View Full Version : Erratic Voltage Problem

02-13-2015, 05:44 AM
2000 A4 Quattro 2.8 with 5 speed manual transmission. Yesterday my low battery light came on and went off several times in 50 minutes of driving. When the light was on the voltmeter showed about 12 volts (less after the engine ran off the battery only for a while). When the light was off the voltmeter registered a little over 14 volts. I replaced the battery early last fall.

So it seems like my alternator is dying. Since it has 223,000 miles on it I canít say Iím surprised. For this Bosch alternator I see the voltage regulator/brush assembly is an all-in-one affair. Before I order this part I wanted to see if itís possible I have another problem that I should check first. Getting that alternator out of there doesnít look like a lot of fun. Is there something else that might be causing this erratic operation? Please?

02-13-2015, 07:29 PM
You could take it to an AAP or Autozone and have them test it. I had the same thing happen a while back. Tried to rebuild the voltage regulator but had issues getting it back together. Ended up buying a new alternator since it didn't cost much more that just the voltage regulator. Mine is a 2001 but swap out would have been super easy if I realized the fan hub had holes to lock it. All you need to do is slide an allen into the hole, sit it in the casting then loosen hub nut. Then you can pull the long lower bolt out.

02-22-2015, 08:55 AM
So I was able to remove the back cover of my alternator with the alternator on the car and without removing the motor mount. Despite my Haynes manual and the online auto parts places telling me I have a Bosch alternator I actually have a Valeo. That was unfortunate, since Valeo uses Torx head bolts (Bosch uses Phillips head screws). Torx external sockets are not easy to come by. Plus, the Torx bolts are recessed into cylindrical chambers on the alternator coveróyou need either a small diameter Torx socket or a deep Torx socket. So it was a fiddly job, using inspection mirrors and working by feel. Removing the electrical connector wasnít easy, since itís been there 15 years. Although the brushes are not meant to be replaced, you can indeed replace them. I got a pair of brushes for $10 at a local auto electric rebuilder.

If you do have a Bosch alternator this would be a considerably easier job. Iím sure it would take much less time that putting the car in the service position and pulling the alternator.

Valuing my time at $0.25/hour I figure this job only cost me about $11,874.32!!