[racermp]

I replaced the alternator yesterday with a used one from LKQ, seems like it has solved the issue. fingers crossed. i drove it quite a bit yesterday and 30-40 mins this morning with heavy accel/decel. no voltage spikes or drops. i'll keep monitoring the next few days and see if anything occurs. ive made a video on the alternator change, i'll posit it up one i edit it. had to move the intake manifold, and lots of mallet hammering to get it to slide in lol. old alternator was covered in oil on the inside from the oil cooler gasket leak i used to have. probably the cause

[racermp]

f....it fell again.... took alot of driving stop and go and I'm assuming heat. hard downshift and it just dropped. restarted, fine again. f

[racermp]

so I've now disconnected the 2 lines from the IBS and have driven the car quite a bit for 2 days. no voltage drops so far.

ecu has IBS missing codes but no biggie. no current violation code 387f.

I have noticed that with IBS, I used to run 13.8-13.9. now with it disconnected, it runs 14.04 to 14.14. rarely goes down below 13.95. when braking and when you get down under 5mph, it dips down to low 13s then comes back to 14s. this happened before too. not sure if it's normal or not.

[racermp]

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.

u called it, with IBS disconnected, no issues so far. looks like IBS heats up and gives crap info to ecu.

[nissubaru]

Originally Posted by racermp

u called it, with IBS disconnected, no issues so far. looks like IBS heats up and gives crap info to ecu.

Glad to hear it, certainly isn't fun tracking down electrical issues on these cars. Thanks for the update

[racermp]

Originally Posted by nissubaru

Glad to hear it, certainly isn't fun tracking down electrical issues on these cars. Thanks for the update

Ya man it was sooo frustrating because it was intermittent and Soo odd. Voltage spike to 18v would mean voltage regulator but that didnt fix it. Plus the dme didn't really point to it. Thank you for pointing me in the right direction. Hope it helps others. I found a few other posts in different forums where they never solved it so hope this helps them

[juld0zer]

Some great info from some very knowledgeable people in this thread, and thankyou OP for concluding the thread!

In addition to all that has been said already:
- With BMW's intelligent alternator control, alternator output is fully variable, controlled by the DME based on data from the IBS and on my perfectly functioning N55 i frequently see voltage dips on my Scanguage down to 11.7v, peaking at approx 14.7v when coasting downhill in gear or within 1-2s of pressing the brake pedal
- The voltage output will peak when coasting/braking. This is part of the Efficient Dynamics and/or brake energy regeneration feature. By disconnecting the IBS you are taking away the battery data from the DME. So it cannot calculate a target alternator output without the battery temp, voltage, load, state of health etc.
- Disconnecting the IBS will make the alternator output a fixed voltage
- This is just my assumption but i believe the voltage dips below 12v you see over OBD while driving is to manage the battery state of charge. The DME aims to keep the battery at about 80% SoC. This is to allow brake energy regeneration to function because you cannot top up a full battery. So it will turn off the alternator to drain the battery deliberately while driving. (Again, this is purely my conclusion. I have no proof)
- The DME will turn off alternator output during WOT acceleration. Again, part of the Efficient Dynamics feature to minimise engine load and fuel consumption.

If your car has an IBS, please keep this in mind when troubleshooting as a lot of textbook test procedures and troubleshooting is incorrect for these cars.

PS: Wasn't there another chap here who had the same faults, also running MHD? Is there a bug in MHD? He never concluded his thread though

[PhaseP]

Originally Posted by juld0zer

- With BMW's intelligent alternator control, alternator output is fully variable, controlled by the DME based on data from the IBS and on my perfectly functioning N55 i frequently see voltage dips on my Scanguage down to 11.7v, peaking at approx 14.7v when coasting downhill in gear or within 1-2s of pressing the brake pedal

Caution here, what BMW calls "BRAKE ENERGY REGENERATION" may not be found on most E90's if any at all in the US versions. I don't remember exactly at what year and with which models and countries BMW started adding this feature, but I know my car doesn't have it being 2006. From what I had read years back, the cars that have this feature came with AGM batteries from factory since it is more demanding on the battery and AGM's are more robust.

If you see voltage below 13 volts in an E90 while engine is running, you most likely have a bad alternator, unless yours came with this "brake energy regeneration" and you have been accelerating and ecu had decided battery has enough charge to not needing urgent charging and etc.

That being said on every E90 the ECU adjusts the alternator output between 13.5 (could be 13.2 lowest don't remember exact) and 14.7 volts depending on its decision on battery charge. So between those values, alternator is working fine.

[juld0zer]

Some more good info there and clarification 👍

I only went on about IBS and brake energy regeneration because OP mentioned they had an IBS.

To identify an IBS, it will be part of the negative battery cable and looks totally different to a non IBS cable.
IBS cables are black. Non IBS are brown.
Early IBS sensors were housed in black plastic casings. Later ones made by Hella are bare.

[racermp]

So yesterday I had a voltage spike. Sat at a drive thru for quite some time. Then when I left, flooded it to get thru traffic, tcs kicked in then voltage went to 18v and stayed there, all bsd codes and issues again, had to pull over. Restart and voltage back to normal 14v.

So I guess it wasn't ibs. Damn.

I'm guessing it's heat related. I'll check dme fan I guess. So sick of this car.

[PhaseP]

I had suggested this before, try disconnecting the BSD line from the alternator. Alternator will default to working like a regular one, not under control from ECU, output will be constant something 14 volts.
If you don't get any voltage problems with this way, then it would mean something on the BSD line is causing the BSD line to get corrupted and alternator receiving shut down or max output voltage commands, incorrectly.
If that is the case, it could be any of the devices on the BSD line, or the ECU itself that is the culprit.
In your case staying at 18V and after restart going back to 14V to me indicates software issue, restart solved it.

Something to try. If with the BSD line removed your voltage problems go away, then you need to disconnect one at a time the devices on the BSD line to troubleshoot, but you told before that would be difficult. For one, water pump you should never disconnect, maybe for a very short time on a cold engine.

tcs kicked in

What is tcs ?

[racermp]

Originally Posted by PhaseP

I had suggested this before, try disconnecting the BSD line from the alternator. Alternator will default to working like a regular one, not under control from ECU, output will be constant something 14 volts.
If you don't get any voltage problems with this way, then it would mean something on the BSD line is causing the BSD line to get corrupted and alternator receiving shut down or max output voltage commands, incorrectly.
If that is the case, it could be any of the devices on the BSD line, or the ECU itself that is the culprit.
In your case staying at 18V and after restart going back to 14V to me indicates software issue, restart solved it.

Something to try. If with the BSD line removed your voltage problems go away, then you need to disconnect one at a time the devices on the BSD line to troubleshoot, but you told before that would be difficult. For one, water pump you should never disconnect, maybe for a very short time on a cold engine.



What is tcs ?

Hey thanks, I will disconnect it today and try it for A few weeks. Oh tcs = traction control kicked in because I floored it. Then voltage shot up to 18. Yea usually if it drops to 12v or goes up to 18v, I have to restart it to make it 14v again. I'll report back with how it goes with bad disconnected from alternator.

[Dockside1]

I have experienced this issue as well on and off starting back in october. The issue only occurs when the vehicle is hot under the hood. I have a new battery and replaced the alternator to no avail. However my local tuner shop diagnosed it as an issue with the mhd tune being used and recommended a custom tune. Try removing the tune from your car first. I have had no problems since and will be getting a custom tune in the near future.

[racermp]

Originally Posted by Dockside1

I have experienced this issue as well on and off starting back in october. The issue only occurs when the vehicle is hot under the hood. I have a new battery and replaced the alternator to no avail. However my local tuner shop diagnosed it as an issue with the mhd tune being used and recommended a custom tune. Try removing the tune from your car first. I have had no problems since and will be getting a custom tune in the near future.

hey thank, yes mostly happens more often when it's hot. you may be right. i removed tune. but havent' driven much plus it's been cold here lately. i'll keep mhd off to see what happens. makes sense tho. thanks man

[mattisere]

Originally Posted by racermp

hey thank, yes mostly happens more often when it's hot. you may be right. i removed tune. but havent' driven much plus it's been cold here lately. i'll keep mhd off to see what happens. makes sense tho. thanks man

Any news on this yet? I have the same issue but i'm in the UK, where believe me.. it is not hot

The car has an amplifier which was professionally installed by a high end BMW specialist in London so they know everything about the cars electrical system. Only issue is, the previous owner had it installed so I don't know who the company is to ask!

Really at a loose end with this as it makes it quite un-saleable when the time comes

[racermp]

Originally Posted by mattisere

Any news on this yet? I have the same issue but i'm in the UK, where believe me.. it is not hot

The car has an amplifier which was professionally installed by a high end BMW specialist in London so they know everything about the cars electrical system. Only issue is, the previous owner had it installed so I don't know who the company is to ask!

Really at a loose end with this as it makes it quite un-saleable when the time comes

Wonder if this has anything to do with it, do you have oil on the belt or do you see signs of the belt slipping? I have a bit from ofhg starting to give. I'll replace next week.

[FrenchX3]

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?

[racermp]

Originally Posted by FrenchX3

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?

damn yea sounds similar. mostly in hot weather im assuming?

no resolution yet. but i've hardly driven the car in the last few months, been driving my daily old land yacht (sequoia)

[hengly]

I am having the same issue. new alternator, new batteries, new serp belt. any update?

[racermp]

Originally Posted by hengly

I am having the same issue. new alternator, new batteries, new serp belt. any update?

car is sold, however check if you have any oil leaks, i think what was happening is that the belt was slipping due to oil. i fixed all the minor leaks and i didn't see that issue, however i hardly drove the car in the past 6 months. and now sold.

[juld0zer]

Stop wasting your money guys - it's normal. Seriously.

Do this test, assuming your battery is healthy and charged:
Find a long hill and coast down or gently apply the brake.
If the voltage shoots up to approximately 14.7v, this is normal. This is the brake energy regeneration/recuperation feature in action.
Next, turn the car around and accelerate hard up the hill. You will notice the voltage drop to around 12v. 11.9v occasionally. There is some acceptable tolerance in measurement accuracy. Again, another sign it is working properly - the DME disables the alternator to free up more ponies to accelerate the car.

If you come to a halt then engage reverse gear, you'll also find that the voltage "normalises". This I believe is also normal but I don't have an explanation why.

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.

The aim is to save fuel and charge the battery when fuel cut is active - coasting and braking.

The chap with the voltage spike up to 18v or an alternator that puts out increasing voltage, sounds like you need to get the car diagnosed properly. That is not normal. N54 are quite renown for it.

[PhaseP]

Originally Posted by juld0zer

Stop wasting your money guys - it's normal. Seriously.

Do this test, assuming your battery is healthy and charged:
Find a long hill and coast down or gently apply the brake.
If the voltage shoots up to approximately 14.7v, this is normal. This is the brake energy regeneration/recuperation feature in action.
Next, turn the car around and accelerate hard up the hill. You will notice the voltage drop to around 12v. 11.9v occasionally. There is some acceptable tolerance in measurement accuracy. Again, another sign it is working properly - the DME disables the alternator to free up more ponies to accelerate the car.

If you come to a halt then engage reverse gear, you'll also find that the voltage "normalises". This I believe is also normal but I don't have an explanation why.

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.

The aim is to save fuel and charge the battery when fuel cut is active - coasting and braking.

The chap with the voltage spike up to 18v or an alternator that puts out increasing voltage, sounds like you need to get the car diagnosed properly. That is not normal. N54 are quite renown for it.

I don't think E9X got the "regenerative brake". I know mine doesn't have it being 2006 make since it was introduced later on at 5 series I believe.

From what I read the models that got regenerative brake have AGM batteries due to more demand on battery and requiring more robust battery. A great number of E9X's are not AGM batteries (still high capacity though).
On my car the DME still changes the alternator voltage between 13.5 and 14.8 base on state of charge but is not disabling it.