emptyo

Hi all,

I have a 2000 A4 1.8 T. Lately, and with no warning, the charging system will stop working and my voltage will slowly drop from 12V to undriveable. Unexpectedly, it will all of a sudden start charging again, but will not charge when I park the car and start it back up. Obviously a pain in the *** to diagnose. Anyone seen this before?

Thanks,

Michael

turbo510

Could be a bad voltage regulator, the brushes will wear out.

emptyo

Thanks. Any idea how I test for something like that?

turbo510

The brush assemly is under the plastic cover at the rear of the alternator. If you find the brushes worn to the point that there is very little spring force pushing them against the copper slip rings, then the brush/regulator needs to be replaced. If they look OK, then you could take the alternator to one of the auto parts places that checks for free. Now if it works good there, maybe there is a defective connection between the alternator and battery.

o_a_ravi

I also have the same problem on my 2.8 V6 Motor. As the user Emptyo mentioned above, the symptoms are same.

Here are my repair details -

1. Changed the Alternator & Battery, since the alternator was reported to be weak.

2. 2nd Alternator also had the same charging issue, (voltage dropped below 12) quite often. So the alternator still under warranty was replaced with BOSCH 120 Amps

Now I still see this issue intermitted, but not that frequent. But definitely there appears to be a problem.

One more alternative fix, I found to be work is - When the voltage drops 12 or below 12. I just turn off the ignition completely, and after a few seconds, if turned back on it runs normally (voltage at around 12.6 - 13+)

Now talking to my mechanic we think as follows -
1. Ignition Switch issue ?
2. May be some relay (Load or PNP Relay)is dying making a bad contact
3. Is the voltage reference wire from Battery to ECU/Instrument cluster may be bad ?

But these are just our wild guesses.

Can somebody share your thoughts on this please ? Its really an annoying issue

turbo510

Your "fix" is not really that, and likely won't work after a while.

The voltage reference is built into the voltage regulator, which is installed on the rear-end of the alternator. Neither the ECU, instrument cluster, or ignition switch should have any effect on the charging voltage. By the way, 12.6 is really on the low end for charging, which shoud run up to around 14.5 Volts or thereabouts. I'd check the voltage right at the alt's output post, referenced to the alternator frame, and see if you are getting the same voltage between the battery posts.

Pariah819

Hello I know this thread is kind of old, but I am having the exact same problem on my 1999 Audi A4 2.8L. For several months the charging system would drop in and out. It was always on more than off and didn't seem to ever drain the battery so I kept putting it off. Last week though I replaced the ECT Sensor (because it got cold out and the car didn't want to start), and while that fixed my cold start issue the charging system has completely given up. Initially I thought that perhaps I bumped whatever was intermittent before and now its no longer intermittent. So I looked over all the wiring where I was working and it seemed good. So then I grabbed the old multi-meter and measured the alternators output post to chassis. It read 0.002V, obviously not good. So has my alternator given up and its just a coincidence that I just worked on the car beforehand? Is there anything else that I can check? While under the car it did seem like the brushes in the alternator we kind of loud, or at least louder than I thought they should be. If it is the alternator or the voltage regulator do both of these require the front end to be put in "service position" to fix?

Sorry for the long post but any help is greatly appreciated...

Pariah819

Any opinions or suggestions at all? It's about 15 degrees F here this week and I haven't been able to decide if I want to take on this project in my unheated garage or shell out the money for someone to fix it. I'm actually limping the car to work and back right now by charging it with a battery charger for a few hours every night.

Pariah819

Well on my drive to work this morning, all the sudden the alternator started charging again. This time it seemed to behave much differently than before. It would only charge if the engine RPM's were over 2k. It did that for most of my drive to work until about 2 mins out then it stopped working again. To me this seems less like a wiring issue and more like an alternator issue so I am going to get it replaced.

Thanks everybody for... well... nothing LOL

Smurfturd

I am having the exact same issue on my 2001 2.8L. If i have the lights and A/C off it sits at 12V just fine, otherwise it slowly dies out until the entire electrical system goes dim (over the course of an hour drive through traffic).

Please let me know how you proceed and if it fixes the problem. I have my front clip off right now about to pull the alternator.