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The car is a 2013 Seat Mii with start/stop functionality.

The alternator is faulty as the output (measured at the alternator on an oscilloscope after the regulator) fluctuates between 3V and 14.5V in a random pattern. It should stay constant at 14.5V.

I've killed my battery due to undercharging through several weeks.

Is it the regulator (built into the alternator) or the alternator itself which is faulty ? Is it repairable ?

The alternator is a 110A BOSCH item with part number 04C 903 023D

  • poor signal from ecu? – Solar Mike May 22 '18 at 18:17
  • Welcome to Motor Vehicle Maintenance & Repair! – Pᴀᴜʟsᴛᴇʀ2 May 22 '18 at 18:23
  • Yes is is repairable but we have no idea what you skills are in repairing an alternator, best solution is to replace the alternator. – Moab May 22 '18 at 19:17
  • What happens if you disconnect the plug and run the engine at 2500 rpm? – Ben May 22 '18 at 21:55
  • @SolarMike what does the ecu have to do with this ? – Kelvin Wayne May 24 '18 at 9:50

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