Alternator or voltage regulator or both? Or something else?

[eagano]

I was doing a few spirited pulls last night and all of a sudden the battery light comes on. Shortly after that, the whole cluster lights up and everything freezes. The speedo, tach, all the guages a frozen, the CEL is on as well as most of the other warning lights, and the brake like is flashing. I quickly pull over and power down, and fortunately the gauges reset.

I start it back up and everything is normal. After about five seconds the battery light is back on, and I see that it is pegged charging at 16v (the limit of the gauge). The car is running perfectly, but it seems to be overcharging so I make the short trip home and hope nothing burns up - the cluster locks up again. A few more restarts at home and the symptoms are always the same: volt meter goes to 12v after startup, then slowly climbs to 16v, then battery alarm goes off. This all takes about 10 seconds.

I've searched and found many threads on undercharging, just none on overcharging. I am guessing it is the voltage regulator since it is clearly charging. I don't want to replace the entire alternator as the regulator is much less expensive, but I know this is a 15 year old car.

Has anyone seen/solved a similar problem?

[SpooledUpS4]

My alternator just went and I'd just recommend going to autozone and have them test it. I installed a new voltage regulator and I'm going to see if that works. Otherwise I'll just buy one. The one I took off on the inside the copper looks burnt, so I assume it's fried. Don't know if that helped you, but that's my two cents.

[verstappen]

I was doing a few spirited pulls last night and all of a sudden the battery light comes on. Shortly after that, the whole cluster lights up and everything freezes. The speedo, tach, all the guages a frozen, the CEL is on as well as most of the other warning lights, and the brake like is flashing. I quickly pull over and power down, and fortunately the gauges reset.

I start it back up and everything is normal. After about five seconds the battery light is back on, and I see that it is pegged charging at 16v (the limit of the gauge). The car is running perfectly, but it seems to be overcharging so I make the short trip home and hope nothing burns up - the cluster locks up again. A few more restarts at home and the symptoms are always the same: volt meter goes to 12v after startup, then slowly climbs to 16v, then battery alarm goes off. This all takes about 10 seconds.

I've searched and found many threads on undercharging, just none on overcharging. I am guessing it is the voltage regulator since it is clearly charging. I don't want to replace the entire alternator as the regulator is much less expensive, but I know this is a 15 year old car.

Has anyone seen/solved a similar problem?

In my opinion, Just replace the whole unit. No point on getting to the alt just to replace the regulator, based on price of the part and work. And, if you want my .02 get a DB electrical alternator for about 90-100 they come tested with results sheet and good warranty. I have been dealing with them for a long time, never had a problem. Excellent parts. (as a matter of fact, I just installed a new db alt in my stg 3 b5s4 no problems at all).

[Bordom]

You can have your alternator rebuilt for about $150 with all new internals

Everything graciously mispelled by Android

[audacity]

yeah. if your gonna go the part store route, just replace the whole alternator. have yours rebuilt is what i would do. you can find them locally. you can have them wound for more amps as well like if you had a stereo system or something, we run high output ones on our trucks because of all the extra lights.

[Nichtknicken]

My vote is to find a local rebuilder as well. I've had nothing but terrible luck with chain store rebuilt alternators, not on the S4 specifically but I'm sure they don't go out of their way to use decent parts just for Audis. I gave up after having three die on my Rabbit GTI in 7 months and just paid for a factory Alt. no problem since.

[eagano]

Thanks everyone - I definitely would replace the alternator if it was undercharging or not charging at all. And after the feedback, it only makes sense to go with a local rebuild.

But it seems like mine is overcharging. I would guess that the alternator is working fine, just the voltage regulator that is out. Has anyone else run into an overcharging situation?

[eagano]

I wanted to close the loop on this for anyone that was searching and had a similar issue. It was indeed the voltage regulator. It was a $70 OEM part from GAP.
I probably could have replaced it from under the car with lots of swearing, but I ended up pulling the front clip to get to it.
The whole process was a great experience and I found some loose/missing screws so it was worth the effort (nothing important thankfully).

Quick summary:
- car was over charging
- key into ignition first position, voltmeter reads 12V
- start car, voltmeter moves to 14V, then slowly climbs to 16V after about five seconds
- cluster lights up like a Christmas tree
- all gauges freeze up even though car is completely driveable

Thank you German over-engineering.

I could have just replaced the whole alternator with a rebuilt one for not much more, but I like the idea of my original factory-intalled Bosch doing it's job.

Here is a pic of the old and new regulators. Audi part number 038-903-803-EX.
And I have to say, the guys at GAP are awesome, there were two different OEM alternators on this car (Bosch, Valeo), this part was used on tons of Audi/VW cars and superceded many times, but they came through with the right one.

[christianb5s4]

Good deal! The alternators on these cars seem to be pretty stout, vast majority of the issues alternator related are due to the voltage regulator. Another cause for voltage issues is the alternator cable harness corrodes over time and can cause many seemingly unrelated issues.

[S4_NE]

Both my S4 alternators took a dump at one point, My avant at 116,000 and the SDN at 85,000 both did the same just did not charge any more.

[dekkard]

eagano, thanks for the follow up!! I'm having the exact same issues as of this morning. But a question; I went to GAP and this is the only part that comes up for my 2001.5 S4: 038903803F - VOLTAGE REGULATOR (I'm guessing this is the old version?). When I plug in 038903803EX (new part #), it says it cannot verify that it will fit my car..

Also, cost of 038903803F (old) is $139 vs. $70 for the 038903803EX (new). My guess is that both will work but wondering what the differences may be? Thanks again!

[eagano]

eagano, thanks for the follow up!! I'm having the exact same issues as of this morning. But a question; I went to GAP and this is the only part that comes up for my 2001.5 S4: 038903803F - VOLTAGE REGULATOR (I'm guessing this is the old version?). When I plug in 038903803EX (new part #), it says it cannot verify that it will fit my car..

Also, cost of 038903803F (old) is $139 vs. $70 for the 038903803EX (new). My guess is that both will work but wondering what the differences may be? Thanks again!

I had the same problem struggling with part numbers, and ended up speaking with GAP on the phone. You are right, the 038903803EX is $70 plus a $15 core. It's a Bosch re-manufactured part which is why it is less expensive. I'm guessing that both work fine, but I'd rather save the $70.

Just make sure that you know which alternator is actually on your S4, because they came with both Bosch and Valeo from the factory.

[dekkard]

Thanks! I don't know why but I thought pre-2001.5 had the Valeo's and 2001.5+ had the Bosch's. Is that not correct? Thought I found a thread on that but will still confirm.

Edit: Also, what year is your car? Mine is a 2001.5.