Battery light came on and voltmeter reads slightly below 12V: what is going on?

[mshan]

I was running some errands today and when I started up car at one stop I noticed that battery light (rectangle with plus and minus on it) lit up and didn't go out.

Pulled out manual and it said it could be V-belt, battery, or something with electrical system.

That is when I noticed voltmeter was slightly below 12V.

Was able to get home and car seems to run normally, but wondering what it the problem, and how do I fix it.

Is it as simple as changing battery?

Any insights would be greatly appreciated!


1999.5 Audi A4 1.8TQ manual with ~59,000 miles on it
(timing belt etc. was changed several thousand miles ago)

 

[hanoverphist]

sounds more like charging system than battery to me

 

[marincounty]

Your alternator is probably toast.

 

[Gillbot]

Get your battery and alternator tested.

 

[mshan]

Can I take it to somewhere like Autozone and get battery and alternator tested?

Or do I have to got dealer?

Also, can I damage car by driving it, or can it suddenly just stop at any point?

What else could it be other than alternator?

I guess it also makes sense to just take it to dealer (there is one garage that maintains BMWs, but I don't know how willing they are to work on Audis).

 

[brblx]

parts store should have a hand-held tester, which will do a conductance test on the battery and check charging voltage.

it probably won't stop running, but it may not restart.

 

[mshan]

Did a quick search for "alternator" over at Audi World and found this: http://forums.audiworld.com/sh...6&highlight=alternator

Would alternator failure be something progressive (e. g. car just gets harder to start over time before it completely fails, or can it just completely fail?)

I am definitely going to get it fixed soon, but am wondering how much driving I can safely do in mean time (e. g. try going to Autozone or independent garage before having to resort to dealer).

 

[mshan]

Well, independent German import garage no longer has an Audi tech, so it looks like dealer.

 

[ViviTheMage]

Originally posted by: marincounty
Your alternator is probably toast.

Happened on my old 01 1.8t jetta.

 

[mshan]

How much should repair cost at dealer?

Audiworld thread to buy a rebuilt one (?), and 2 - 3 hours labor.

 

[SJP0tato]

Originally posted by: mshan
Can I take it to somewhere like Autozone and get battery and alternator tested?

Or do I have to got dealer?

Also, can I damage car by driving it, or can it suddenly just stop at any point?

What else could it be other than alternator?

I guess it also makes sense to just take it to dealer (there is one garage that maintains BMWs, but I don't know how willing they are to work on Audis).

Autozone and other parts stores have the equipment to run basic tests on the battery and alternator. Usually this is all that's needed 99% of the time, and it's free.

If the problem is the alternator, you're running on whatever charge is stored in the battery. Eventually you'll use up enough that the next time you go to start it there won't be enough power to turn the starter and you'll be stuck until you use jumper cables to "jump" the battery. Less likely is the car could stall out during driving because of lack of power.

Other than the alternator or battery it could be corrosion on the battery cables, loose connection to the battery itself, a loose ground wire, corroded wires leading to/from the alternator/battery.

 

[LTC8K6]

Hit Autozone / Advance Auto and let them test your charging system.

 

[mshan]

I assume Autozone and Advance Auto provide free service to hopefully sell something (battery mainly?)

Does it make sense to do this step first, or should I just go get robbed at dealer right away, particularly given SJPOtato's comment that I am probably basically running on whatever charge I have in battery now.

 

[SJP0tato]

Originally posted by: mshan
I assume Autozone and Advance Auto provide free service to hopefully sell something (battery mainly?)

Does it make sense to do this step first, or should I just go get robbed at dealer right away, particularly given SJPOtato's comment that I am probably basically running on whatever charge I have in battery now.

Hard to say. Knowing what dealers charge these days I'd chance going to the parts store first myself.

If you have a multimeter at home you can run a test too: Test the voltage across the battery terminals with the car turned off. It should read between 12 and 12.7 volts (higher is better).
Then with the car idling test the voltage again, it should read 13.5-15.5 volts.
Last have someone hold the engine rpms at 2000 in neutral, and test the voltage. It should read between 13.5-15.5.

If you're able to test all of these, write down the results and report back and I or someone else should be able to help you interpret what the numbers mean.

 

[LTC8K6]

Yes, the AZ / AA check is free.

 

[mshan]

I do have a multimeter (model DT830B), but can only do first two readings. Are these 3 steps what Autozone would do?

Do I set it at DCV 20 to get proper range on reading?

Also read somewhere while googling suggestion to take red positive lead off battery while car is idling and see if it stalls (presumably this means alternator is bad?)

 

[exdeath]

If you drive it, you risk stranding yourself and damaging either the battery or alternator if one or the other isn't part the problem.

Should be reading 12.6v when off, and around 14v when running and at least 13v+ running with lights, defroster, ac, stereo, etc. on. The progressive hard starts is a result of the battery slowly being discharged over time due to low charging system output.

For now, keep your battery on a trickle charger overnight. Measure the output at the alternator post directly instead of the battery post to rule out a faulty connection. Finally if you get a real tester and someone who knows what they are doing they can measure alternator output with a current clamp which tells the whole story.

 

[mshan]

I'm not too car savvy, so it sounds like I should take it to Autozone.

What sort of repairs short of replacing alternator itself are possible, and what is typical cost range? (and how many can autozone do themselves if I buy proper parts from them)?

 

[exdeath]

Originally posted by: mshan
I'm not too car savvy, so it sounds like I should take it to Autozone.

What sort of repairs short of replacing alternator itself are possible, and what is typical cost range? (and how many can autozone do themselves if I buy proper parts from them)?

Typical 100+ amp alternator on a newer car starts at $200+ for remanufactured. On a 4 cyl you shouldn't be charged more than 1-2 hrs labor.

Be wary of Autozone remanufactured units if you don't want to be making use of their lifetime warranty every 3-6 months. You get what you pay for when it comes to alternators and starters.

Removing and replacing the alternator is straight forward in most cases, if it's at the top front; disconnect battery, remove two connectors from alternator, remove tensionor bolt and belt, and remove another bolt and it comes right out.

You can also opt to rebuild the alternator yourself if you have some basic electrical skills. You can get a rebuild kit for < $100 that includes front and rear bearings, regulator and brushes, and 3 phase rectifier. The hardest parts are getting the pulley off (need an impact wrench or something to hold the pulley without damaging it while you turn the nut), and replacing the rectifier which has about half a dozen solder points.

You won't find an auto shop that will do this, as the labor cost would exceed the cost of replacing the whole unit. But a place like Autozone should be able to help you remove and install the alternator in the parking lot, it's really not any more complicated than removing a battery unless it's really buried.

 

[LTC8K6]

I just had an alternator rebuilt at a local alternator/starter shop for $80 with a 3 year warranty.

 

[mshan]

There looks like there is some sort of belt loose at left front of car (looking at engine from front), right behind passenger headlight area.

Read something about a sepentine belt in these Audis.

Could this be problem, and can Autozone replace it, or does dealer have to take front of car off to access area?

edit: started up car and realized that "belt" is just a cloth covered cable from some part of engine.

 

[mshan]

Also tried multimeter with engine off and on at idle:

18V (car off)

16V (car at idle)

no one to press accelerator to 2000 rpm for third reading.

 

[LTC8K6]

Do you have your meter on AC instead of DC?

The running reading could indicate you've lost a diode in your alternator, but the off reading is odd.

 

[mshan]

DCV and pulled the tips on metal parts of battery.

 

[mshan]

Anyone think it might be prudent to buy a car battery charger like this ( http://www.amazon.com/exec/obi...ATVPDKIKX0DER&v=glance ), and fully charging battery before attempting to drive to dealer (less than 10 miles away)?

Also, does an alternator fail all or nothing, or just gradually?

Initially, when I noticed light I had ac on; I turned it off and the voltmeter moved slightly higher (though still right under 12 V).

And does progressively sagging voltage means battery is getting more and more drained?