97 A6 2.8 Avant C4 body

Yesterday my Audi stopped running when the battery got very low because it stopped charging. I figured it was the alternator so I replaced it with a used one and charged the battery.

My battery, charging system tester says that the battery is OK – even with load testing. But the voltage is only 12 when running. (should be 14V) Car starts OK and runs fine but the battery gage on the dash shows just under 12 V and it drops slowly.

The replacement alternator might be bad, but before I crawl under the car again I’d like to rule out a few other things.

The circuit from the battery to the starter and other electrical stuff looks to be OK so I’m questioning the wire to the alternator or the alternator itself.

From what I can tell the hot side battery cable connects to the stud in the engine compartment. From there the power goes to the starter and other electrical components. I also believe there is a wire between this stud and the alternator.

Is this correct and can I use the stud as common hot location?
Is there a fusable link in the wire from the Alternator?
Has anyone else had a problem like this and what did you do?


Any other help would be appreciated !


PS - I got the alternator out the bottom of the vehicle after moving a bunch of wires and the some water hoses. - I had to remove the front motor snubber and loosen the steel tubes that run across the front of the motor to get one hose out of the way.

 

There could be:

- Alternator + old battery problems - what could be the readings with new battery? Does the old battery hold the voltage?
- Alternator output voltage - was it measured?
- There should be charging relays that control the current and voltage. Do they function ok?

Do you have the wiring diagrams?

 

As far as I know the battery is OK - Yesterday it took a charge and tested OK at 12 volts - I then ran a load test and it still was OK. When I started the car the battery continued to read 12 volts so it was not getting power from the alternator. (should have been 14 volts)

I believe that the relays (control circuits) are internal to an alternator - not seperate like the old days with voltage regulators and generators - but don't know if there is anything additional on the Audi.

I have the Bentley manual with wiring diagrams for the vehicle but they are at home on my computer so I can't see them right now.


It started OK this AM but didn't show that it was charging (11.5 to 12 volts vs the expected 14 volts) so I left the car for my wife to use for her daily trip to the post office a few miles away. She called and said that it would not start this afternoon so there is probably a drain on the system.

 

Here's an update!

The first Alternator checked out bad at AZ. I'll now remove the second one and see if it is bad.

The Bently manual is just a little help. As I suspected the regulator is in the alternator and the battery, starter and alternator wires connect to each other in the engine compartment. It says the battery, jump start connector, and another wire connect at the engine compartment wiring junction, then the other wire, starter and alternator connect in the battery wiring harness, (Here's where Bentley sucks) but gives no clue as to where the engine compartment wiring junction box is. I'm sure it is burried somewhere in the mess of wires and hoses at the back of the motor...

I tried to find a diagnose procedure for the charging circuit and there is none... And I spent $100 for the Bentley CD!!!!

 

Another update –

Last night I charged the battery and began to remove the replacement alternator so I could get it tested. As I was working on it I found that the alternator was warm. I hadn’t started the vehicle or done anything to make it warm so there has to be a short of some type in the alternator. That is good news! The problem is not in the wiring. Next steps are to get another alternator and hope everything is OK.

I’m getting proficient at removing the alternator – skill I am not excited about possessing.

 

Last update - I hope --- Put a rebuilt alternator on the car last night and everything is OK.

Lesson learner -- Always have AZ check out a used alternator before installing it on the vehicle. It saves time and bruised knuckles.


PS during the last alternator install (battery disconnect) the damn sunroof retracted and would not go to the closed position. I turned off the ignition and used the hand crank to get it positioned correctly. When i turned things back on everything was OK.

 

In the spirit of full disclosure, I will add another update to the alternator sager.

After running OK for a few days - yesterday morning the car would not start. The battery was OK and the lights were bright, but when I turned the key there was nothing. Since I was had little time, I used my wife’s van to get to work. I asked her to call AAA to flatbed it to a trusted mechanic – Jim Price at Price’s Sunnycrest Garage in Newmarket NH. I figured that it was probably a bad starter.

A few hours later Jim called me and said that it seemed to be a bad ground and he thought the starter was OK. I turned out to be the ground wire between the chassis and the motor, although tight, was not making good contact.

Kudos’s to Jim Price. Instead of just changing the starter, he figured out what was wrong and it saved me a lot of time and money.

lessoned learned #2 - even if the ground wire looks good -- always clean the surfaces before tightening the bolts.

 

I envy you!
Having mechanic like this - honest and prudent is not much of a common these days

 

Lesson #3 If you have a DVOM always check the ohm readings and volt drop between the ground cable on the battery and the charge cable from the alternator to the battery before either replacing the alternator or starter. Most starter issues on audi's are ground connections.

 

Oh an upgrading the ground cable to a steel braided cable is a very good idea. I have done it for several people and they have reported better cranking, smoother idle, and even better fuel economy! I use steel braided ground cables on all my cars and i love em.