Charging Light On - Alternator putting out 14.1V

[jnclem]

OK brain-trust. What's up with this. My charge light came on the other day. I took the car home, and since is was snowing, didn't do any diagnostics, just put a charger on to top up the battery.

Went out the next morning and started the car. No charge light (went out immediately and stayed out) and alternator putting out 14.1V at the charging port under the hood.

Today, got about 4 miles from the house and the light blinks a few times, then stays on. When I got back home, the light is on, but again, 14.1V at the charging port.

Battery is only a couple of months old, replaced a 6 year old battery that started to fail in cold weather.

Alternator is 3 years old, Bosch, about 40K miles on it.

The only thing I still will be interested to see, is whether after the car cools off completely, the charge light goes out again, then comes on as the car warms up. To me that would indicate a diode board or some such, but I don't really know much beyond what I'm telling you.Right now it is putting out 14.1 at idle.

Thoughts?

[Bdc101]

My charging light started coming on intermittently anf then eventually stayed on, but it would still blink off when I got the revs up past 5,000. I replaced the alt and the light went away. I'm by no means an expert BMW troubleshooter, but this was my experience.

[Clavurion]

Could be nearly worn out brushes. Check the voltage while driving from cluster hidden menu. Still a bit strange if the light was still on when you measured normal charging voltage in engine bay.

[jnclem]

Originally Posted by Clavurion

Could be nearly worn out brushes. Check the voltage while driving from cluster hidden menu. Still a bit strange if the light was still on when you measured normal charging voltage in engine bay.

Right. And if Bosch brushes wear out that fast, I won't be buying another Bosch alternator.

[Clavurion]

Originally Posted by jnclem

Right. And if Bosch brushes wear out that fast, I won't be buying another Bosch alternator.

Ah, just reading your first post again. Not likely just after 40k miles.

[Clavurion]

Not exactly sure if the battery warning light on these works like a comparator circuit. The warning lamp gets other line from battery via fuse. The other line comes from the alternator. So when alternator is not producing that line will work as a ground to that warning lamp and it illuminates if ignition is on. When alternator produces enough voltage it balances the potential difference between line from battery and line from alternator, so there's no current thru the warning lamp and it goes off.

https://www.newtis.info/tisv2/a/en/e...rnator/ooquPcn

[wpoll]

Originally Posted by Clavurion

Not exactly sure if the battery warning light on these works like a comparator circuit. The warning lamp gets other line from battery via fuse. The other line comes from the alternator. So when alternator is not producing that line will work as a ground to that warning lamp and it illuminates if ignition is on. When alternator produces enough voltage it balances the potential difference between line from battery and line from alternator, so there's no current thru the warning lamp and it goes off.

https://www.newtis.info/tisv2/a/en/e...rnator/ooquPcn

Yeah, this looks more complex than the usual charge indicator.

The only way the charge lamp (battery symbol) can normally light is if the DME takes pin 1 on X60004 low, and it'll do this under some sort of logic control, I guess. Could be a dicky DME or a short to ground on that output pin...

Or maybe the alternator connection to the DME is faulty - either pin 2 on X6524 (on the back of the alternator) or pin 13 on X60003 (DME).

4.6iS (M62B46) doesn't have the IVM, does it... only the N62 V8 (N64B44 and N62B48)?

[80stech]

You can't assume the alternator is good by just checking voltage. I would say, take it somewhere to have the charging checked properly including amperage and ripple and go from there.

[jnclem]

Originally Posted by 80stech

You can't assume the alternator is good by just checking voltage. I would say, take it somewhere to have the charging checked properly including amperage and ripple and go from there.

I was thinking that my next step is probably to have it checked by someone with better equipment than I have. I’ve never heard of a battery light on where the alternator was still putting out it’s normal voltage. Generally that is the simple and obvious test, but of course, this is a BMW, so who knows. Seems to always be something a little odd.

[bradb]

Does the light ever blink? If so, I'm probably stumbling down the wrong road, but to just throw it out there that a blinking battery light could be a bad ignition switch.

Brad