VW Touran Charging System Problems, Full Diagnosis

I had a very similar voltage drop with my 2017 VW Tiguan and can share my experience (some basic car maintenance experience here). Initially thought it was just a dead battery, but the electrical problems kept getting worse. The headlights would dim, power windows became sluggish, and the radio would reset out of nowhere. The voltage regulator in the alternator turned out to be failing, which caused improper battery charging. Took it to a workshop where they: 1. Tested the electrical system completely 2. Confirmed both alternator issue and battery damage 3. Replaced the battery since it was damaged from improper charging 4. Checked all power supply connections Total repair cost was 290€ which included parts and labor. The fix resolved all electrical problems completely. Before suggesting specific solutions for your Touran, could you share: Current battery age, Whether voltage issues happen more during idle or while driving, If you notice any unusual alternator noise, Whether the battery warning light stays on after starting These details would help determine if your symptoms match what I experienced with my Tiguan or point to a different electrical problem.

My Touran just had its service last month. I tried measuring the battery voltage across terminals with a multimeter and got readings between 11.8V and 12.2V while running, which seems quite low. The voltage regulator test at idle showed inconsistent readings, suggesting this could indeed be more than just a battery issue. A proper voltage test across all circuits would help pinpoint if the alternator is failing to maintain correct charging voltage. From what I understand now, checking the alternator output and doing a full charging system diagnostic might be the best next step before replacing parts. Good point about checking battery age, mine is still the original from 2019, so it could be contributing to the charging system problems. I will make note of when the voltage drops occur most and listen for alternator noise before heading to the shop.

Thanks for sharing those voltage readings. Those values definitely point to charging system issues, very similar to what I experienced. A healthy battery should show around 13.8-14.2V while running, so your 11.8-12.2V readings indicate the alternator is not properly charging the battery. In my case, inconsistent voltage regulator readings at idle were also one of the key symptoms before the complete diagnosis. The unstable voltage output was causing the battery health to deteriorate, even though the battery was relatively new. Since your battery is the original from 2019, and considering the symptoms match mine almost exactly, I strongly suspect you are dealing with the same alternator voltage regulator failure I had. My repair involved: Complete electrical system diagnostic, Alternator replacement with updated voltage regulator, Battery load testing, Power supply connection cleaning The unstable charging damaged my battery beyond recovery, which added to the repair cost. Getting this fixed soon could save your battery from similar damage. Would recommend having the charging circuit fully tested. A proper diagnosis will show if the voltage drops are happening due to the alternator or if there might be other electrical problems causing the inconsistent readings.

Thanks for the detailed breakdown of what you found with your Tiguan. After checking my battery terminals again today and getting those concerning voltage readings, I believe you are right about this being more than a simple battery problem. The electrical symptoms in my Touran match yours exactly, especially the unstable voltage during idle. Looking at my readings between 11.8V and 12.2V while running, compared to the 13.8-14.2V you mentioned as normal, confirms I have a charging system problem that needs proper diagnosis. The original 2019 battery could be at risk if this alternator issue continues much longer. I will take it to the shop this week for a complete charging system diagnostic before any components get damaged beyond repair. Your repair costs of 290€ give me a good reference point for what to expect. Really helpful to know that thorough testing caught both the alternator voltage regulator failure and battery damage in your case. Will make sure they check all the items you listed, full electrical testing, alternator output, battery condition, and power supply connections. Thanks for helping me understand what I am likely dealing with. This will make the conversation with the workshop much more productive.