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Old 12-10-2010, 01:12 PM   #1
got_e46
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Diagnosis Time - Battery, Alternator or Voltage Regulator?

Already poked around about 2 dozen threads with Battery/Alternator/Voltage Regulator in the title. Some info was good, as far as testing each component while other information just seemed of opinion and not fact.

The car is a 2002 325ci with 80.1k on the clock as of this morning. In the year and a half that I have owned the vehicle, I have never changed the battery, alternator etc. My trusted mechanic is out of town for a few weeks so im turning here before I take it to a different dude.

Yesterday evening after getting off work, I noticed while starting the car that all the lights dimmed and the car clicked several times and then finally turned over. Today, I went to Advance Auto and had the battery tested, read 11.6 volts. The box the guy used didnt say "bad battery" or anything, and he assured me the battery is fine.

Last night, the engine wouldnt turn over at all, so I had to put it in reverse and do a rolling start to get the thing running. While doing research here, I ran across a thread that said to drive the car for 20-30 minutes. I went up and down the beltway at 3 am with no one on the road at 60 miles an hour and got back home in about 35 minutes.

To test whether this worked, I turned the car off and then turned it on, turned it off, turned it on. I did this a total of six times until the engine refused to turn over again.

So the battery was tested, with low voltage. It seems like the alternator is partially working? Could it be that the batter is not getting enough charge and the voltage regulator is the issue?

I will be glad to answer any questions and follow procedures to figure this out. Thankfully, its a weekend and not a Monday.
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Old 12-10-2010, 01:21 PM   #2
ixtoxi
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I'm betting it's the battery if it the original.
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Old 12-10-2010, 01:30 PM   #3
got_e46
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It definitely could be. The guy said the battery was fine, just needed to charge - which automatically made me think alt/volt. I dont mind changing the battery, lets get some more responses so I can make an informed decision.
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Old 12-10-2010, 01:44 PM   #4
jcns
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get a voltmeter.
start the car, and check the battery voltage; if it reads at least 14v it's charging fine and it's probably not your alternator.
If the voltage jumps up and down (it's not steady), it's likely the voltage regulator.
At 11.6v, your battery is border line bad. I bet you that if you don't fix the problem, after a few more days of driving/starting the battery will be done.
As for driving 20-30 min to charge battery; this used to work in older cars when the alternators were overbuilt(more than the car needed). Modern cars(for the most part) come with an alternator just "big enough" to keep the battery running and alive.
Also once the battery is bad(damaged), it will charge but it will NOT hold a charge.
Good luck
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Old 12-10-2010, 02:08 PM   #5
got_e46
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Thanks jcns, that makes much more sense.

I'll get a voltmeter after work, should I read voltage from the battery or the terminal under the hood? I read mixed opinions over that as well.

So points to note -

14v, charging and fine (not alternator)
Voltage fluctuation (likely voltage regulator)

Which leaves the battery.

Sounds like a solid plan so far.
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Old 12-13-2010, 12:05 AM   #6
got_e46
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Battery was the issue. Changed the battery and after two days of testing with the voltmeter, all seems to be well. Thanks for the help guys!
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Old 12-13-2010, 12:14 AM   #7
//TRD power
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11.6V is no where near good. A good battery reads ~12.1V

Quote:
Originally Posted by got_e46 View Post
Thanks jcns, that makes much more sense.

I'll get a voltmeter after work, should I read voltage from the battery or the terminal under the hood? I read mixed opinions over that as well.

So points to note -

14v, charging and fine (not alternator)
Voltage fluctuation (likely voltage regulator)

Which leaves the battery.

Sounds like a solid plan so far.
You don't need a separate volt meter, use the hidden feature in the lcd screen on the ODO for your volt meter and see the readings with the car off, on, and off again.
I can bet you definitely need a new battery, but worst case scenario, it was also a bad alternator causing the battery to go out, that's why you need to read the volts with the car on as well.

Link for accessing your hidden tools:
http://forum.e46fanatics.com/showthr...ht=easter+eggs
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Last edited by //TRD power; 12-13-2010 at 12:19 AM.
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