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E90/E91/E92/E93 (2006 - 2013)
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  #1  
Old 03-06-2013, 09:16 AM
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raleedy raleedy is offline
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Bad Alternator?

My car is in for a battery replacement after the original battery was showing some signs of giving out (slow cranking in cold weather, and in one instance the starter draw coincided with the clock, BC and trip mileage zeroing out). That all seems pretty straightforward. But the dealer wants to replace the alternator, too, claiming that is it putting out >15 volts instead of the expected 14.5. This is pricey. (~$1K.) In searching I can't find a single instance on this board of alternator problems. Should I get a second opinion?
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  #2  
Old 03-06-2013, 09:19 AM
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CALWATERBOY CALWATERBOY is offline
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Quote:
Originally Posted by raleedy View Post
My car is in for a battery replacement after the original battery was showing some signs of giving out (slow cranking in cold weather, and in one instance the starter draw coincided with the clock, BC and trip mileage zeroing out). That all seems pretty straightforward. But the dealer wants to replace the alternator, too, claiming that is it putting out >15 volts instead of the expected 14.5. This is pricey. (~$1K.) In searching I can't find a single instance on this board of alternator problems. Should I get a second opinion?

Yup.

How do they say it's failing, exactly?
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  #3  
Old 03-06-2013, 09:25 AM
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DSXMachina DSXMachina is offline
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Quote:
Originally Posted by raleedy View Post
My car is in for a battery replacement after the original battery was showing some signs of giving out (slow cranking in cold weather, and in one instance the starter draw coincided with the clock, BC and trip mileage zeroing out). That all seems pretty straightforward. But the dealer wants to replace the alternator, too, claiming that is it putting out >15 volts instead of the expected 14.5. This is pricey. (~$1K.) In searching I can't find a single instance on this board of alternator problems. Should I get a second opinion?
There have been a lot of battery threads recently and I don't remember whether you were one who said their alternators were charging in the upper 14's or not. That would be normal. Unlikely it suddenly went bad if so. If it were my car I'd drive it home like it is as long as you're not going too far. Then I'd check it myself when I got home.
Your alternator is charging excessively if they are correct. As I mentioned in another thread, there is always the possibility that overcharging cooked the battery and that's why the poster's battery was bad. This could have happened to you, i.e. a bad alternator ruined the battery. On the other hand, it you want to be certain, get the car back, do a short trip and check it yourself.
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  #4  
Old 03-06-2013, 11:26 AM
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raleedy raleedy is offline
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Originally Posted by CALWATERBOY View Post
Yup.

How do they say it's failing, exactly?
Through too much success -- higher than normal voltage output. It could have damaged the battery, although mine is the factory original dating from 10/07, so it is sort of on borrowed time. All the talk about the need for battery registration, because that is how the IBS knows how to limit charging and protect against overcharging, has just set my weak little head to spinning. Apparently there's a distinction between excess voltage and overcharging. So the overcharging is going to be applied to my Visa card.
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  #5  
Old 03-06-2013, 11:34 AM
RBinDC RBinDC is offline
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Quote:
Originally Posted by raleedy View Post
My car is in for a battery replacement after the original battery was showing some signs of giving out (slow cranking in cold weather, and in one instance the starter draw coincided with the clock, BC and trip mileage zeroing out). That all seems pretty straightforward. But the dealer wants to replace the alternator, too, claiming that is it putting out >15 volts instead of the expected 14.5. This is pricey. (~$1K.) In searching I can't find a single instance on this board of alternator problems. Should I get a second opinion?
Why would the alternator have to be replaced? there has to be a regulating device which determines the voltage output of the alternator. Typically this is done by setting the excitation current that magnetizes the rotor. While I have no idea how BMW alternators are designed to work it is hard to believe that the output voltage can't be adjusted.
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Old 03-06-2013, 11:47 AM
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raleedy raleedy is offline
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Originally Posted by RBinDC View Post
Why would the alternator have to be replaced? there has to be a regulating device which determines the voltage output of the alternator. Typically this is done by setting the excitation current that magnetizes the rotor. While I have no idea how BMW alternators are designed to work it is hard to believe that the output voltage can't be adjusted.
And yet that seems to be how it is, also according to experience reported by others.
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  #7  
Old 03-06-2013, 12:04 PM
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DSXMachina DSXMachina is offline
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The BMW alternator is internally regulated, but it is "excited" by a 12V signal from the PCM rather than direct from the battery. That's why the PCM need to be advised when the battery is changed, so that the PCM controls charge rate appropriately.
Can the regulator be changed without changing the alternator? On most cars yes, but I don't know if they are available for a BMW alternator. We always change the entire alternator so as not to get bit later by a bad alternator winding, brush or bearing. That, of course, would always end up with the customer saying "You guys just fixed my alternator and now it's doing the same thing!"
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Old 03-06-2013, 03:10 PM
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I looked on Realoem and found the voltage regulator offered separately from the remanufactured alternator, but that wasn't what was recommended to me, so I got the whole package. I'm guessing the labor involved would be about the same either way, but the part price difference is substantial.

Last edited by raleedy; 03-06-2013 at 03:11 PM.
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  #9  
Old 03-06-2013, 03:10 PM
RBinDC RBinDC is offline
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Originally Posted by DSXMachina View Post
The BMW alternator is internally regulated, but it is "excited" by a 12V signal from the PCM rather than direct from the battery. That's why the PCM need to be advised when the battery is changed, so that the PCM controls charge rate appropriately.
Can the regulator be changed without changing the alternator? On most cars yes, but I don't know if they are available for a BMW alternator. We always change the entire alternator so as not to get bit later by a bad alternator winding, brush or bearing. That, of course, would always end up with the customer saying "You guys just fixed my alternator and now it's doing the same thing!"
Ah, DSX,

I thought you would know the answer.
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  #10  
Old 03-06-2013, 03:33 PM
Woody Woody is offline
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Shouldn't the red battery light be coming on?
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  #11  
Old 03-06-2013, 06:33 PM
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Shouldn't the red battery light be coming on?
I could probably have waited for that, but I had other symptoms earlier.
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  #12  
Old 03-06-2013, 08:59 PM
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I could probably have waited for that, but I had other symptoms earlier.
The red light comes on only to warn you of UNDER charging. It doesn't come on for overcharging.
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  #13  
Old 03-07-2013, 12:04 AM
BashedBarrique BashedBarrique is offline
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Quote:
Originally Posted by DSXMachina View Post
The BMW alternator is internally regulated, but it is "excited" by a 12V signal from the PCM rather than direct from the battery. That's why the PCM need to be advised when the battery is changed, so that the PCM controls charge rate appropriately.
Can the regulator be changed without changing the alternator? On most cars yes, but I don't know if they are available for a BMW alternator. We always change the entire alternator so as not to get bit later by a bad alternator winding, brush or bearing. That, of course, would always end up with the customer saying "You guys just fixed my alternator and now it's doing the same thing!"
I have replaced internal regulators, brushes and bearings but have never had a "winding" failure. How do the windings fail? Short caused by foreign object intrusion? Insulation failure?
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  #14  
Old 03-07-2013, 05:07 AM
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Originally Posted by BashedBarrique View Post
I have replaced internal regulators, brushes and bearings but have never had a "winding" failure. How do the windings fail? Short caused by foreign object intrusion? Insulation failure?
It's rare due to the quality of the insulating varnish used nowadays but it still happens. Just like coil failure in ignition coils and injectors, who knows why they break down the way they do? Higher underhood and component temperatures, high frequency vibration, salt invasion, weak construction? All guesses on my part.
(Good to meet someone else who has actually rebuilt an alternator. I threw out my starter growler a long time ago and never open those anymore. Never open compressor cases except to learn, and can't recall the last CV joint I disassembled and rebuilt. The last carb I rebuilt was a few years ago. Times change eh?)
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  #15  
Old 03-07-2013, 11:53 AM
BashedBarrique BashedBarrique is offline
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Originally Posted by DSXMachina View Post
(Good to meet someone else who has actually rebuilt an alternator. I threw out my starter growler a long time ago and never open those anymore. Never open compressor cases except to learn, and can't recall the last CV joint I disassembled and rebuilt. The last carb I rebuilt was a few years ago. Times change eh?)
Yeah, with the availability of inexpensive rebuilt units on most parts it hardly makes sense to rebuild things anymore. It is fun to open them up to see how they work even if you're just pitching it later.

I haven't rebuilt a carburetor in probably twenty years. I saw a radiator shop in my area the other day and I wondered how they stay in business. You can buy inexpensive new radiators for around $100.
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Old 03-07-2013, 12:29 PM
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Originally Posted by BashedBarrique View Post
Yeah, with the availability of inexpensive rebuilt units on most parts it hardly makes sense to rebuild things anymore. It is fun to open them up to see how they work even if you're just pitching it later.

I haven't rebuilt a carburetor in probably twenty years. I saw a radiator shop in my area the other day and I wondered how they stay in business. You can buy inexpensive new radiators for around $100.
If they've kept up with the times they've had to change. Nowadays there's no money in car radiator repair for the reason you mentioned, and not as much as there once was in heavy duty repair. However, real heavy duty (mining and oil drilling rigs, compressor and standby generator radiators, marine heat exchangers, locomotive and land clearing) is still capable of supporting a good living if you're lucky enough to live in an area which can supply you. Otherwise your shop will have had to shift from soldering to MIG/TIG welding of intercoolers, charge air coolers and similar, and repair of industrial oil to air or water heat exchangers. There's still money to be made but you have to be a lot smarter and more flexible to make it.
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  #17  
Old 03-08-2013, 11:35 AM
BashedBarrique BashedBarrique is offline
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There's still money to be made but you have to be a lot smarter and more flexible to make it.
Yeah, I guess like any smart entrepreneur you have to adapt to the market and market your skills accordingly.
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Old 03-08-2013, 02:26 PM
Pilgrim Pilgrim is offline
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How about a definition of two acronyms: IBS and PCM?

Trying to keep up, but those are not clear to me.
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  #19  
Old 03-08-2013, 04:12 PM
Tom K. Tom K. is offline
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How about a definition of two acronyms: IBS and PCM?

Trying to keep up, but those are not clear to me.
Can't help with PCM, but IBS stands for Internal Battery Sensor. It resides in the BMW's negative battery cable and controls the rate of charge. The primary reason for battery registration is so that the IBS will play nice with the alternator and the battery wil be properly charged.

Tom
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Old 03-08-2013, 05:00 PM
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GarySL GarySL is offline
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PCM= Powertrain control module or ECU
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Old 03-08-2013, 05:01 PM
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raleedy raleedy is offline
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I believe PCM refers to one of the control modules, most likely the Powertrain Control Module.
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Old 03-08-2013, 08:19 PM
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DSXMachina DSXMachina is offline
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Originally Posted by Tom K. View Post
Can't help with PCM, but IBS stands for Internal Battery Sensor. It resides in the BMW's negative battery cable and controls the rate of charge. The primary reason for battery registration is so that the IBS will play nice with the alternator and the battery wil be properly charged.

Tom
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PCM= Powertrain control module or ECU
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Originally Posted by raleedy View Post
I believe PCM refers to one of the control modules, most likely the Powertrain Control Module.
Right, PCM is the universal name assigned by the Society of Automotive Engineers to the main computer in charge of the engine and transmission, the Powertrain Control Module. The SAE came up with all the acronyms way back in the early days of OBD2, on board diagnostics. They're also the same people who assigned all the 'P' codes which all PCMs use to identify emissions related faults.
All OEMs are required to make all emission fault codes readable by the aftermarket, and everyone's P codes mean the same thing. Example, a P0301 code means that cylinder #1 is misfiring no matter who made the car.
Every OEM must refer to all emission related component by exactly the same name, so an air fuel ratio sensor, a mass air flow sensor, a barometric pressure sensor, etc. are all called the same thing by everyone.
If that's so, then how come you often hear BMW call the PCM by another name? Simple, they can call it anything they want internally, but when they publish data to the trade they have to use standardized terminology. If they don't, the EPA (not the SAE) will send them a friendly reminder.
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  #23  
Old 03-08-2013, 08:39 PM
Pilgrim Pilgrim is offline
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Thanks, gents. I was familiar with ECU as a term, but not PCM. THe IBS info is helpful, too. Muchas gracias.
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  #24  
Old 03-09-2013, 01:38 AM
BashedBarrique BashedBarrique is offline
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I hate it when people use acronyms (or more often abbreviations) for which they don't know the full name.

My ex-wife worked for GTE and when she came home from her new employee orientation I asked her what GTE stood for. She said that never came up. She had a big folder full of company information they had given her. I looked through it and there was no mention of what GTE stood for. There was an 800 number "Information Line" so I called it. I asked the person that answered what GTE stood for.

She said "It doesn't stand for anything, it's just the name of the company."

I said "It must have stood for something at some time. Maybe General Telephone and Electric or General Telegraph and Electronics or something?"

She said "Perhaps, but I don't know what that was."

She transferred me to no less than eight different executives that weren't any more sure than me! Finally one guy, some VP of Engineering or something said,

"It was originally General Telephone Corporation and then they merged or absorbed a couple of electronics companies (Sylvania being one of them) and became General Telephone and Electronics (GT&E). And then in 1982 they dropped the "&" and just went by the name GTE (just the three disembodied letters)"

I couldn't believe that there were tens of thousands of employees of this company and most of them didn't know what the name stood for, or apparently care.
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  #25  
Old 03-09-2013, 09:36 AM
steverequiem steverequiem is offline
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Had to replace my alternator, but only after the red battery light came on.
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