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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N55 Turbo Engine Tuning and Exhaust Modifications - 335i Tuning > Voltage drop to 11.9v randomly



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      07-20-2018, 05:55 AM   #45
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Originally Posted by juld0zer View Post

For regenerative braking to work, the battery is maintained at a SoC up to 80% of its capacity. That is why we have such overspecced batteries.
...
Apparently some E90's came with brake regeneration feature. It can be checked if your vin decodes to have this option or not

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      07-28-2018, 06:45 PM   #46
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Im having the same flipping issue. I took out jb4 i changed battery with genuine bmw and registered it i changed negative cable with ibs sensor i changed alternator cleaned battery cable connections at transfer point in trunk and today driving hard testing new ibs sensor car works fine until pushing it for about 15 min and voltage goes from 13.85v to 11.9v then bsd codes come up....driving me absolutely insane. Sitting in the driveway re registered battery just cause....max ac on voltage drops to 12.9v goes back up to 13.85v....shut ac off...voltage increases to 14.35v....did this for about 30min on idle....not a SINGLE ISSUE....driving it decides to go on the frits....i cant figure out what it could be unless my battery is toast....i changed the battery because it died a while back to find theres water in the trunk....cleaned corrosion changed terminals changed starter to encounter these issues then removed jb4 because had no issues while jb4 was OFF....still had the problem....changed ibs...same problem....now sitting idling with ac on and off works fine....going to drive some more tonight...wish me luck

Last edited by jus2sikwitit; 07-28-2018 at 07:16 PM..
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      07-29-2018, 07:39 PM   #47
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Quote:
Originally Posted by jus2sikwitit View Post
Im having the same flipping issue. I took out jb4 i changed battery with genuine bmw and registered it i changed negative cable with ibs sensor i changed alternator cleaned battery cable connections at transfer point in trunk and today driving hard testing new ibs sensor car works fine until pushing it for about 15 min and voltage goes from 13.85v to 11.9v then bsd codes come up....driving me absolutely insane. Sitting in the driveway re registered battery just cause....max ac on voltage drops to 12.9v goes back up to 13.85v....shut ac off...voltage increases to 14.35v....did this for about 30min on idle....not a SINGLE ISSUE....driving it decides to go on the frits....i cant figure out what it could be unless my battery is toast....i changed the battery because it died a while back to find theres water in the trunk....cleaned corrosion changed terminals changed starter to encounter these issues then removed jb4 because had no issues while jb4 was OFF....still had the problem....changed ibs...same problem....now sitting idling with ac on and off works fine....going to drive some more tonight...wish me luck
Haha yeah man. Good luck. Hope you can have patience to find out what it is. It will help alot of people. I gave up. Since the trade in, I have yet to spend a weekend working on my car. Feels good. Feels better than driving a BMW actually. Hahaha
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      07-29-2018, 07:42 PM   #48
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Originally Posted by racermp View Post
Quote:
Originally Posted by jus2sikwitit View Post
Im having the same flipping issue. I took out jb4 i changed battery with genuine bmw and registered it i changed negative cable with ibs sensor i changed alternator cleaned battery cable connections at transfer point in trunk and today driving hard testing new ibs sensor car works fine until pushing it for about 15 min and voltage goes from 13.85v to 11.9v then bsd codes come up....driving me absolutely insane. Sitting in the driveway re registered battery just cause....max ac on voltage drops to 12.9v goes back up to 13.85v....shut ac off...voltage increases to 14.35v....did this for about 30min on idle....not a SINGLE ISSUE....driving it decides to go on the frits....i cant figure out what it could be unless my battery is toast....i changed the battery because it died a while back to find theres water in the trunk....cleaned corrosion changed terminals changed starter to encounter these issues then removed jb4 because had no issues while jb4 was OFF....still had the problem....changed ibs...same problem....now sitting idling with ac on and off works fine....going to drive some more tonight...wish me luck
Haha yeah man. Good luck. Hope you can have patience to find out what it is. I gave up. Since the trade in, I have yet to spend a weekend working on my car. Feels good. Feels better than driving a BMW actually. Hahaha
coming to the conclusion of either burnt components in CAS module or maybe recoding....excessive dialectric grease on transfer point terminals in battery compartment or distribution box on top of battery
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      07-30-2018, 09:41 AM   #49
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coming to the conclusion of either burnt components in CAS module or maybe recoding....excessive dialectric grease on transfer point terminals in battery compartment or distribution box on top of battery
could be the ecu also. the BSD line comes from the ecu and something is happening in the ecu thats tell the alternator to stop charging. i think i saw a post from one guy who disconnected the bsd line from the alternator and it didn't have issue with voltage freaking out. i didn't try it. but maybe it's worth a shot.
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      07-30-2018, 09:45 AM   #50
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Quote:
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Quote:
Originally Posted by jus2sikwitit View Post
coming to the conclusion of either burnt components in CAS module or maybe recoding....excessive dialectric grease on transfer point terminals in battery compartment or distribution box on top of battery
could be the ecu also. the BSD line comes from the ecu and something is happening in the ecu thats tell the alternator to stop charging. i think i saw a post from one guy who disconnected the bsd line from the alternator and it didn't have issue with voltage freaking out. i didn't try it. but maybe it's worth a shot.
will try this...only reason i think its the CAS module is because my comfort access on my doors dont work just keyless start and trunk work....constantly getting a code for immobilizer....ibs is controlled by CAS module so is the door handle module for comfort access...and CAS module immobilizer code cannot be erased....CAS also controls ibs sensor....which plugs into BSD.....so im almost certain its the CAS module
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      07-30-2018, 12:33 PM   #51
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Quote:
Originally Posted by jus2sikwitit View Post
will try this...only reason i think its the CAS module is because my comfort access on my doors dont work just keyless start and trunk work....constantly getting a code for immobilizer....ibs is controlled by CAS module so is the door handle module for comfort access...and CAS module immobilizer code cannot be erased....CAS also controls ibs sensor....which plugs into BSD.....so im almost certain its the CAS module
Makes sense. At this point it's hard to pinpoint exact point of failure. Changing parts seems to be the only solution. Due to it being intermittent. It definitely is a computer issue somewhere. Case or dme. I say this because something is going into fail safe. Something is triggering a fail safe to drop voltage. It's like when you get engine half power.
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      08-01-2018, 08:41 PM   #52
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Quote:
Originally Posted by racermp View Post
Quote:
Originally Posted by jus2sikwitit View Post
will try this...only reason i think its the CAS module is because my comfort access on my doors dont work just keyless start and trunk work....constantly getting a code for immobilizer....ibs is controlled by CAS module so is the door handle module for comfort access...and CAS module immobilizer code cannot be erased....CAS also controls ibs sensor....which plugs into BSD.....so im almost certain its the CAS module
Makes sense. At this point it's hard to pinpoint exact point of failure. Changing parts seems to be the only solution. Due to it being intermittent. It definitely is a computer issue somewhere. Case or dme. I say this because something is going into fail safe. Something is triggering a fail safe to drop voltage. It's like when you get engine half power.
will update once i get results if car doesnt blow up in the process lol
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      08-01-2018, 09:40 PM   #53
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I'm having the same issue as the OP. Car is in the shop now and will update if resolved.
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      08-03-2018, 11:50 AM   #54
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Quote:
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will update once i get results if car doesnt blow up in the process lol
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I'm having the same issue as the OP. Car is in the shop now and will update if resolved.
yea man i hope they find something. it will help many
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      08-05-2018, 09:34 AM   #55
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Quote:
Originally Posted by FrenchX3 View Post
Having the exact same issues with my 11' 335 with N55. I've replaced the alternator and battery. It has a new water pump in last 20k miles. In my case the voltage drops. It seems to happen when I romp on the gas but sometimes it happens for no reason at all. I have no tune..completely stock. This is driving me flippin' crazy. I have to pull over and restart the engine to get the voltage back up to 14.5.

OP have you had any resolution with yours?
I would like to get an update from this guy. I sent him a PM as well. Everyone that has tried replacing parts in this thread has been disappointed so far. He apparently had success after removing his MHD tune and there are some signs that point toward software, such as a restart clearing the issue immediately.

My car is still in the shop with a very competent tech who is going down the diagnostic path and I'm about to go down there and completely remove MHD. I have had the issue on both stage 0 and stage 2, so I mean completely uninstall it.
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      08-06-2018, 08:58 AM   #56
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Went to the shop this morning and uninstalled MHD, drove it for about 20 minutes with voltage meter hooked up, including at least a dozen WOT pulls. This would have previously caused BSD codes, loss of comm with alternator (and therefore drop to 12V battery voltage) and limp mode without fail. Without MHD, no codes, no limp mode, no voltage drops.

It only took $500 worth of diagnostic time at two shops plus this forum to figure it out, lol. Even though my tech and I are 99% sure that the tune is the problem, I'm going to reinstall MHD later to see if the issues come back. Then uninstall again to prove that they go away. Then I will reach out to MHD.
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      08-07-2018, 08:57 PM   #57
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Quote:
Originally Posted by DriveBikeRun View Post
Went to the shop this morning and uninstalled MHD, drove it for about 20 minutes with voltage meter hooked up, including at least a dozen WOT pulls. This would have previously caused BSD codes, loss of comm with alternator (and therefore drop to 12V battery voltage) and limp mode without fail. Without MHD, no codes, no limp mode, no voltage drops.

It only took $500 worth of diagnostic time at two shops plus this forum to figure it out, lol. Even though my tech and I are 99% sure that the tune is the problem, I'm going to reinstall MHD later to see if the issues come back. Then uninstall again to prove that they go away. Then I will reach out to MHD.
I uninstalled mhd. That didn't help. It became less frequent, but was still there. Especially in very hot days after driving for a long period of time.

But so far it seems like most reports are from mhd guys. Maybe some food for thought.

mhd guys are pretty helpful, I'd still try to reach out to them.

Last edited by racermp; 08-07-2018 at 09:07 PM..
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      08-07-2018, 09:33 PM   #58
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Quote:
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Quote:
Originally Posted by DriveBikeRun View Post
Went to the shop this morning and uninstalled MHD, drove it for about 20 minutes with voltage meter hooked up, including at least a dozen WOT pulls. This would have previously caused BSD codes, loss of comm with alternator (and therefore drop to 12V battery voltage) and limp mode without fail. Without MHD, no codes, no limp mode, no voltage drops.

It only took $500 worth of diagnostic time at two shops plus this forum to figure it out, lol. Even though my tech and I are 99% sure that the tune is the problem, I'm going to reinstall MHD later to see if the issues come back. Then uninstall again to prove that they go away. Then I will reach out to MHD.
I uninstalled mhd. That didn't help. It became less frequent, but was still there. Especially in very hot days after driving for a long period of time.
That's why I'm going to drive it for awhile with MHD uninstalled to see if it crops back up, then I'll reflash MHD. Agree that it's heat related, too. Wonder if there's any logic behind heat buildup in the DME under heavy load causing it to go berserk? And exacerbated by the MHD tune?

Did you happen to be running the BMS cowl filters with the factory cowl removed?
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      08-08-2018, 06:58 AM   #59
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That's why I'm going to drive it for awhile with MHD uninstalled to see if it crops back up, then I'll reflash MHD. Agree that it's heat related, too. Wonder if there's any logic behind heat buildup in the DME under heavy load causing it to go berserk? And exacerbated by the MHD tune?

Did you happen to be running the BMS cowl filters with the factory cowl removed?
No I had stock cowl. Here's one thought I did have but I never checked. There's supposed to be a fan in the ecu box. In the bottom, towards firewall. Maybe it's starting to die out or clogged?
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      08-08-2018, 08:00 AM   #60
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That's a good thought. I'll check that out. It should throw a code if the fan quits altogether, but could be blocked by cobwebs or something. I wonder if DME temp can be monitored.

Thanks for continuing to engage on this even after you sold the car, lol.
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      08-08-2018, 10:04 AM   #61
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That's a good thought. I'll check that out. It should throw a code if the fan quits altogether, but could be blocked by cobwebs or something. I wonder if DME temp can be monitored.

Thanks for continuing to engage on this even after you sold the car, lol.
Haha no prob. I still have my N55 X5 so I'm active. Yeah solving this will help quite a few.
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      08-09-2018, 03:51 AM   #62
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. I wonder if DME temp can be monitored.
One of the INPA status screen (at the "analog" section) show the DME temperature.
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      08-26-2018, 05:55 PM   #63
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UPDATE - I've driven for about 2.5 weeks with MHD uninstalled and haven't had any limp mode. Had a central registry error that I think was due to battery registration being lost during the limp mode craziness, so re-registered battery and it hasn't come back.

Then decided to reinstall MHD stage 2+ on Thursday (still v1.24) and BSD codes immediately came back with WOT pulls. However, it didn't go all the way to limp mode this time, I think due to the milder temps we're having, furthering the idea that this is heat dependent.

In the freeze frame data from Carly, the thing that stands out to me is voltage readings of 40-60V at the moment codes are set off. How is that even possible? I sent an e-mail to the MHD guys this morning hoping for some assistance troubleshooting. Stay tuned!
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      09-15-2018, 01:48 AM   #64
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Wow.. you guys are still having this problem?
I had it with no MHD but latest BMW software. In the end i just stopped monitoring the voltages because it was causing unnecessary anxiety. If no control units log undervoltage faults and everything else behaves normally, i just put it down to part of the brake energy regeneration behaviour. The more frequently the car is used for medium to long journeys, the more likely it will occur due to the battery being maintained at a higher SoC.

But those of you with MHD and experiencing limp mode etc, that might be worth discussing with MHD.
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      09-15-2018, 11:28 AM   #65
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Yeah, I'm still dealing with it. It can happen with or without MHD, but mostly with. I reached out to them and the suggestion was to look for a bad ground, but I just haven't had time yet.

I think our problem is the same, but yours hasn't progressed to the point of limp mode. Sometimes I get the BSD codes only without limp mode, which causes the alternator to stop producing voltage until a shutdown/restart. But the more I watch the other codes I'm getting, the more I think the BSD codes are a red herring. Yesterday, for example, I got a limp mode with BSD codes, but also about 15 other codes from various sensors (wheel speed sensors, steering sensors, etc), all saying that there was over voltage. Freeze frame data confirms that there was at least a split second of over voltage.

As it only happens when it's hot and under heavy load, it leads me to believe that there is a short or insufficient ground somewhere that only surfaces under those conditions. My two front running ideas are:

1) Main engine ground strap going bad
2) Battery positive to fuse box connection going bad; there was a recall on this for over 500k E9X cars, but dealer says mine is not included.

Thanks for the reminder. I'm going to look at the ground strap today as it's easier and cheaper.
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      09-15-2018, 10:00 PM   #66
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Well, the ground strap wasn't the problem. Replaced it with a 4 gauge cable from AZ, then went straight out and got limp mode within a couple pulls.

So I broke down and pulled the fuse box to inspect the positive battery cable connection. Hard to say for sure, but it does kind of look like a bit of discoloration on the terminal. It's still tore apart, but I will try to make the connection tighter tomorrow and see what happens.

I'm curious, has anyone else having this problem had the recall done for the battery to fuse box connection?
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