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      10-08-2017, 03:10 AM   #1
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Voltage drop to 11.9v randomly

Hey all, so I've been having bsd lines codes come up randomly so recently while.monitoring my car, my voltage while running usually stays around 13.9 but sitting at idle I saw it drop to 11.9. I revved it up and it went to 12.2. turned off the car and restarted and it was back to 13.9. At this point I noticed all the bsd line codes come on the ecu.

I'll check my ground strap tomorrow and maybe add a second wire for ground but do y'all think this is bad alternator? Should I change the whole alternator or just the regulator?


update 10-30-17: changed alternator. still got a drop after alot of stop and go in traffic. accelerated and shifted at 5k. voltage went from 14 slowly to 11.9/11.8.

Update 11-06-17: have disconnected the 2 blue cables the IBS on the negative batt cable for a few days now and so far bat voltage is at 14.1v instead of 13.9v as usual and i have not encountered any dips in voltage to under 12v or spikes to 18v. seems like IBS was randomly telling the ecu to reduce or increase voltage. i have codes on ecu for disconnected IBS but no CEL so all good. will report back if this is a fail! ha

Update 11-17-17: voltage shot up to 18v again. All bsd Missing codes again. Was sitting in drive thru on a hot day and floored it when I was trying to get thru traffic. Tsc kicked in the voltage shot to 18v. Restarted car and back to 14v. Maybe ecu getting too hot?



attached a log when it occured on few days ago.


https://datazap.me/u/racermp/e90-n55...=3-4&zoom=0-59


On my 2011 e90 n55
Thanks all
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      10-09-2017, 02:25 PM   #2
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Quote:
Originally Posted by racermp View Post
Hey all, so I've been having bsd lines codes come up randomly so recently while.monitoring my car, my voltage while running usually stays around 13.9 but sitting at idle I saw it drop to 11.9. I revved it up and it went to 12.2. turned off the car and restarted and it was back to 13.9. At this point I noticed all the bsd line codes come on the ecu.

I'll check my ground strap tomorrow and maybe add a second wire for ground but do y'all think this is bad alternator? Should I change the whole alternator or just the regulator?

On my 2011 e90 n55
Thanks
I just posted this in another thread but the way I was able to diagnose the fact that my ground was bad was by using multiple ground points on my multimeter when testing alternator output. Depending on where you're grounding your multimeter you could be seeing vastly different results. I went as far as to replace my alternator a second time and buying a new battery before realizing my ground strap was the problem.

Using the engine block as your ground and the alternator output for your positive, take your measurements. Then check using the strut bolts as your ground. Then the battery. If your measurements drop you could have a bad ground.

However, I never threw any codes though when I was having these issues. The battery just wasn't charging and would hang from anywhere between 12.1-12.4. Since you're seeing codes I would assume this is not your issue.
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      10-09-2017, 02:29 PM   #3
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Quote:
Originally Posted by nissubaru View Post
I just posted this in another thread but the way I was able to diagnose the fact that my ground was bad was by using multiple ground points on my multimeter when testing alternator output. Depending on where you're grounding your multimeter you could be seeing vastly different results. I went as far as to replace my alternator a second time and buying a new battery before realizing my ground strap was the problem.

Using the engine block as your ground and the alternator output for your positive, take your measurements. Then check using the strut bolts as your ground. Then the battery. If your measurements drop you could have a bad ground.

However, I never threw any codes though when I was having these issues. The battery just wasn't charging and would hang from anywhere between 12.1-12.4. Since you're seeing codes I would assume this is not your issue.
thanks i'l give this a try. i just changed my battery today because it was a year old napa non-agm. went with duralast agm. i looked at the ground yesterday and it looked ok, but hard to tell i it's good. i'll probably replace it anyways because its' not too exp. but i'll try voltage checks and see if it drops. thanks
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      10-11-2017, 02:53 PM   #4
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i purchased a new autozone agm battery and installed it. however while driving on the freeway, i saw the power on the mhd app drop from 13.9 to 12v. reving dind't bring it up. turned off the car, restarted, back to 13.9v.

so i checked the voltage with a voltmeter at the battery while car is off, 12.7. hood terminals, 12.7. engine block to alternator, 12.7
started the car, hood terminals, 14.9.
alternator to engine block, 14.9
alternator to strut bolt and a few different points on the body, 14.9


i added a second ground, like 8-10 guage wire between the charge pipe bracket and powersteering coolant . i didn't see any increase in voltage or decrease. i'll drive around for a few days and see if the voltage drops to 12v.

if restarting brings up the voltage, i wonder if it's something else telling the alternator to drop voltage? i donno
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      10-11-2017, 04:11 PM   #5
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Quote:
Originally Posted by racermp View Post
i purchased a new autozone agm battery and installed it. however while driving on the freeway, i saw the power on the mhd app drop from 13.9 to 12v. reving dind't bring it up. turned off the car, restarted, back to 13.9v.

so i checked the voltage with a voltmeter at the battery while car is off, 12.7. hood terminals, 12.7. engine block to alternator, 12.7
started the car, hood terminals, 14.9.
alternator to engine block, 14.9
alternator to strut bolt and a few different points on the body, 14.9


i added a second ground, like 8-10 guage wire between the charge pipe bracket and powersteering coolant . i didn't see any increase in voltage or decrease. i'll drive around for a few days and see if the voltage drops to 12v.

if restarting brings up the voltage, i wonder if it's something else telling the alternator to drop voltage? i donno
Sounds like a bad alternator to me if changing your ground points didn't make any difference. You could probably mess with the wires back there and make sure they're all connected & tight & don't look discolored or anything. Check the Power Distribution Box on top of the battery for signs of damage too like melting or discoloration.

How many miles on the car?

Also what are the codes you're throwing? If it's saying anything about the IBS then you might just need to replace the negative battery cable (IBS)
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      10-11-2017, 04:20 PM   #6
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Quote:
Originally Posted by nissubaru View Post
Sounds like a bad alternator to me if changing your ground points didn't make any difference. You could probably mess with the wires back there and make sure they're all connected & tight & don't look discolored or anything. Check the Power Distribution Box on top of the battery for signs of damage too like melting or discoloration.

How many miles on the car?

Also what are the codes you're throwing? If it's saying anything about the IBS then you might just need to replace the negative battery cable (IBS)
so when the voltage drops to under 12v, i get the codes in the attachment. but when the voltage stays up around 13.9, i don't have these BSD line codes. oil sensor and everything works, no overheating, nothing.

the only code i constantly get is the 387f - power managment standby violation. thats been there on an off since i bought the car.

on attachment is 14v that i usually see. then the second screenshot is 12v, when it does drop. and the only way i can get it to come back up is to restart the car. maybe this points to the regulator? i haven't seen anything higher than 14s on the mhd app.

oh car has 83k mi

I just changed the battery and looked.at the power box, looks ok, wasn't melted or anything. power at the cables looks ok. such an odd voltage drop that only a restart fixes.it.
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      10-11-2017, 07:59 PM   #7
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ok so I think I may have a break thru.

drove around quite a bit this evening, voltage stayed around 13.9 on mhd app. then in Manual mode, went wot on 3 to 4k and shifted to 4, I say the voltage drop to 12v. kept the car running in a parking lot. measured voltage at alternator, 12.2v. scanned ecu, all bsd line codes errors again.

then I tried that again after a reset, this time shifting 3-4 around 4krpm I got 18v. wipers, all lights and everything came on. stopped the car, restarted and back to 14v.

tried to log mhd and try again, couldn't catch it 3-4 times. but when not logging, I think happened again on 2nd wot, back to 12v.

maybe when the engine jolts back and forth something is causing the issue or I donno why.

voltage regulator ?
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      10-11-2017, 08:04 PM   #8
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Hmm. Can't say exactly. You are getting an IBS message which is interesting. I don't recall having any codes like yours but then again my problem may never have been the alternator in the first place. I had a bad ground strap as I mentioned but replaced the alternator in the process.

If it were me I'd really look into the IBS, then the alternator.

https://www.bimmerscan.com/bmw-intel...ry-sensor-ibs/

https://www.newtis.info/tisv2/a/en/e...ttery/1LyvW9MF

"...only exchange the IBS when there is a corresponding fault code entry!"

BMW is pretty clear on not replacing the IBS unless its actually the problem. They say in one of those articles that they've tested "defective" devices that were replaced and they were fine. Unfortunately I'm not sure how to determine whether its defective or not.
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      10-11-2017, 08:05 PM   #9
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Quote:
Originally Posted by nissubaru
Hmm. Can't say exactly. You are getting an IBS message which is interesting. I don't recall having any codes like yours but then again my problem may never have been the alternator in the first place. I had a bad ground strap as I mentioned but replaced the alternator in the process.

If it were me I'd really look into the IBS, then the alternator.

https://www.bimmerscan.com/bmw-intel...ry-sensor-ibs/

https://www.newtis.info/tisv2/a/en/e...ttery/1LyvW9MF

"...only exchange the IBS when there is a corresponding fault code entry!"

BMW is pretty clear on not replacing the IBS unless its actually the problem. They say in one of those articles that they've tested "defective" devices that were replaced and they were fine. Unfortunately I'm not sure how to determine whether its defective or not.
thanks alot man, I'll go thru these and see if I can find another ibs
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      10-12-2017, 08:11 AM   #10
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Just start with the alternator. It sounds like the voltage regulator is giving out.The IBS will have nothing to do with your issue.
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      10-12-2017, 08:14 AM   #11
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Quote:
Originally Posted by mxchris727 View Post
Just start with the alternator. It sounds like the voltage regulator is giving out.The IBS will have nothing to do with your issue.
thanks, when i was researching the voltage increase to 18v last night i noticed that could be related to regulator. maybe ibs could also be a secondary cause, but i ended up ordering a used alternator from a 135 with 3k miles a few minuites ago from LKQ. i'll post back once i have it installed.
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      10-12-2017, 09:22 AM   #12
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BSD (Bit Serial Data line) is a bus that goes to water pump, alternator, oil level sensor. And it may also be going to IBS, I don't remember that one well. you can search here or google you will find.

Alternator has two wires that goes into it. One is thick red battery plus wire. The other is a thinner single wire that connects to the voltage regulator, this one is on the BSD bus. The ECU uses this bus to tell alternator what voltage to make its output.
I would check if you had connected this wire to the alternator.
If yes, then it is possible you have a bad voltage regulator that is making the rest of the BSD bus not work also.
You need some troubleshooting to do.

People here reported and based on documentation as well, when BSD wire is disconnected from alternator, alternator is designed to go to its own default working mode, which would make it more like regular alternators that are not controlled by ECU. So it is supposed to put something like 14V if it is not connected on BSD. With BSD connected and everything working, I have seen ECU commanding alternator from 13.5 to 14.8 Volts output voltage depending how much charge there is in the battery.

Hope this helps.
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      10-12-2017, 09:27 AM   #13
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Quote:
Originally Posted by PhaseP View Post
BSD (Bit Serial Data line) is a bus that goes to water pump, alternator, oil level sensor. And it may also be going to IBS, I don't remember that one well. you can search here or google you will find.

Alternator has two wires that goes into it. One is thick red battery plus wire. The other is a thinner single wire that connects to the voltage regulator, this one is on the BSD bus. The ECU uses this bus to tell alternator what voltage to make its output.
I would check if you had connected this wire to the alternator.
If yes, then it is possible you have a bad voltage regulator that is making the rest of the BSD bus not work also.
You need some troubleshooting to do.

People here reported and based on documentation as well, when BSD wire is disconnected from alternator, alternator is designed to go to its own default working mode, which would make it more like regular alternators that are not controlled by ECU. So it is supposed to put something like 14V if it is not connected on BSD. With BSD connected and everything working, I have seen ECU commanding alternator from 13.5 to 14.8 Volts output voltage depending how much charge there is in the battery.

Hope this helps.
hey, thanks this helps. yea i looked up the images online of teh bsd line items. yes ibs is connected to it. i checked the wires from alternator yesterday, while the voltmeter was connected to alternator + and reading 14.9v, i shook the smaller BSD wre connected to teh regulator, nothing changed in voltage. it's on there tightly. lets see what the used alternator i ordered does, hope it works lol.
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      10-12-2017, 10:54 AM   #14
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Same thing just happened to me on my 2007 X5 E70 4.8i.
Was getting a drop in voltage shortly after driving the car around. Eventually was getting high discharge messages. Had to reset the clock a few times. etc.. etc...
At such a low voltage majority of the time the battery was not being charged at all. I initially also thought voltage regulator so I ordered one. That hasn't arrived yet however I unplugged the stupid IBS blue connector on the negative terminal of the battery and all of my symptoms went away. voltage while driving was constantly around 14-14.5 volts (The way it should be! ) After a few days I plugged the IBS back in and now it dipped a bit but while driving I'm at 13.5 - 14 volts which is acceptable and a lot better than the majority of the time being 12 volts or lower only kicking on sometimes to 13 or 14 volts! From what I understand that stupid IBS connector is super sensitive and finnicky. Also check your connections on your positive and negative terminals make sure they are very tight.
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      10-12-2017, 11:22 AM   #15
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Quote:
Originally Posted by gentooguy
Same thing just happened to me on my 2007 X5 E70 4.8i.
Was getting a drop in voltage shortly after driving the car around. Eventually was getting high discharge messages. Had to reset the clock a few times. etc.. etc...
At such a low voltage majority of the time the battery was not being charged at all. I initially also thought voltage regulator so I ordered one. That hasn't arrived yet however I unplugged the stupid IBS blue connector on the negative terminal of the battery and all of my symptoms went away. voltage while driving was constantly around 14-14.5 volts (The way it should be! ) After a few days I plugged the IBS back in and now it dipped a bit but while driving I'm at 13.5 - 14 volts which is acceptable and a lot better than the majority of the time being 12 volts or lower only kicking on sometimes to 13 or 14 volts! From what I understand that stupid IBS connector is super sensitive and finnicky. Also check your connections on your positive and negative terminals make sure they are very tight.
thanks I'll give that a try today, I'll disconnect from the battery and see if it drops again.
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      10-12-2017, 12:43 PM   #16
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I suggest Disconnect the bsd line equipment one at a time and then see if the bsd errors for others get fixed. Turn off the car and ideally disconnect battery negative terminal before each disconnecting. Do not close your trunk while battery is disconnected !!! You won’t be able to open It unless you have the physical lock on the trunk. Only early years have them
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      10-12-2017, 12:51 PM   #17
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Quote:
Originally Posted by PhaseP View Post
I suggest Disconnect the bsd line equipment one at a time and then see if the bsd errors for others get fixed. Turn off the car and ideally disconnect battery negative terminal before each disconnecting. Do not close your trunk while battery is disconnected !!! You won’t be able to open It unless you have the physical lock on the trunk. Only early years have them
this gets hard because the bsd errors don't show up all teh time. they only show up if the voltage drops after alot of driving. i'm guessing they show up due to low voltage.
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      10-16-2017, 12:39 PM   #18
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Quote:
Originally Posted by nissubaru View Post
The battery just wasn't charging and would hang from anywhere between 12.1-12.4
Same...I was getting intermittent/random 2E97 Generator codes though, so figured the alternator was slowly on it's way out the door. Swapped the alternator for a new one and was getting the same ~12.3V out of the replacement unit

Out of desperation I pulled the engine mount bracket/chassis ground strap, which didn't look TOO terrible in comparison to the known bad units I've seen. Cleaning the chassis ground point and replacing the cable with a ~$6 4-gauge parts store unit finally got my voltage back in spec.

In addition to making sure you have good ground @ the factory chassis/engine mount bracket location, are there any other ground points that could be added to further stabilize voltage? Alternator housing to body? Block to firewall? Any other existing points on the chassis we can utilize?
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      10-16-2017, 02:11 PM   #19
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Quote:
Originally Posted by FCobra94 View Post
Same...I was getting intermittent/random 2E97 Generator codes though, so figured the alternator was slowly on it's way out the door. Swapped the alternator for a new one and was getting the same ~12.3V out of the replacement unit

Out of desperation I pulled the engine mount bracket/chassis ground strap, which didn't look TOO terrible in comparison to the known bad units I've seen. Cleaning the chassis ground point and replacing the cable with a ~$6 4-gauge parts store unit finally got my voltage back in spec.

In addition to making sure you have good ground @ the factory chassis/engine mount bracket location, are there any other ground points that could be added to further stabilize voltage? Alternator housing to body? Block to firewall? Any other existing points on the chassis we can utilize?
Supposedly there is an "interference suppression band" on the passengers side of the engine bay that I believe is also a ground point but this is not the main chassis ground. See this thread for details: http://www.e90post.com/forums/showth...t=ground+point

Alternatively, I believe replacing the chassis ground with a bigger thicker ground cable might be a simpler solution than adding two cables. I bought a 1 gauge marine grade battery/ground cable off ebay for $10 that I'm going to replace my old corroded strap with.

http://www.ebay.com/itm/271487589207

6 AWG 120 AMPS Continuous
4 AWG 160 AMPS Continuous
2 AWG 210 AMPS Continuous
1 AWG 245 AMPS Continuous
1/0 AWG 285 AMPS Continuous
2/0 AWG 330 AMPS Continuous
4/0 AWG 445 AMPS Continuous

Since our alternators output 180 amps I decided to go above that and do 1AWG to be on the safe side.
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      10-23-2017, 09:49 AM   #20
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Hey all, so i tried to remove the alternator this weekend, FAIL! need to remove the oil filter housing and intake manifold. horrible design actually. they have the a/c bracket on top of the lower 2 alternator bolts which make it hard to slide out. if that wasn't there, it should just come out easily. not too difficult to remove the manifold and oil filter housing, but my fat a55 got lazy and tired in a hot houston garage hahaa.

so i looked at the replacement used alternator, remove the brushes from the voltage regulator and it was easy to remove that from the alternator on the car while still bolted on. so swapped those out. the one i took out looked ok, brushes have lots left. so far driving today and pushing it, i haven't noticed the voltage spike to 18v, or drop to 12v. it seems to be a bit more steady voltage. so i'll keep pushing it this week and try to replicate the scenarios where i saw it mess up and see if it has solved it. fingers crossed!
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      10-23-2017, 11:48 AM   #21
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Quote:
Originally Posted by racermp View Post
Hey all, so i tried to remove the alternator this weekend, FAIL! need to remove the oil filter housing and intake manifold. horrible design actually. they have the a/c bracket on top of the lower 2 alternator bolts which make it hard to slide out. if that wasn't there, it should just come out easily.
Certainly a bit more of a pain than the factory service manual suggests, but perfectly doable.

The hardest part is that most of the bolts are "blind" and you have to feel them out in order to get a wrench on them; as opposed to getting eyes on them before loosening/tightening. The nice part is you can do everything from the top of the car as opposed to on your back though.

3 bolts to loosen/push aside the a/c compressor. 3 bolts to loosen the compressor/alternator bracket. 4 bolts for the alternator. That's it!

Had I known the above when going into it, the process would have only taken half as much time to complete, but it was still waaay easier than fussing with the OFH or manifold...F that; unless the gaskets need refreshing anyway, at least.
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      10-23-2017, 11:51 AM   #22
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Originally Posted by FCobra94
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Originally Posted by racermp View Post
Hey all, so i tried to remove the alternator this weekend, FAIL! need to remove the oil filter housing and intake manifold. horrible design actually. they have the a/c bracket on top of the lower 2 alternator bolts which make it hard to slide out. if that wasn't there, it should just come out easily.
Certainly a bit more of a pain than the factory service manual suggests, but perfectly doable.

The hardest part is that most of the bolts are "blind" and you have to feel them out in order to get a wrench on them; as opposed to getting eyes on them before loosening/tightening. The nice part is you can do everything from the top of the car as opposed to on your back though.

3 bolts to loosen/push aside the a/c compressor. 3 bolts to loosen the compressor/alternator bracket. 4 bolts for the alternator. That's it!

Had I known the above when going into it, the process would have only taken half as much time to complete, but it was still waaay better than fussing with the OFH or manifold...F that; unless the gaskets need refreshing anyway, at least.
ahhh Thanks. yea I got the 4 alternator boots off then I could see 1 compressor bolt. then I quit thinking there's alot more under the compressor haha. hopefully these brushes fixed it, if not I'll give this a try. I'm gonna look up the account bracket online to see where the bolts are. yea i really didn't want to take out the OFH, drain coolant, etc again. thanks , this really helps
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