Charging system light

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mcahn
Posts: 226
Joined: Mon Apr 20, 2009 4:36 pm

Charging system light

Post by mcahn »

Hi all,

In my son's 2003 330ci, five-speed manual, 134,435 miles, the charging light (a battery symbol) on the dashboard is flickering. My local mechanic says that the alternator might be going bad, but it's still charging normally, so they suggested "keeping an eye on it". My question is -- how will this behave when it fails -- the light will stay on, so I'll know it's time to replace the alternator? Or, it'll stop charging but still be drivable, but won't start? Or it won't be drivable?

And how likely is it that the problem is the alternator? The alternator is original as far as I know, so I wouldn't be surprised if it failed. Would you suggest replacing the alternator before it fails?

Any advice appreciated,
Matthew

m20power
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Re: Charging system light

Post by m20power »

Simple tests will inform...measure battery voltage with car not running to get state of charge. Then, start car and measure voltage across battery showing alternator output. Reference Bentley or online sources but, in general, non-running battery voltage 12-4 - 12.8 Volts is good charge. Running voltage 13.4-14 volts is good alternator output. If alternator output < battery voltage, the battery light will illuminate. If the battery is not being charged, eventually the battery will deplete and the car will not crank. Only replace parts after failure is known. If you don't have Bentley manual, get it.
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mcahn
Posts: 226
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Re: Charging system light

Post by mcahn »

Thanks very much m20power.

The Bentley manual states:

Engine at rest, battery fully charged: 12.6 vdc
Engine running, regulated voltage: 13.2 - 14.5 vdc
Faulty regulator or multi-function controller > 14.8 vdc

I measure:

Engine off: 11.91 vdc
Engine running (AC on): 11.19 vdc
Engine running, (AC, rear defroster, heated seats on): 10.98 vdc
after 5 minutes: 10.29 vdc
after 10 minutes: 8.6 vdc
Turn AC, rear defroster, heated seats off: 9.0 vdc
Engine off: 11.02 vdc

It seems like the alternator might not be working, would you agree? Further diagnosis required? Replace the alternator?

Best,
Matthew

colin
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Re: Charging system light

Post by colin »

At 208,000 miles, my E46 is on its fourth alternator. Failure mode was always the same: constant yellow battery light while driving around. Replacing the alternator always made the problems go away.

With the numbers you're getting, I'd say it's time to replace. Get one from FCP Euro for a lifetime warranty.

On some E46 models, there is an air intake snorkel under the front bumper to direct cooling air to the alternator, and this always gets clogged with leaves and other road debris. I've made cleaning this out part of periodic maintenance.

mcahn
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Re: Charging system light

Post by mcahn »

Thanks, Colin, that's good to know. It sounds like needing to replace the alternator at this mileage is not surprising.

Matthew

warrenbrown
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Joined: Wed Sep 15, 2004 2:24 pm

Re: Charging system light

Post by warrenbrown »

From the numbers you show I agree the alternator is not performing up to par. Like most cars in the last 4 or 5 decades, the E46 alternator has a replaceable voltage regulator. My experience is most likely its the voltage regulator that is bad, it would take more testing to confirm. Unfortunately, most parts sources don't tend to list or stock the regulator separately. To complicate things on an E46 over the life of that model they used 3 different voltage regulator plugs which is on the back of the alternator. Be aware of the plug when ordering a new alternator. On my 2004 330Ci ZHP I had better luck at Advanced Auto. Autozone had the wrong connector, then they wanted to sell me an alternator without a pulley which I was supposed to remove from the original. Don't ask how that is done. My experience may have been just bad luck/good luck.

mcahn
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Re: Charging system light

Post by mcahn »

Thanks, Warren. We actually just picked the car up from the local mechanic. They said that although the car was acting normally, the alternator which is rated at 125 amps was outputting 55 amps. So they replaced the alternator. Last night when we took the car there, my son said everything electrical started going nuts. I noticed looking at the car in my rear view mirror that one headlight was on. Anyway now it seems fine.

I'm hoping I didn't just need a regulator, and it also seemed to me that the rebuilt alternator they sold us was surprisingly expensive. But what's done is done, and that's what I get for not trekking out to Mr. M Car.

On a side note I like that these days every item on the service order starts with "Customer states..." regardless of whether I stated it or not. But it never says anything like "Customer states he brought the car in a couple of weeks ago saying it needed an alternator, and we said no it doesn't, just keep an eye on it, and now we say it needs an alternator, so customer says ok, put in an alternator."

warrenbrown
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Re: Charging system light

Post by warrenbrown »

I suspect you needed a full alternator due to a deeper issue than the VR. I can't explain the weird electrical issues except that I've witnessed similar results after the battery was disconnected. Typically disconnecting the battery has no effect. You can imagine power cycling the battery could create a number of voltage spikes that could disrupt numerous CPUs in their power up cycles. In the case, I witnessed none of the issues have reoccurred.

mcahn
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Re: Charging system light

Post by mcahn »

Yeah, I can imagine if the voltage were low that various parts of the electrical system would behave oddly. One time I had several electrical things not working at once in my E46 M3, a window and I forget what else. Don Fields explained to me that the window switch tells the computer to put the window up or down, and then the computer does it, so if there are three bad things I most likely would need a computer. But after diagnosis it turned out to be three bad switches. I'm not sure why low voltage would turn on one headlight.

Anyway, comforting to know that replacing the alternator was a reasonable thing to do.

RAYADAM
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Re: Charging system light

Post by RAYADAM »

Had a few minutes to read all of this, obviously agree with all the experts above . Just as quick precautionary measure is to check the ground cable connecting the engine to the chassis. make sure it's not corroded (generally see it turning green on exposed cable surfaces). Although cable completely broken would cause starting issues , but a weak cable can cause voltage surges. of course check ground cable from battery to body as well as a piece of mind.
Ray
2011 X5d
2018 Shelby GT350

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