Audi Electrical Chaos: Multiple Overvoltage Faults Found

I faced a very similar electrical issue with my Audi A4 2.0T (2006). Having some experience with car electronics, I initially thought the alternator failure was causing these problems, but it turned out to be more complex. The symptoms matched yours exactly, multiple electrical issues, car ECU logging overvoltage warnings, and unreliable cold starts. The battery voltage was fluctuating wildly, causing cascade failures across different systems. My workshop ran a complete electrical diagnostic scan and found that while the alternator was producing power, the car battery was severely degraded internally despite appearing fine on basic tests. This created a situation where the charging system was getting incorrect feedback, leading to voltage regulation problems. The fix involved: Complete battery testing under load, Electrical system diagnostic scan, Replacement of the faulty battery, System reset and adaptation Total cost was 290 Euro including parts and labor. Before suggesting specific solutions, could you share: Have you checked the battery voltage both at idle and under load? Are there any specific patterns to when the electrical issues occur? What voltage readings are you getting from the alternator? Does the problem worsen during cold or wet weather? This information would help determine if your issue matches the root cause I experienced.

Thanks for the detailed answer. My mileage is 27162 KM. After checking the battery voltage as suggested, I get readings between 13.8V and 15.2V at idle, which seems too high. Under load with headlights and AC running, it jumps above 15.5V occasionally. The issues definitely get worse in wet conditions, and multiple warning lights now flash out of nowhere on the dashboard. The high voltage spikes are concerning since they could damage sensitive electronic components. I will get the alternator voltage regulator tested first, since these irregular readings point towards car electronics issues beyond just a weak battery. The circuit protection should prevent these voltage spikes, so something is clearly malfunctioning in the charging system.

Thanks for the voltage readings. Those numbers confirm what I suspected based on my experience with the same issue. The power surge pattern you describe, especially hitting 15.5V under load, is a classic sign of a failing voltage regulator not properly controlling the alternator output. When my A4 showed these symptoms, the workshop found that excessive voltage spikes were bypassing the normal circuit protection, causing widespread electrical issues. The voltage regulator built into the alternator was the primary culprit, but the overvoltage condition had also damaged several electronic control modules. In my case, replacing just the voltage regulator did not fully resolve the electrical issues. The complete fix required: New alternator with built-in regulator (680 Euro), System-wide diagnostic reset, Verification of all affected control modules The car electronics are highly sensitive to overvoltage conditions. Since your readings show similar patterns to what I experienced, I strongly recommend getting this addressed quickly before the high voltage causes cascading failures in other systems. The correlation with wet weather often indicates deteriorated electrical connections allowing moisture ingress, which can worsen voltage regulation problems. Having the entire charging system inspected will help prevent further damage to sensitive components.

Thanks for the input. After getting my car properly diagnosed, you were right about the voltage regulator being the core issue. The alternator failure was causing these wild voltage spikes that overwhelmed the circuit protection systems. The workshop confirmed: Alternator voltage output fluctuating between 13.8V-15.5V, Voltage regulator showing clear signs of electrical issue, Multiple ECU faults logged from overvoltage events, Some control module damage from power surges The total repair cost was 890 Euro including: New alternator assembly with integrated regulator, Replacement of 2 damaged control modules, Full system diagnostic reset, Testing of all car electronics After the repairs, the electrical system is now stable with proper voltage readings. The unusual warning lights have stopped, and cold starts are reliable again. This case shows how a failing voltage regulator can cascade into much bigger problems if not caught early. Will mark this thread as solved since the root cause has been identified and fixed. Thanks for helping diagnose this tricky electrical issue.