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DIY: Do It Yourself
Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

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Old 08-19-2010, 05:03 PM   #1
snorcup
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Join Date: Jun 2008
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Troubleshooting: alternator or Voltage Regulator

Hey guys, thanks for all the help along the way.

I don't post much but I read constantly.

A few months ago I put a new battery in my car since it was doing some quirky things, and most importantly, not starting.

The replacement battery fixed my problems, but I have been noticing for the past week or so the power windows are a bit slow, and when cranking the starter seems a bit sluggish.

Today when driving home and playing the radio at a loud volume, I got some intermittent flashes of the red battery light, so since the battery is new I'm assuming the alternator is going.

I started reading here and it seems like people have good results replacing the voltage regulator assembly, but since my car is my only way back and forth to work, I don't want to order a voltage regulator and be out of service an extra 2-3 days waiting on an alternator if that isn't the culprit. On the other hand, I would prefer to save a couple hundred dollars if it's just the regulator.

Whats the best way to diagnose a failed voltage regulator vs. a failed alternator?

If this is covered in another post then I apologize in advance, but most of what I have seen appears to more of a "try the regulator first" approach as opposed to a "verify it's the regulator by" method, which is what I'm more comfortable with.

Thanks!

Steve
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Old 08-20-2010, 11:16 AM   #2
hummer
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How many miles on the car? Replacing the regulator can be a crap shoot! I would first remove the belt and check the integrity of the bearings. If the shaft wobbles or the bearings are not smooth and turning freely, I would replace the alternator with a Bosch 120 amp remanufactured unit at approx $200.
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Old 08-20-2010, 11:45 AM   #3
snorcup
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Guess I should have included that...

Its a 2001 330ci with 110,000

Sent from my DROIDX using BimmerApp
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Old 08-20-2010, 01:47 PM   #4
Arty
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Get a voltmeter for 5 and measure accross the battery terminals with the engine running. Expect 13-14V.
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Old 08-24-2010, 05:41 PM   #5
snorcup
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Arty,

Thanks for the reply, but it doesn't accomplish anything. Putting a multimeter at the battery terminals will only determine if there is enough voltage or not. If there wasn't, the alternator or the VR could still be the culprit, and the entire point of the post was trying to narrow down which one of those two it was.

Anyways, I decided to go and get a replacement alternator since I didn't have time to "try" the VR first.

I found a rebuilt Bosch 120 amp alternator at CarQuest for $229.00.

The DIY was not too tough, but I wanted to share a few tips....

Pulling the air box was not too tough, and took a 10mm socket and flat head screw driver

My car is a 2001 330Ci 5 speed. The fan was electric, the alternator again was the Bosch 120 amp, and it did have a bolt on the bottom and the top.

I started by taking the belt off. Make sure you make a map of the belt before you take it off! The tension pulley takes a T-50 torx bit. People say they had trouble with this, but I had no problem getting it to move with the right bit and a standard ratchet. I found it easy to move the tension pulley then pull the belt off the alternator pulley, since it was on top and easy to get to with the air box out.

Although it was tight, I was able to do this without removing the fan. From what I have read mechanical fans need to come out.

The top alternator bolt also had pulley on it. This confused me for a few minutes. The bolt took a 16 or 17mm socket, and I didn't need an extension for this one.

Once the top bolt and pulley was out, the bottom one was under the alternator. If you put your hand on the front of the alternator, go to the bottom and it is about dead center. I used a deep socket for this one, and a short extension. This bolt was a little tough with the fan in place, but manageable.

There is a wiring harness on the back of the alternator that needs to come out, and a power lead, which if I remember used a 15mm socket. It's a big plastic covered nut.

There's also a piece of duct work that attaches to the plastic shroud on the back of the alternator. There was no fastener on this, it simply pulled off.

That's it, the old one is out.

Going back in, the bottom of the alternator has two "wings". The bolt passes through the front and threads in the back, and these sit on either side of a flange on the block. On my car, the "wings" were tight on the flange. What I did was get the top lined up and put the top bolt in loose, and then used a mallet to seat the bottom portion onto the flange. Also I was using my cell phone camera to get pictures of the bottom to see when it was lined up, since I had no other way to get my eyes on it.

Did you make a map of the belt before you took it off? If not, go google a diagram now, which is what I had to do, although now that I'm writing this I can't find it. Also, when putting the belt back in people say to seat it on everything, then put it on the tension pulley last. This seemed stupid since it's hard to manipulate the tension pulley with the belt in the way. Much like when I took it off, I left it off the alternator since it's easy to get to, pulled on the tension pulley, and then seated it back on the alternator. Make sure you have the belt seated in the grooves of the pulleys.

Everything else was the reverse of taking it out.

Sorry, no pictures was in a rush. Even so it took me roughly 3 hours, not including running to the car quest on the other end of the city in rush hour.

Good luck

Last edited by snorcup; 08-24-2010 at 05:46 PM.
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Old 08-24-2010, 05:58 PM   #6
jcns
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a multimeter would have helped.
based on your original post, it SOUNDS like the voltage regulator.
Signs of a Bad Voltage Regulator include car lights go dim, the lights on the panel and the radio also dim, the battery light on the panel shows either a high charge or a low charge. You may also notice a sulphur-like smell.
By using the voltmeter, with the car running, you can measure the voltage at the battery terminals. If you got consistently ~14v, the alternator is in good working condition, which eliminates it from the equation.
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Old 08-26-2010, 04:10 PM   #7
havnfun328
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I pulled my alternator when I replaced my oil filter housing gasket. Two comments:

1) Be sure to disconnect the battery before you take the main lead off the alternator.
2) For manual transmissions pulling the electric fan is very easy and well worth the effort to give more space to work.

My $0.02.
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Old 09-24-2010, 12:13 PM   #8
flyboy737
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Hi Guys,
I did the voltage regulator on my 2001 BMW 330i yesterday. Total cost for a brand new voltage regulator on a Bosch A120 alternator was less than $45. R300 in South Africa from Diesel Electric the Bosch importers.
I had NO battery light or other indications of the failure. The battery voltage however remained low during normal operation. After the car had warmed to normal temp the charging voltage over the terminals of the battery was 13,2v This is around 1.2 volt too low. You need 14.2 - 14.5 volt to keep a 12v battery fully charged. I had to charge the battery once a week to keep the car running. The battery was tested by a battery expert and found to be perfect, but not charged. (70% charged at test).

Under-voltage is even more dangerous to electronics than water! So I replaced the voltage regulator ASAP. My car has only covered 50 000Km and the alternator bearings are quiet, so no need for an alternator replacement.

The regulator uses 13 diodes to rectify / regulate the current. A failure of a single diode will / did result in a voltage drop of 1.12volt.

New regulator fitted, and the alternator is charging at 14.2v with headlights on bright & cabin fan at max speed.

My pride and joy restored to it's full glory!
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Old 10-08-2010, 03:29 PM   #9
sistylez
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Hey I am thinking about doing this next week during fall break for my girl's car. She has a 2001 325Ci. The bmw service shop measured 13v with the multimeter and told her that she would need a new alternator. They quoted her 400 for the part and 100 for the labor.

Thanks to E46 Fanatics, I know that this price was a bunch of crap and did my research.

Her car has approximately 130,000ish miles on it. It has been nothing but hell for me because I do a lot of the maintenance whenever something happens with it for the sake of saving her money.

Should I just buy the new alternator and replace the entire unit? How do I know if it is the alternator or the voltage regulator that is failing? Because if it is just the regulator, that would be a price difference of $200 dollars. I have looked at a couple of the alternator DIY removals on this site and it seems simple enough.
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Old 01-25-2011, 11:14 PM   #10
FFWD
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I have a 1999 323i with 300,000 kms (188,000 miles). Voltage shows 10.99 using the charging posts in the engine bay when the car is idling, and doesn't change when the engine is revved up past 2000 RPM (I remember it increasing two months ago when I was diagnosing my starting problem, so at the time the alternator was good). It shows 12.0 when the car is off. The alternator is not making any noises, so does this mean I can get away with just changing the voltage regulator? Would like to save a few bucks here if I can - I just spent $1500 in the last two months on a new starter, hood latches and cables, and climate control blower motor. Thanks!
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Old 02-02-2011, 08:54 AM   #11
druggrepp
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I also had batt lite come on intermittently. 187k so it was time for wierd stuff.
First attempt to fix, cleaned terminals w wire brush and charged batt overnite. Voltmeter showed 14.5 volts at batt. No batt or abs lite after that. When i changed belts and pulleys i spun original alt and bearings were noisy.
A month later it started again so i got another alt and had to replace intake boots and clean icv anyway cause of wierd idle so it was easy to get old alt out.
I wanted to see how easy it is to change regulator... It is a snap. Cover comes off alt w 3 screws and reg comes off w 3 screws.
Putting it back on requires making a small stiff wire to hold brushes back in so you can slide it down over amrature.
New alt on, cleaned terminals again and charged batt. Took 500 mile trip and all is good.
Bottom line, if you alt bearings aren't shot , try a regulator, pelicanparts.com.
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Old 02-13-2011, 02:31 PM   #12
denpmp
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I just replaced the VR on my ride, it's tight in there but doable without removing the alt. Did you have any starting isseus after replacing yours? I've charged up the bat and my starter is cranking but the engine doesn't turn over? I'm wondering if in the process I managed to disconnect a plug/wire or something that is now messing things up? In the process I found one main power line connected to the VR by the large plastic headed nut mentioned earlier; one plug to the VR; and one plug to the air supply monitor, all reconnected in reverse order? Did you have to deal with anything else? Thanks.
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Old 07-04-2013, 11:27 PM   #13
iPnoy
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only 2 things to find out

first 1.)check that voltage regulator's condition and 2.)have a look for signs of terminal live feedbacks from AC to V.R, if there is no problem with grounding between those connections if you have the basic tester(big deal) Otherwise it has to be the alternator, and if you ever to consider a pocket saving possibility double check that VR first or bring that to somewhere theyre able to test it free of charge like auto parts store of friend you might have in mechanic shops who likes coffee lol., if thats the case then you just saved some bucks!
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Old 09-30-2013, 05:56 PM   #14
dankjono
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Quote:
Originally Posted by flyboy737 View Post
Hi Guys,
I did the voltage regulator on my 2001 BMW 330i yesterday. Total cost for a brand new voltage regulator on a Bosch A120 alternator was less than $45. R300 in South Africa from Diesel Electric the Bosch importers.
I had NO battery light or other indications of the failure. The battery voltage however remained low during normal operation. After the car had warmed to normal temp the charging voltage over the terminals of the battery was 13,2v This is around 1.2 volt too low. You need 14.2 - 14.5 volt to keep a 12v battery fully charged. I had to charge the battery once a week to keep the car running. The battery was tested by a battery expert and found to be perfect, but not charged. (70% charged at test).

Under-voltage is even more dangerous to electronics than water! So I replaced the voltage regulator ASAP. My car has only covered 50 000Km and the alternator bearings are quiet, so no need for an alternator replacement.

The regulator uses 13 diodes to rectify / regulate the current. A failure of a single diode will / did result in a voltage drop of 1.12volt.

New regulator fitted, and the alternator is charging at 14.2v with headlights on bright & cabin fan at max speed.

My pride and joy restored to it's full glory!
My e46 has had the same issues. I replaced the voltage regulator but it still says charging at 13.1v -13.3v. Any thoughts?
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Old 10-01-2013, 10:44 PM   #15
andynicks
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Dankjono - I took a chance and replaced the voltage regulator on my '04 325xiT about an hour ago instead of replacing the entire Valeo alternator. I should have bought the alternator. The battery light is still on and using the OBC (http://forums.bimmerforums.com/forum...46-Easter-Eggs), found my battery only has 11.6V across and doesn't increase with RPM. Seems the alternator itself is bad. The $ difference was only $120 or so and would have saved me from doing it all over again. Ahh well, co-worker will have to pick me up for another couple days...
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Old 10-01-2013, 10:54 PM   #16
dankjono
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Quote:
Originally Posted by andynicks View Post
Dankjono - I took a chance and replaced the voltage regulator on my '04 325xiT about an hour ago instead of replacing the entire Valeo alternator. I should have bought the alternator. The battery light is still on and using the OBC (http://forums.bimmerforums.com/forum...46-Easter-Eggs), found my battery only has 11.6V across and doesn't increase with RPM. Seems the alternator itself is bad. The $ difference was only $120 or so and would have saved me from doing it all over again. Ahh well, co-worker will have to pick me up for another couple days...
It ended up being the positive cable running from the engine bay to the battery. You should check the voltage on the positive jumper terminal in the engine bay and see if it pumping out 14+v.

http://forum.e46fanatics.com/showthr...2&goto=newpost
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Old 10-01-2013, 11:06 PM   #17
dankjono
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If you installed halos on your car it's most likely shorting out at the 12v terminal. I'd check the connections for corrosion and melted soder and plastic. You need to pry of a plastic piece that's connected to the hood alarm sensor. Once that is out you should be able to see the wire
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