RS3 Battery Sensor Issue Causes Cold Start Problems

Had the exact same symptoms on my 2021 RS4, which shares many electrical components with the RS3. With some experience working on Audi electronics, I can say battery sensor issues are more common than you might think. My vehicle diagnostics also showed normal battery voltage initially, but the battery sensor was sending incorrect signals to the power management system. This caused the slow cranking and dimming lights, despite the car battery itself being fine. Got it fixed at a workshop where they ran comprehensive low voltage system tests. The battery testing confirmed the sensor was misreading, causing the car to think it had power issues when it didnt. Total repair came to 315 Euro including the new sensor and programming. To properly diagnose this, could you share: Current mileage, When symptoms first appeared, If any warning lights are showing, Whether problems occur more during cold or warm weather, If you have any aftermarket electronics installed These details would help confirm if your issue matches what I experienced with my RS4.

Thanks for the detailed response. Just checked, my current mileage is 188056 KM and these battery issues started showing up after my last major service about 3 weeks ago. Symptoms mostly occur during cold weather and theres no aftermarket electronics installed. The voltage sensor readings from my last diagnostic scan were inconsistent, showing fluctuating values even when the battery health seemed normal. No warning lights on the dash yet. The car battery itself is still the original one from 2023, so Im wondering if a full battery replacement might also be worth considering alongside checking the sensor.

Thanks for those details. This really mirrors what happened on my RS4, especially the timing after service and cold weather correlation. Your fluctuating voltage sensor readings are particularly telling. In my case, the symptoms appeared about a month post-service. The voltage sensor was actually damaged during routine battery maintenance work. The car battery itself showed normal charge levels, but the faulty sensor kept sending incorrect low voltage signals to the system. Since your car battery is relatively new (2023), I would advise against immediate replacement. The original battery should easily handle several more years of service. Focus first on the battery sensor issue, as replacing a perfectly good car battery would be unnecessary expense. Here is what worked for my RS4: 1. Had a full battery charge test done first 2. Got the voltage sensor replaced 3. Had the battery management system reprogrammed Total repair time was about 2 hours and solved all starting and lighting issues. The sensor itself cost around 180 Euro plus labor. Worth every cent as it completely resolved those cold start problems and flickering lights. Would definitely recommend getting the sensor checked before considering any other battery maintenance steps.

Thanks for your informative answer. The inconsistent voltage sensor readings and cold weather correlation definitely match your experience. Ill hold off on replacing the battery for now since its still relatively new and focus on the sensor issue first. Just booked an appointment to have the voltage sensor tested and potentially replaced. The workshop quoted around 200 Euro for parts and labor, which seems reasonable based on what you paid. They mentioned theyll do a complete vehicle diagnostics scan and battery health check before proceeding with any repairs. Really appreciate the detailed breakdown of your repair process. Knowing that a similar fix resolved these issues completely on your car gives me confidence were heading in the right direction. Will update once I get the results from the battery testing and sensor inspection. Looking back, the timing of these symptoms appearing right after the service does suggest possible sensor damage during maintenance, just like in your case. Hopefully a straightforward sensor replacement will sort out these cold start and lighting problems.