2E7C - BSD data bus communications fault

veer90

Captain
Nov 16, 2016
1,000
762
25
West Nyack, NY
Ride
e90 335i 6MT
Quick writeup on my misadventures dealing with this stupid fault code

A few months ago I got randomly code 2E7C BSD comms fault. Cleared it, went away. It would come back and eventually got worse from intermittent to present all the time. It can be a royal PITA to diagnose especially if it's intermittent at first like my car.

Symptoms (in the order I started noticing them):
  • random 2E9F (oil condition sensor) fault code
  • checking oil level results in no reading, with INACTIVE displayed
  • rough idling, noticeable if you have upgraded motor mounts
  • idle hunt under certain conditions. most noticeable if you clutch in and drop RPMs to idle when moving.
  • oil temperature gauge suddenly reads impossibly high (250+ in the dead of winter with easy driving)
  • faster than normal warm up
  • water pump runs unnessarily. ~3 seconds when locking / unlocking car, full tilt when ignition on / engine off
At this point you're probably thinking the car is possessed and a part out is in order.

Explanation: the BSD or bit serial data bus system links several components together on the N54: alternator, IBS, water pump, oil condition sensor, and DME. Failure of one BSD component takes down communication over the data bus and causes other BSD components to misbehave. Proper diagnosis is only possible when the fault code becomes persistent. At which point the DME fault code memory is checked after unplugging each component, in sequence, with ignition on / engine off. Sequence and explanation courtesy of a BMW tech I spoke with who helped walk me through the process:

1. Ignition on
2. Unplug BSD component in question (I started with the alternator)
3. Clear codes
4. Wait 15 seconds and re-read codes

If code 2E7C persists, then the part unplugged was not faulty. Plug it back in and repeat steps 1-4 for all other BSD components. If all other BSD components are good, then the DME is bad (rare but it happens). According to the tech, most of the time it's a faulty water pump. Another possible culprit is damaged or corroded wiring.

Me being me, I didn't listen and replaced basically everything else first. New oil level sensor... didn't fix it. New alternator... didn't fix it. No IBS (weird how some cars have it and some don't) so didn't need to replace that. Finally replaced water pump this past weekend and the code so far is gone for good. My oil temperatures are back to normal, oil level monitoring works again, and it no longer idles funny.

I don't know enough about water pumps to say for sure what happened, but when I removed it there was coolant pooled in the electrical connector. My guess is the pump housing developed a micro crack and the pump controller said see ya. Very disappointing with just under 40k on an OE continental branded pump.
 

fmorelli

Major General
Staff member
Aug 11, 2017
3,161
2,875
0
54
Virginia
www.morelliguitars.com
Ride
E89 Z4 35i, F10 535d
In summary, score another integrated electric water pump sucks.

Thanks for the write-up. Very thorough and clear to understand. I sure hope I never have to remember that I read this ...

Filippo
 
  • Like
Reactions: veer90

SJ_1989

Sergeant
Aug 7, 2018
338
246
0
Illinoisssss
Ride
2008 E90 335i
This is why I decided to go away from making a custom harness for my drag build that interfaces with the OEM DME....damn CANbus system. It can be done and has been done, but it's expensive. I'd rather put that money toward a standalone and be done with it.
 

veer90

Captain
Nov 16, 2016
1,000
762
25
West Nyack, NY
Ride
e90 335i 6MT
This is why I decided to go away from making a custom harness for my drag build that interfaces with the OEM DME....damn CANbus system. It can be done and has been done, but it's expensive. I'd rather put that money toward a standalone and be done with it.

I don't think CANbus has anything to do with this. as far as I know BSD (bit serial data) protocol is bmw specific whereas CANbus is a general protocol for different controllers on a car to communicate with one another.
 

BrazyN54

Private
Jun 1, 2018
27
13
0
Ride
07 335i
Same thing happened to me 2E7C the BSD line would go down and I wouldn't be able to check oil level.
Long story short it was the waterpump,
It stayed on even after the car was shut off for a while, ran very loud and had a lot of current draw put excess load on the alternator.
 
  • Like
Reactions: veer90

SJ_1989

Sergeant
Aug 7, 2018
338
246
0
Illinoisssss
Ride
2008 E90 335i
It was more of a general comment I guess. Everything is so interconnected on the new cars it causes weird issues/interactions.
 
  • Like
Reactions: veer90

HanZel

New Member
Jul 6, 2019
1
1
0
Netherlands
Ride
525i Touring, 2005
Thnx, have the same problem. Changed the oil sensor but no result. aux. waterpump runs very hot doh.
 
  • Like
Reactions: veer90

dfpascarella

New Member
Sep 11, 2019
2
0
0
Ride
2006 325i 6spd
I want to verify ISB BSD two wire connection in trunk. It may have been repaired. Can someone verify the wire color positions? Does grey go to grey and the two striped wires together?one of the wires pulled out with pin. May have happened to both so I want to be sure.
 

setterlee

New Member
Jun 27, 2020
2
0
0
No IBS (weird how some cars have it and some don't) so didn't need to replace that.


Hi, I have this issue tmaybe is the water pump...

thanks for sharing this info...!!!

Let me ask you something related with the IBS. My car don’t have it too, even don’t have the blue plug to connect one... your car show any error on the DME that say the IBS is missing?


I can’t understand why some cars don’t have IBS...
 

veer90

Captain
Nov 16, 2016
1,000
762
25
West Nyack, NY
Ride
e90 335i 6MT
Hi, I have this issue tmaybe is the water pump...

thanks for sharing this info...!!!

Let me ask you something related with the IBS. My car don’t have it too, even don’t have the blue plug to connect one... your car show any error on the DME that say the IBS is missing?


I can’t understand why some cars don’t have IBS...

never had an IBS missing code. might have to do with vehicle order in ncs expert, tells the car what it has and doesn't have.
 

Tawaz

New Member
Dec 3, 2020
2
0
0
Guys thanks for all your comments will check mine also for water pump because i cant read oil level and its very annoying
 

Tawaz

New Member
Dec 3, 2020
2
0
0
And also guys i dont know if all this applies because mine is N52 ive noticed all this was for N54