battery warning light, low headlight output, then trans failsafe = alternator?

John Galt · #1 02-28-2019, 11:37 PM

Is this problem likely the alternator?

Is it best to replace the whole thing, or can I just replace the regulator? In other words, is it common for just the regulator to fail, or is it normally something else in the alternator?

E53 3.0i

So, I'm driving home from work today and the battery warning light was on the dash.

Then I noticed that the headlights seemed a bit dim.

Then I got a bunch of other warning lights.

Then the trans fail safe came on.

I managed to get home, but the car would not turn over after I turned it off. Dead battery symptoms when I tried to start it again.

The battery is maybe one year old.

I have not had any recent electrical or starting related issues.

The car has 200k miles.

I'll try to jump start it and check out the running voltage tomorrow.

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EODguy · #2 03-01-2019, 02:18 AM

After everything you listed the only reason to charge it is so you can drive to get a new alternator. I'm not saying that the regulator shouldn't be tried but sometimes it works out cheaper in it time and stress to just go for it right away.

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cslee · #3 03-01-2019, 02:37 AM

The same thing happened to me last week. I change the alternator. All fine now.

EODguy · #4 03-01-2019, 02:49 AM

Yeah I just changed my alternator but that's cause mine had 208,000 km on it and it cracked the housing next to the pulley

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andrewwynn · #5 03-01-2019, 08:43 AM

I refurbished mine with a kit including new brushes and slip rings. $20 and about an hour of my time. I have valeo air cooled. Not sure which models have the kit but I was very happy mine had the kit. It wasn't very difficult to install.

CleanIsFast · #6 03-01-2019, 11:29 AM

Similar symptoms and changed alternator and no issues anymore.

Fifty150hs · #7 03-01-2019, 11:54 AM

Quote:

Originally Posted by John Galt

Is this problem likely the alternator?

Is it best to replace the whole thing, or can I just replace the regulator? In other words, is it common for just the regulator to fail, or is it normally something else in the alternator?

E53 3.0i

So, I'm driving home from work today and the battery warning light was on the dash.

Then I noticed that the headlights seemed a bit dim.

Then I got a bunch of other warning lights.

Then the trans fail safe came on.

I managed to get home, but the car would not turn over after I turned it off. Dead battery symptoms when I tried to start it again.

The battery is maybe one year old.

I have not had any recent electrical or starting related issues.

The car has 200k miles.

I'll try to jump start it and check out the running voltage tomorrow.

Classic bad alternator symptoms.

oldskewel · #8 03-01-2019, 01:06 PM

Yes, those symptoms exactly fit an alternator failure. Charging the battery will be good to do, both so you can drive the car a few miles (<10) and so the "new" alternator does not have to charge up a dead battery.

In my experience, including with my 2001 3.0i, the brushes are the first failure point. In these cars they come either with a Bosch or a Valeo alternator, and the only way to really tell is by looking at the label on what you've got in there (for me, realoem with my VIN was wrong).

If replacing the whole alternator (including pulley), they are interchangeable. But the voltage regulators are not interchangeable between Bosch/Valeo, nor are the pulleys.

At least on the Valeo (and I assume on the Bosch too), the brushes are part of the voltage regulator assembly. Replacing the VR and a light cleaning of the slip rings will likely solve your problem. Replacing the VR is about 1/10 the effort and skill level of R+R'ing the alternator.

As AndrewWynn said, and as I have done too, you can replace just the brushes.

Or you can replace the whole alternator. Or you can buy a new car. Any of the above should get you back on the road.

andrewwynn · #9 03-02-2019, 02:29 AM

https://www.icloud.com/sharedalbum/#B0SJsHvHoGjXxga

My photos from fixing my alternator

I discovered that only one slip ring has any significant wear and I'm hoping I can take my wife's out and reverse the polarity to the field winding to basically double the lifespan of the alternator.

Cutting the copper bars that supply the current and soldering on some crossover jumpers should do the trick. It will save an hour or two of time not needing to even take the end off the alternator, just tweak the VR.

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