VW Sharan's Voltage Gremlins: Beyond Battery & Alternator

I had a very similar issue with my VW Touran 2.0 TDI from 2004. Having some experience with electrical issues in VAG vehicles, I first suspected the alternator but it turned out to be more complex. The symptoms matched exactly, multiple voltage-related error codes, weak starting despite a new battery, and unusual electrical glitches. The voltage regulator inside the alternator was causing power surges throughout the electrical system, which explained the scattered malfunctions. My workshop performed systematic testing: 1. Full battery load test 2. Alternator output measurement 3. Circuit voltage testing at multiple points 4. Ground connection inspection The diagnosis revealed a heavily discharged battery due to the faulty voltage regulator. The constant power surges had damaged the battery cells. The total repair came to 290€ including a new voltage regulator and battery reconditioning. To properly diagnose your case, could you share: Exact engine variant, Battery age and type, Whether alternator warning light appears, If electrical issues occur more during idle or driving, Current voltage reading if you have a multimeter This information would help determine if your symptoms align with what I experienced and point toward the most likely solution.

Thanks for the details about voltage regulation problems. Just had my car serviced at 20107km last month, and they did a full electrical check but clearly missed something. The workshop initially thought it was just a weak car battery, but these power surges keep happening even with the new one installed. The high voltage spikes during normal operation match exactly what you described with the voltage regulator. Did your circuit protection system show any signs of damage when they diagnosed the alternator issue? The repair cost you mentioned is actually lower than what I was quoted for a full alternator replacement. Would appreciate if you could share the testing values they found during your diagnosis, might help confirm if I'm dealing with the same electrical issue before spending money on parts.

Thanks for the follow-up about your electrical issues. After my voltage regulator repair, I actually had the workshop check all circuit protection components because I was concerned about potential damage from the power surges. The testing values from my diagnosis showed: Battery voltage at idle: 14.8V (should be 13.8-14.4V), Peak voltage spikes reaching 15.2V, Resting battery voltage: 12.1V (indicated weak charge) The car ECU monitoring showed the voltage regulator was allowing dangerous spikes above 15V, which triggered the overvoltage protection circuits. This matches your symptoms perfectly. Importantly, my circuit protection components survived without damage, though the battery capacity was reduced. The repair cost was reasonable because we only replaced the voltage regulator unit instead of the entire alternator assembly. Most workshops default to complete alternator replacement, which explains your higher quote. The regulator itself is the usual failure point in these VAG engines. My advice would be to insist on voltage regulator testing before accepting a full alternator replacement. The electrical issue symptoms you describe are textbook voltage regulator failure, especially with the new battery still showing problems.

Thanks for the thorough explanation of your voltage regulator repair experience. The testing values you shared definitely match what I'm seeing in my car. Just had my mechanic check the readings today: Idle voltage fluctuating between 14.7V and 15.1V, Battery resting at 12.2V, Unusual spikes hitting 15.3V during normal operation The overvoltage protection in the car ECU keeps triggering exactly as you described. Good to hear your circuit protection components werent damaged, thats been a major concern since these electrical issues started. Will definitely have them test the voltage regulator separately before replacing the whole alternator. The car electronics are obviously being stressed by these power surges, but at least the fix might be simpler than initially quoted. Going to schedule the repair next week and request specific voltage regulator diagnostics first. Really helpful to compare the actual testing values, gives me more confidence in pushing back on the full alternator replacement quote.