VW Taos Electrical Nightmare: Voltage Faults Explained

Having dealt with similar electrical gremlins on my 2021 VW Tiguan, I can share some relevant experience. As someone with moderate experience in car electronics repairs, these symptoms sound very familiar. The main issue turned out to be a failing car battery despite its young age. The faulty battery was causing irregular voltage spikes, which made the car ECU log those high voltage errors. The voltage fluctuations were affecting multiple systems, especially during cold starts. My repair process involved: Complete battery diagnostic test, Circuit protection system check, Testing of the voltage regulator, Full scanning of electrical system errors The workshop found that the battery had a defective cell, which was causing the erratic behavior. Total repair cost was 290€, including: New battery installation, System diagnostics, Clearing fault codes, Testing all affected systems To better assist with your specific case, could you share: Battery age and last replacement date, Whether you notice dimming lights or slow starter motor, Current voltage reading if you have access to a multimeter, List of specific error codes from your diagnostic scan The symptoms you describe strongly suggest a car battery issue, but knowing these details would help confirm if your situation matches what I experienced.

Just had the dealership check it, turns out the alternator failure was creating dangerous voltage spikes. They found the alternator was outputting up to 18V during operation, way above normal specs. The high voltage was overloading the car ECU and other electrical components. The fix involved replacing: Alternator unit + voltage regulator, Battery (damaged from voltage stress), Several blown fuses Total repair came to 1290€ but everything works perfectly now. No more electrical gremlins or error codes. Last service was at 126273km and they did a full electrical system diagnostic along with the repairs. For others seeing similar overvoltage issues, definitely get it checked quickly before it damages more components. Worth doing proper voltage testing rather than just assuming its a weak battery.

Thanks for the update on your Taos electrical issue. The alternator diagnosis matches what I initially suspected but wanted to rule out the battery first. My Tiguan actually showed very similar symptoms before eventually getting diagnosed with alternator failure too. The 18V output you mentioned is dangerously high, normal alternator output should stay between 13.5-14.5V. This kind of overvoltage can definitely cause widespread electrical system damage if left unchecked. The repair cost is in line with what I would expect, considering the extensive component damage from the voltage spikes. My alternator replacement ended up being slightly cheaper at 980€ since I caught it before it damaged the battery. From my experience, the voltage regulator integrated into modern alternators is often the failure point that leads to these dangerous overvoltage situations. The circuit protection systems can only handle so much before components start failing. Your advice about proper diagnosis is spot on. A voltage test during alternator operation would have quickly revealed this issue, potentially saving money on replacement parts that got damaged by the high voltage.

Thank you all for the help identifying the alternator as the culprit. After the repairs my Taos is running perfectly with no more electrical issues. Quick breakdown of what was done: Dealership found the alternator putting out dangerous 18V power surges that were damaging multiple systems. The car ECU was constantly logging overvoltage faults from these voltage spikes. Total repairs included: New alternator + built-in voltage regulator (780€), Replacement car battery due to voltage damage (320€), Various blown fuses and electrical components (190€) With parts and labor the final bill was 1290€. Not cheap but worth it to protect against more extensive electrical damage. The service included full diagnostics and the shop confirmed all systems are now operating at correct voltage levels. Key lesson learned: Any signs of power surge issues or high voltage warnings need immediate attention. Getting proper voltage testing done early can prevent cascading electrical failures. For others seeing similar symptoms, dont assume its just a weak battery, have the alternator output tested too. All systems working normally now at 126273km with no error codes. Thanks again for helping diagnose this tricky electrical problem.