VW Tiguan Multiple Electrical Failures Need Urgent Fix

Had the exact same electrical issues on a 2020 VW Golf TDI. The voltage regulator inside the alternator was failing, causing unstable voltage output across all car electronics systems. This triggered multiple ECU error codes and affected various electrical components. The high voltage spikes were slowly damaging the car battery, which explained the cold start problems. When tested, the alternator output fluctuated between 11.8V and 15.2V instead of maintaining the standard 13.8-14.2V range. The fix required: Complete alternator replacement with new voltage regulator, New car battery since the old one was permanently damaged, ECU reset to clear stored error codes This was a serious electrical issue that could have damaged more expensive components if left unrepaired. The unstable voltage puts extra stress on all electronic control units and can cause premature failure of sensitive components. The symptoms match perfectly, unusual electrical failures, battery problems, and ECU errors are classic signs of a failing voltage regulator. Best to address this quickly before it causes more extensive damage to the electrical system.

Thanks for sharing your experience. This seems exactly like what I am dealing with in my Tiguan. The unusual electrical failures and car ECU errors match my symptoms perfectly. The alternator test results you mentioned make a lot of sense given the issues I am seeing. Did you remember roughly how much you paid for the full repair? Also curious if you have had any recurring electrical issues since getting it fixed?

Since getting my Golf repaired last month, the overvoltage problems have completely disappeared. The circuit protection systems are now working normally, and all electrical components function as they should. The total repair cost was 290€, which covered diagnostics, replacing the faulty car battery that was heavily discharged, and resetting the car ECU. The alternator failure symptoms turned out to be caused by the degraded battery rather than the voltage regulator I initially suspected. The repair shop confirmed the battery had internal damage causing the unstable voltage readings. After replacement, all the electrical systems stabilized and the unusual faults cleared up. I have not experienced any electrical issues since the fix, no more error codes, cold start problems, or system malfunctions. Looking back, addressing this promptly was the right call to prevent potential damage to other electrical components. The high voltage fluctuations could have caused more extensive problems if left unchecked.

As a follow up to my initial post, I took my Tiguan to the repair shop yesterday after seeing the responses here. The mechanic confirmed similar voltage issues you all mentioned. The power surge problems were causing the unusual electrical failures. They tested the alternator and car battery, finding the voltage regulator was indeed failing. The output readings matched what others described, unstable voltage that was damaging other car electronics. The total repair came to 850€ which included: New alternator with voltage regulator, Battery replacement, Full diagnostic scan, Labor costs Just picked up the car today and all electrical systems are working perfectly now. No more unusual failures or error codes. The cold starts are strong again and everything feels stable. Really glad I got this sorted before it caused more damage to the electrical system. Thanks again for helping identify the issue. The symptoms matched exactly what you described and pointed me in the right direction for the fix.