Audi TT Battery Mystery: Sensor vs. Charging System

I had a very similar issue with my 2007 Audi A4 2.0T last winter. Having some experience with basic car maintenance, I initially thought it was just a battery issue, but vehicle diagnostics revealed it was more complex. The symptoms matched yours exactly, weak starts and flickering lights, even though battery testing showed normal voltage. After trying basic battery maintenance and cleaning the terminals without success, I took it to a workshop specializing in electrical systems. They performed comprehensive battery health checks and found the battery sensor was indeed defective, causing incorrect readings to the car's electrical system. The repair cost 315 Euro, which included: New battery sensor, Programming/coding, Full system diagnostic check The fix completely resolved the symptoms, and the car has been running perfectly since then. Before suggesting specific solutions for your TT, it would help to know: What engine variant do you have? Have you noticed any error messages on the dash? Does the problem occur more frequently when cold or after the engine is warm? Did you get any specific fault codes from previous diagnostics? This information would help determine if your issue matches what I experienced with my A4.

Last service was at 115000KM, and I really appreciate your detailed response. These battery and voltage sensor issues have been puzzling me for weeks. After checking more thoroughly, I noticed the problem occurs mainly during cold starts, and my onboard computer shows error code P0562. No warning lights on the dash, but the low voltage symptoms persist even after cleaning all connections. Vehicle diagnostics did show some irregular voltage patterns during cranking. Thanks for sharing your experience, the cost breakdown for your repair helps me understand what I might be looking at budget-wise. Would you recommend getting a second opinion from an electrical specialist before proceeding with the sensor replacement?

Thanks for the additional details, those symptoms and the P0562 code definitely align with what I experienced. The cold start issues and irregular voltage patterns during cranking were exactly what my A4 displayed before the repair. In my case, I actually did get a second opinion, and Im glad I did. The electrical specialist used advanced battery testing equipment that showed the battery sensor was sending incorrect signals to the power management system. This explained why the low voltage issues persisted despite having good battery readings. A key learning from my experience: the irregular voltage patterns during cold starts are a telltale sign of a failing battery sensor rather than just a weak battery. The car battery itself can test fine, but if the sensor isnt accurately reporting the battery voltage to the system, youll keep getting these symptoms. For reference, the entire diagnostic process at the electrical specialist cost me 85 Euro, which was worth it for the peace of mind before committing to the full repair. They identified the exact same issue as the first shop but provided more detailed testing data. Based on your error code and symptoms matching mine so closely, it does sound like youre dealing with the same battery sensor problem. The cold weather tends to make these symptoms more noticeable because the electrical system is under more stress during startup.

Appreciate your thorough input and sharing those repair costs. The detailed vehicle diagnostics information youve provided matches my situation perfectly, especially regarding the cold start behavior. Ill definitely follow your advice and consult an electrical specialist for a second opinion before proceeding with the battery sensor replacement. The fact that your symptoms cleared up completely after fixing the sensor is reassuring. Since my error code P0562 and the irregular voltage patterns match your experience so closely, Im feeling more confident about the repair direction. The 85 Euro diagnostic fee seems reasonable for getting certainty about the root cause. Ill schedule an appointment with an electrical specialist this week to run those additional tests. Would it be okay if I report back here with what they find? It might help others dealing with similar low voltage issues in their vehicles.