery health issue, but since your battery is new, the battery sensor is likely the culprit, just as it was in my case. My workshop performed vehicle diagnostics and confirmed the battery sensor was sending incorrect voltage readings to the car's computer. The repair included: Complete sensor replacement, System recalibration, Battery health verification Total cost was 315 Euro including parts and labor. Since the fix, all low voltage symptoms disappeared completely. Before suggesting specific solutions, could you share: Any error codes from diagnostics? Does the battery warning light come on? Have you noticed issues with other electrical components? What type of battery maintenance have you performed since installation? This information would help determine if your issue mirrors mine and whether the sensor replacement is the right solution.

I had a very similar issue with my 2008 Audi A3 2.0T. As someone with some experience in basic car maintenance and battery-related problems, I understand your concern about replacing parts without being certain. The symptoms you describe match exactly what I experienced, weak starts and dimming lights. Initially thought it was a battery health issue, but since your battery is new, the battery sensor is likely the culprit, just as it was in my case. My workshop performed vehicle diagnostics and confirmed the battery sensor was sending incorrect voltage readings to the car's computer. The repair included: Complete sensor replacement, System recalibration, Battery health verification Total cost was 315 Euro including parts and labor. Since the fix, all low voltage symptoms disappeared completely. Before suggesting specific solutions, could you share: Any error codes from diagnostics? Does the battery warning light come on? Have you noticed issues with other electrical components? What type of battery maintenance have you performed since installation? This information would help determine if your issue mirrors mine and whether the sensor replacement is the right solution.

Thanks for the response. The mileage is 14954 KM and last service was done during the battery replacement 6 months ago. A battery testing session with my multimeter showed 12.1V when idling, which seems a bit low. Will check all ground connections and clean terminals before proceeding with any sensor replacement. The battery warning light does flicker occasionally, especially during cold starts. No other electrical components show issues so far. Did your battery voltage readings match these values before fixing the sensor issue?

Thanks for the response. The mileage is 14954 KM and last service was done during the battery replacement 6 months ago. A battery testing session with my multimeter showed 12.1V when idling, which seems a bit low. Will check all ground connections and clean terminals before proceeding with any sensor replacement. The battery warning light does flicker occasionally, especially during cold starts. No other electrical components show issues so far. Did your battery voltage readings match these values before fixing the sensor issue?

Thanks for providing those details. Yes, my voltage readings were very similar, I was getting around 12.2V at idle before fixing the sensor, which is indeed low. A healthy system should show around 13.5-14.4V when running. After checking my service records from that time, my battery testing showed these values: Cold start: 11.9V, Idle: 12.2V, 2000 RPM: 12.5V These readings were caused by the faulty voltage sensor sending incorrect data to the charging system. The alternator wasnt receiving proper signals to maintain optimal charging. Similar to your case, my battery warning light would flicker during cold starts. Before replacing the sensor, I also cleaned the terminals and checked grounds, but it didnt resolve the issue. The battery health was good, but the system wasnt properly regulating the charging cycle due to bad sensor data. Your symptoms align perfectly with what I experienced. Since the battery is new and youre seeing similar voltage readings, a faulty sensor is likely causing your charging system issues. The occasional warning light matches the pattern as well. Would recommend having a professional run a complete charging system diagnostic to verify the sensor is the source before replacement.

Thanks for providing those details. Yes, my voltage readings were very similar, I was getting around 12.2V at idle before fixing the sensor, which is indeed low. A healthy system should show around 13.5-14.4V when running. After checking my service records from that time, my battery testing showed these values: Cold start: 11.9V, Idle: 12.2V, 2000 RPM: 12.5V These readings were caused by the faulty voltage sensor sending incorrect data to the charging system. The alternator wasnt receiving proper signals to maintain optimal charging. Similar to your case, my battery warning light would flicker during cold starts. Before replacing the sensor, I also cleaned the terminals and checked grounds, but it didnt resolve the issue. The battery health was good, but the system wasnt properly regulating the charging cycle due to bad sensor data. Your symptoms align perfectly with what I experienced. Since the battery is new and youre seeing similar voltage readings, a faulty sensor is likely causing your charging system issues. The occasional warning light matches the pattern as well. Would recommend having a professional run a complete charging system diagnostic to verify the sensor is the source before replacement.

Thanks for sharing those voltage readings and the detailed explanation of your experience. These numbers definitely help confirm my suspicions. My situation seems nearly identical, the flickering warning light and low battery voltage readings match exactly what I experienced. Will follow your advice and get a full charging system diagnostic done first. The low voltage readings during idle are concerning, but at least I know the likely cause now based on your experience. Cleaning the ground connections and terminals is a good first step for basic battery maintenance, but I suspect youre right about the sensor being the root cause. The fact that your repair resolved similar symptoms gives me confidence about the path forward. Just booked a diagnostic appointment to verify the sensor issue before proceeding with replacement. The 315 Euro repair cost seems reasonable if it fully resolves these battery voltage problems. Will post back with results after the diagnostic check and repair. Knowing someone else successfully fixed these exact symptoms with a sensor replacement is really helpful.

Thanks for sharing those voltage readings and the detailed explanation of your experience. These numbers definitely help confirm my suspicions. My situation seems nearly identical, the flickering warning light and low battery voltage readings match exactly what I experienced. Will follow your advice and get a full charging system diagnostic done first. The low voltage readings during idle are concerning, but at least I know the likely cause now based on your experience. Cleaning the ground connections and terminals is a good first step for basic battery maintenance, but I suspect youre right about the sensor being the root cause. The fact that your repair resolved similar symptoms gives me confidence about the path forward. Just booked a diagnostic appointment to verify the sensor issue before proceeding with replacement. The 315 Euro repair cost seems reasonable if it fully resolves these battery voltage problems. Will post back with results after the diagnostic check and repair. Knowing someone else successfully fixed these exact symptoms with a sensor replacement is really helpful.