I have a 1999 A6 quattro with 180,000 miles on the odometer. Last night on my way home from work a red battery light came on in the instrument cluster. I checked the serpentine belt and it appears fine. When the light come on, the voltmeter will drop to the 12 o'clock position. When I drive a little ways the light went off and the needle went back to its normal position (2 o'clock).I stopped by an Advance Auto and had the battery checked & it's fine. The guy at the store sad he thought it could be a bad ground connection that was causing the light to come on & go off. I had the alternator replaced in October 2012.

Can anyone tell me what can cause this red battery light to come on in the instrument gauge? I'm 200 miles from home, so I called Bluegrass Audi in Louisville and will have her checked out Friday.

 

as soon as your alternator output slips below the 12v mark your battery light is coming on . i would say if your belt is not slipping your alternator is on its way .. Could be a ground but personally i feel "bad grounds" are one of the biggest myths on the internet .. if it is on and tight . they do not become "ungrounded.. but anyway , worth a check ..

 

Second. Unless you park your car outside and it rains/floods, highly unlikely to get a 'bad ground' for the alternator. One exception is people who remove their bellypan and then find everything in the engine compartment, especially down low, gets corroded and filthy.

 

Well I starred it up this morning and the drive to work was just fine. I've got an appointment at the dealership Friday morning I just don't wanna go in saying I think my alternator is going out. That's like opening your wallet and asking them to take your money.

Is there a way to tell if the alternator is bad?

 

If your battery light comes on while you are driving a C5 Audi, your alternator brushes are worn out and your alternator needs to be replaced...that's how I've always known.

Dealer won't tell you anything unless they experience the symptom while they have the car.

 

Quite likely, especially after 140K miles or so. I've generally replaced the VR and brushes after 140K miles on GP if I've had to pull the alternator for any other reason, like the @#$%@#$%W$ coolant transfer tube on 4.2 V8s.......

At that point you can assess the condition of the slip rings and feel the bearings for play by rotating the alternator shaft..it should turn smoothly and quietly with some drag....too easily the bearings are worn. Same thing with axial play, some is necessary, too much is again worn bearing, normally the one closest to the pulley, obviously the toughest one to replace.

A new alternator will often NOT have a pulley connected to it, just a bare shaft. Take off the pulley on the old alternator with an impact wrench..just hold the pulley with a rag or a strap wrench and the impact wrench will yank it right off. Assembly is the reverse...just be careful with the impact wrench...on mine I know where 80-90 ft lbs is from the adjustment screw (IR wrench) that I use to spin on wheel bolts before I manually torque the wheel bolts to spec. There is a torque spec for alternator pulley bolt/nut but you need a special tool to hold the shaft and torque the nut.

 

My car seems to be fine as long as the AC, lights, radio, exec. are off. I had the guys at AutoZone check it out and their machine said the Voltage Regulator is bad. Only problem is no one in Louisville, KY has one. I have a service appointment with Bluegrass Audi tomorrow. I'm gonna try to buy the part from their parts department and have my mechanic put it on when I get back home this weekend. Any idea what one costs? I was looking anywhere from $85-135 at the 3 auto parts places I checked (none were in stock, though).

 

They are telling you it's the regulator because the brushes are part of the regulator. You will not be able to buy this from Audi. You can try aftermarket, or just replace the whole unit, which I (still) recommend.

 

Well, I called the Audi dealer this morning & they didn't have the Voltage Regulator in stock, BUT they were kind enough to do a quick search on VW's parts site & a VW dealer in Clarksville, IN had one in stock. I picked it up for $140 (tax included). I then drove over to Bluegrass Audi and politely asked for an ESTIMATE on what it would take to install the part. I was told "we won't know until we look at it to see how long it will take". I said you don't know how long it will take you to remove the alternator and unscrew the old regulator and put the new one on? The Service Manager didn't know (which had me worried immediately because they should know basically everything the shop). He went into the service bay and asked one of the "technicians" and came back with an answer of 3 hours labor & $450! I felt like he was committing a Mugging right there in front of everyone in the Service Department. I told him "No thanks" and left.

I'm 200 miles from my regular mechanic, BUT my wife's mechanic is passing through Louisville, KY on his way to a fishing trip. He thinks he saw a video on YouTube that looks simple enough to do. Can it be done easily with tools that can be gotten at AutoZone/Advance Auto Parts OR should I wait for my regular mechanic?

Btw... the Vaelo alternator was replaced last October, which is why I'm not replacing the entire unit.

 

Oh yeah, the part was $180 at the Audi dealer & only $140 at VW.... What's with that???