View Full Version : Problem with Battery or Alternator? Please Need to identify problem asap

12-10-2010, 06:14 PM
Problem with Battery or Alternator?

Battery light is on for like 15 miles now and high beam almost dead, and I can start the car fine. Battery is 7-8 years old.

I would like to check alternator first - can I just remove positive battery cable when car is running? Usually if the alternator is bad car should stall. I did this test with different car but not the Audi.

1) Can somebody confirm that this is the way to quick test of faulty alternator??

2)I also have Vag-com, but I dont know where to check in vag-com for alternator voltage?

This is for A4 99.5 2.8 30V AHA


12-10-2010, 06:45 PM
7-8 years is pretty damn old for a battery, just saying.

12-10-2010, 07:22 PM
The best way to check the battery and charging system is with a load testing machine which also measures current flow. I recommend you have it checked. Autozone or Advance Auto will also do this for free. Pep boys probably will as well, but I'm not as familiar.

The most popular industry tool for this is the "VAT 40".

However,the car should run with battery disconnected. If it won't, the alternator is most likely faulty. Just because it passes that test, though, does not mean it is ok. It could be only providing a very weak charge such that the battery will slowly drain while driving with high electrical load (headlights, etc).

12-10-2010, 08:24 PM
I just checked - car stall with battery (terminal -) disconnected - so that mean that I have to replace alternator? right, just want to make sure - before I take the front out

12-10-2010, 10:47 PM
It could just be that the brushes in the alternator are worn out. You might be able to replace them without removing the alternator. I don't remember how much room you have on a 2.8, but I'd look into that first. I know removing the 2.8 alternator is a bit more work than the 1.8T.

12-11-2010, 06:57 AM
just in case, do you know where I can buy those brushes for the alternator?

12-11-2010, 11:45 AM
If it's a Valeo, I do. If it is a bosch, I haven't done one of those recently, so I'm not sure.

Here's my Valeo DIY:

12-11-2010, 12:24 PM
Great write up!
I have exactly the same alternator like on your picture-Valeo

More info: One week before Alternator failed there was some noise was occurring between when the engine was cold, when its hot there was no noise - sound looks like serpenter tensioner failing(I still remember sound before I did TB 2years ago). Then yesterday battery light came on, and now I hardly can start - Vag-com shows 11.2V.
My question is:
1) how do I know if the problem with alternator and Not the voltage regulator itself? (there were no issue with battery charging before).
2) where did you order Voltage Regulator for Valeo on Audi M521 Transpo, part M521?

12-11-2010, 03:21 PM
You can inspect the brushes. You can kind of tell if they are so short they aren't making good contact anymore. If that is the case, highly likely it is just the brushes. If the brushes look fine, then your problems may be elsewhere. I did go over testing the rotor in the DIY. That was the failure mine had: open circuit rotor winding. Funny, mine had some clicking kind of noise in the days before it failed as well. Mine stopped charging while driving for 10 minutes, then came back to life.

I would inspect the brushes and test the rotor before buying any parts. In my case, I got a junkyard alternator for $35 and put new brushes into it before installing it (they were pretty worn). I made sure to get a Valeo unit from the junkyard so I would have spare parts.

I ordered the M521 from a local alternator/starter rebuilder.

12-11-2010, 03:30 PM
"mine had some clicking kind of noise in the days before it failed as well." - I had exactly the same sound

12-11-2010, 03:32 PM
Minutes before the failure, the clicking seemed to get a bit louder as I could here it in the car, but just barely. Click click click, I brushed it off as a rock stuck in the tire or something and few minutes later I lost the charging system.

12-12-2010, 03:14 PM
Anybody from New York or Westchester(NY state) know any junkyard where I can buy alternator ?