Hi, I am not sure if this has been discussed anywhere else. But if anyone can give me a hint I would appreciate it. Yesterday my battery light came up as I was driving. I got home and measured the voltage with the car shut off, which is 12.5v; I started the car, measured the voltage, it is 11.5v. I took the battery to the shop and had them check it (they have the special equipment) and was told the battery was fine. So, my question is, would it be the alternator then? would it be something else possiblly? My car is a 99 A6 2.8, 179k. My battery is not the original battery, probably 3 years old (I've had this car for three years).

Would appreciate it if anyone can give an advice of what to do to determine the problem. Thanks.

Bo.

 

Sorry, I am moving ahead to do more diagnose myself. But I could not confidently determine where the alternator and voltage regualor are. Can someone help me at least to locate these two in the engine compartment? Thanks in advance.

 

Usually when the battery light comes on your looking at a bad alternator. The alternator is on the lower passenger side of the engine. It is most easily seen from the bottom of the car with the belly pan off. There is a wire that plugs into the back of the alternator. Not the large wire held on by a 13mm nut. Its a black plastic connector with either 1 or 2 wires. Disconnect it and measure the voltatge at that wire with the key in the on postition. You dont have to run the car to do this. If you have battery voltage or near that(it may be 9 or 4.5 v) your wiring to the alternator is most likly good. The next step would be to reconnect the black connector and check voltage from the big wire with the 13mm nut to gound. However this must be done with the engine running. If you get battery voltage there, you know you have a bad alternator. If you get between 13-14v there you have a bad alternator wire.

In any case im betting you have a bad alternator. The voltage regulator is internal to the alternator on this vehicle. As far as i know you can only replace the alternator and regulator as 1 unit. Hope that helps.

 

Thanks a lot for the advice. I'm trying to figure out how to takethe alternatoroff without taking the whole front end apart. I guess the first thing is to take the accessory belt off, but the space is very tight.

 

Very tight indeed. It is possible to take the alternator out with putting the front end of the car in service position, but its easier if you pull the front end out. Check out the timing belt writeups. All you have to do is pull the bumper off, loosen the radiator support bolts, and slide the radiator support(also known as the lock carrier) forward to give you plenty of room to make the repair. In any case the first step would be to remove the serpentine belt.

 

I'm sorry but what does it mean by "putting the front end of the car in service position"?

 

Basically you take the whole radiator and its support and slide it foreward. That gives you a good 3-4 inches bwtween the radiator and the front of the engine. It sounds like alot of work but its only a dozen or so bolts.

 

Thank you. Do you know if there is a write-up somewhere that I can follow? I changed my timing belt 6 months ago and really don't want to take the whole front end apart again within such a short period (maybe a year later would make me feel better). Really appreciate the information given so far.

Regards,

Bo

 

The nuts and bolts dont really require a writup. Two bolts hold the alternator in. Theres only two wires connected to it. Make sure you disconnect the battery before you remove the large alternator cable. The only hard part is snaking the alternator out. Just loosening the front end will give you plenty of space to remove the alternator. You wont have to disconnect the wires or remove the coolant hoses. Screw the long bumper bolts in one of the holes on each side where you remove the bolts that hold on radiator support. Then you can slide the whole frontend on those bolts without disconnecting everything.

 

If I understand you right, I still need to take the bumper off, right?