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battery light up

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battery light up - 10/23/2007 8:44:59 PM

wings7351

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Joined: 3/5/2007
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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.

Post #: 1

RE: battery light up - 10/24/2007 7:01:51 PM

wings7351

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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.

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Post #: 2

RE: battery light up - 10/24/2007 7:34:14 PM

dankhound

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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.

(in reply to wings7351)

Post #: 3

RE: battery light up - 10/24/2007 7:44:03 PM

wings7351

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Thanks a lot for the advice. I'm trying to figure out how to take the alternator off 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.

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Post #: 4

RE: battery light up - 10/24/2007 7:51:39 PM

dankhound

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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.

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Post #: 5

RE: battery light up - 10/24/2007 8:18:10 PM

wings7351

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

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Post #: 6

RE: battery light up - 10/24/2007 8:24:18 PM

dankhound

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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 a lot of work but its only a dozen or so bolts.

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RE: battery light up - 10/24/2007 8:39:05 PM

wings7351

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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

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Post #: 8

RE: battery light up - 10/24/2007 9:10:01 PM

dankhound

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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.

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Post #: 9

RE: battery light up - 10/25/2007 8:51:12 AM

wings7351

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

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RE: battery light up - 10/25/2007 8:23:22 PM

dankhound

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To put the radiator support in service position yes. Those two long bolts im talking about hold the bumper in in the front. They are behind the front lower side grills. They go up thru the bumper.

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Post #: 11

RE: battery light up - 10/26/2007 6:42:19 AM

wings7351

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Thank you very much. Really appreciate the help.

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RE: battery light up - 10/26/2007 9:40:02 AM

wings7351

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Just another quick question. Since I am taking the front end off anyways, should I change my starter at the same time? Or do I have to take the front end off when I need to change the starter?

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Post #: 13

RE: battery light up - 10/26/2007 8:03:52 PM

wings7351

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I was able to put the car in to service position, thanks the advice from dankhound. However I am stuck here. I took one tx50 bolt and one 13mm bolt off, the alternator does not seem to move. I can't see any other bolt on the alternator. Is there anything else I should take off?

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Post #: 14

RE: battery light up - 10/27/2007 8:36:58 AM

wings7351

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Ok, I tapped on the alternator and it was loosened. But now I am trying to figure out should it come out from the front or the back? Coming from the front seems to be impossible without removing the two pipes in front of it; coming out from the back seems to have more obstacles although there is room for it to move back a little bit. Can anyone that has done this job before give me an idea on this? (also the plug seems to be pretty hard to be removed too). Thanks in advance.

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Post #: 15

RE: battery light up - 10/28/2007 8:16:55 AM

dankhound

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Ive always taken it out the front. Is it possible to just lossen the brackets for the pipes and move them out of the way without disconnecting them?

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Post #: 16

RE: battery light up - 10/28/2007 8:24:39 AM

wings7351

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Thanks Dankhound. Did you mean the bracket right in front of the alternator? I did that. But it did not help a lot. I will try again. When you pulled it out, did you have to rotate it somehow?

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Post #: 17

RE: battery light up - 10/28/2007 9:23:59 AM

wings7351

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Ok, just took the bad boy out. Dankhound, I basically pulled harder to overcome the interference from the two steel pipes and really have to move the core a lot further than I original thought. The bumper bolt does not seem to be long enough for me in my case, maybe it is just because the orientation of the alternator when I took it out. The scary part to me just now was the flexible coolent pipe attached to the engine was squeezed by the alternator a lot when I pulled it out. Is it normal? Thanks a lot Dankhound, without your advice it would have taken me a lot longer and harder to even just take it out. I am trying to vision what should I do when I put it back. Regards.

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Post #: 18

RE: battery light up - 10/28/2007 9:30:13 AM

dankhound

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It certainly is a tight fit. Seems like everything is on these cars. Just look how tight the alternator was once you removed all the bolts. Your down there looking for hidden bolts and stuff. Only to find out there are none. Ive always wanted to removed the bolts and start the car with the belt on to see what would happen. I bet the alternator wouldnt even move. As long as you didnt cut the coolant hose it will be fine.

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RE: battery light up - 11/7/2007 9:01:01 PM

wings7351

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Dankhound, this post is just to let you know that I have completed my project. Thank you very much for your help!

Putting the alternator back was actually easier than I thought (maybe because the experience I had when pulled it out). The only trick in my case was that I had to install the 13mm bolt before installing the tx50 bolt, I tried the other way around but it just did not work. It took me some time to figure that out but after that everything was fairly smooth ( I did the timing belt half year ago so I know what to do to put them back).

Again, thank you very much! I found out you had been helping a lot of other people too.

And thank to all the people that are helping other people in this great forum!

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Post #: 20