What is the root of this BMW design flaw in all 3,5,7 series BMWtrunk wiring looms?

[Arthur]

Almost every BMW E39 (5-series) and E38 (7-series) and E46 (3-series)
has shorts that develop in the trunk wiring loom - all in the same spot!

Here is a picture of the uniformity of the shorts:
http://www.bimmerfest.com/forums/attachment.php?attachmentid=286651&stc=1&d=1311702112

Here is another picture from another vehicle:
http://www.bimmerfest.com/forums/attachment.php?attachmentid=287281&stc=1&d=1312154763

And another:
http://www.bimmerfest.com/forums/attachment.php?attachmentid=261502&d=1294537117

And another:
http://www.bimmerfest.com/forums/attachment.php?attachmentid=295239&stc=1&d=1317334573

And another:
http://bimmerfest.com/forums/attachment.php?attachmentid=307223&d=1325771723

And another:
http://www.bimmerfest.com/forums/attachment.php?attachmentid=200762&stc=1&d=1252530849

I could go on (and on); but we can't figure out WHAT the BMW design flaw is.
http://bimmerfest.com/forums/showthread.php?t=397245

Q: Can you tell from these pictures what the BMW design flaw is?

 

[jim beam]

Almost every BMW E39 (5-series) and E38 (7-series) and E46 (3-series)
has shorts that develop in the trunk wiring loom - all in the same spot!

Here is a picture of the uniformity of the shorts:
http://www.bimmerfest.com/forums/attachment.php?attachmentid=286651&stc=1&d=1311702112

Here is another picture from another vehicle:
http://www.bimmerfest.com/forums/attachment.php?attachmentid=287281&stc=1&d=1312154763

And another:
http://www.bimmerfest.com/forums/attachment.php?attachmentid=261502&d=1294537117

And another:
http://www.bimmerfest.com/forums/attachment.php?attachmentid=295239&stc=1&d=1317334573

And another:
http://bimmerfest.com/forums/attachment.php?attachmentid=307223&d=1325771723

And another:
http://www.bimmerfest.com/forums/attachment.php?attachmentid=200762&stc=1&d=1252530849

I could go on (and on); but we can't figure out WHAT the BMW design flaw is.
http://bimmerfest.com/forums/showthread.php?t=397245

Q: Can you tell from these pictures what the BMW design flaw is?

yeah, it's easy.

1. the wire coating has a poor grade of plasticizer*, so the coating
cracks and bending concentrated at the cracked coating will fatigue the
wire.

2. they're using an elbow bend, not a torsion bend. the stress
concentration at the surface of the wire coating is less with a torsion
bend.

#1 is a factor of the germans being too "green" for their own good and
not using good old toxic pvc. #2 is the real screw-up - they would know
that one if they'd spoken to anyone who'd been around the block or had
done their own testing.


* the plasticizer used in the wire coating is crucial to give it
flexibility. the basic polymer insulator extruded over the wire is very
brittle without it, so a plasticizer is added for flexibility. if the
plasticizer is too volatile and evaporates over time, the coating will
become hard and brittle per the original polymer, then crack when
bending stress exceeds a certain value.

 

[Paul Drahn]

yeah, it's easy.

1. the wire coating has a poor grade of plasticizer*, so the coating
cracks and bending concentrated at the cracked coating will fatigue the
wire.

2. they're using an elbow bend, not a torsion bend. the stress
concentration at the surface of the wire coating is less with a torsion
bend.

#1 is a factor of the germans being too "green" for their own good and
not using good old toxic pvc. #2 is the real screw-up - they would know
that one if they'd spoken to anyone who'd been around the block or had
done their own testing.


* the plasticizer used in the wire coating is crucial to give it
flexibility. the basic polymer insulator extruded over the wire is very
brittle without it, so a plasticizer is added for flexibility. if the
plasticizer is too volatile and evaporates over time, the coating will
become hard and brittle per the original polymer, then crack when
bending stress exceeds a certain value.

PVC wire insulation contains a lead compound. Ano-no in Europe, even for
a tiny amount in a product.

Paul

 

[jim beam]

PVC wire insulation contains a lead compound. Ano-no in Europe, even for
a tiny amount in a product.

Paul

i think that was back when they were using lead pigments - hasn't been
for a while now fwiu. and lead is a no-no here too.

besides, pvc isn't exactly healthy - i think they now use something
called "epdm". with the right q.c. and testing, there's no reason that
insulation should have degraded, and with the right physical layout, no
reason it should have been challenged even if it did.

 

[Paul in Houston TX]

yeah, it's easy.

1. the wire coating has a poor grade of plasticizer*, so the coating
cracks and bending concentrated at the cracked coating will fatigue the
wire.

2. they're using an elbow bend, not a torsion bend. the stress
concentration at the surface of the wire coating is less with a torsion
bend.

#1 is a factor of the germans being too "green" for their own good and
not using good old toxic pvc. #2 is the real screw-up - they would know
that one if they'd spoken to anyone who'd been around the block or had
done their own testing.


* the plasticizer used in the wire coating is crucial to give it
flexibility. the basic polymer insulator extruded over the wire is very
brittle without it, so a plasticizer is added for flexibility. if the
plasticizer is too volatile and evaporates over time, the coating will
become hard and brittle per the original polymer, then crack when
bending stress exceeds a certain value.

Makes me wonder about the door wiring.

 

[Arthur]

dpb wrote on Wed, 13 Mar 2013 20:15:16 -0500:

What's the age of the vehicles and condition of insulation in the area?

All the vehicles are five to ten years old'ish.

Are the vehicles in very cold or hot climates and not garaged by any
chance where such degradation could have been accelerated by extremes?

The vehicles are all over the world. Same problem everywhere.

Is there preferential failure in any given circuit(s)?

Yes. All the wires have been identified and all the circuits involved
are implicated variously, e.g.,
KNOWN LOOM WIRE CONNECTIONS:
01. Red/yellow line = 2 @ x712 -> trunk lid light (positive)
02. Red/black line = 1 @ x1191 Rear lid lock switch (positive)
03. Gray/yellow line = 3 @ 1377 -> tunk lid locking switch (open signal)
04. Brown/gray line = 2 @ x709 -> left license plate light (positive)
05. Gray/Brown line = 4 @ x311 -> zv drive (lid closed)
06. Gray/black line = 2 @ x710 -> right license plate light (positive)
07. Gray/Green -> 4 @ x311 -> zv drive rear lid (positive)
08. White/ Brown line = 3 @ x311 -> ZV to luggage compartment light
09. Brown = 1 @ x709 -> left license plate light (ground)
10. Brown = 1 @ x710 -> right license plate light (ground)
11. Brown = 5 @ x311 -> zv drive ground
12. Brown = 1 @ x1377 -> trunk lid locking switch (open signal)
13. Brown/blue line = 2 @ x1191 Rear lid lock switch (unlock)
NOTE: (majority color)/(line color)=(pin number)@(connector number -> description
Sizes are 0.35mm2===21AWG, 0.5mm2===20AWG, 0.75mm2===18AWG

Perhaps a circuit operating at high capacity relative to wiring
ampacity/insulation rating is aiding in the failure mechanism.

Mostly it's the license plate light, the central locking system, and the trunk
lid which are affected.

What does BMW say?

Same thing BMW always says.
Replace the entire trunk wiring loom every five years.
BMW Part number: 61116907260

 

[Phil Allison]

"Arthur"

Same thing BMW always says.
Replace the entire trunk wiring loom every five years.
BMW Part number: 61116907260

** Or use silicone coated wire and do it just once.



..... Phil

 

[Arthur]

Phil Allison wrote on Thu, 14 Mar 2013 16:24:59 +1100:

** Or use silicone coated wire and do it just once.

Here's a picture of the loom, laid out (on a BMW E46 3-series):
http://www.bimmerfest.com/forums/attachment.php?attachmentid=265914&d=1297298236

 

[Nate Nagel]

Makes me wonder about the door wiring.

If you have one of these cars an easy fix is if/when something like that
fails, to splice in some fine-strand wire which will likely outlive the
car. A good source for a DIYer is old Fluke leads; don't throw them out
if you bend a probe!

As for door wiring, also a common failure on many vehicles... already
had to repair the speaker wiring where it goes through the door jamb for
my Jeep Cherokee as has just about every Cherokee owner. So this isn't
just a BMW problem.

nate

 

[[email protected]]

PVC wire insulation contains a lead compound. Ano-no in Europe, even for
a tiny amount in a product.

Paul- Hide quoted text -

- Show quoted text -

And maybe you've found the root cause of the problem.
Instead of using decent wire suited to the application,
the Europeans chose to use some green hippie wire,
that not only costs more, but fails.....

 

[Scott Dorsey]

I could go on (and on); but we can't figure out WHAT the BMW design flaw is.
http://bimmerfest.com/forums/showthread.php?t=397245

Q: Can you tell from these pictures what the BMW design flaw is?

My guess is that they are using a wire that isn't designed for high
flexibility, in an application where high flexibility is important.

That looks like typical crappy automotive-grade vinyl and normal
fairly coarse stranded wire.

It's breaking in the same spot because as the snorkel is moved in and
out, most of the strees is at that one spot.

Considering that BMW has been famous for electrical problems since the
Bavaria was new, this should not surprise you.
--scott

 

[Arthur]

VinnyB wrote on Thu, 14 Mar 2013 05:24:43 -0500:

What do they typically charge for such a replacement? Let me guess:
$15,000 That makes sense. Anyone fool enough to by a BMW should be
happy to pay for that fix.

These 3,4,5 series BMWs are some of the best handling and safest
vehicles on the planet. The M62, M62TU, M54, M52, & M52TU engines
are bulletproof, and the suspensions superb.

Yet, part of owning a bimmer is fixing it yourself. Otherwise you'll
go broke with the repairs. I know of scores who have "repaired"
their trunk wiring loom - but I don't know of any who went to the
stealer to have it replaced.

I was only answering the question of what BMW says to do.
We all work on our own vehicles so we repair them ourselves.

Cost to "repair" is about $20 give or take - but the real question
is why it breaks in the first place. It looks like, from the discussions,
a combination of poor choice is insulation plus a badly designed snorkel.

 

[Bimmer Owner]

Instead of using decent wire suited to the application,
the Europeans chose to use some green hippie wire,
that not only costs more, but fails.....

Maybe. But why does it always fail at the same spot.

That can't be due to the poor choice of insulation, can it?

 

[Arthur]

Nate Nagel wrote on Thu, 14 Mar 2013 06:30:59 -0400:

As for door wiring, also a common failure on many vehicles... already
had to repair the speaker wiring where it goes through the door jamb for
my Jeep Cherokee as has just about every Cherokee owner. So this isn't
just a BMW problem.

Luckily the door wiring on these E38, E39, and E46 (7, 5, 3 series) bimmers
is just fine. It's just something wrong with the way the trunk wiring
loom is designed that makes it crack in at the same point in all these
vehicles.

Now, don't even get me started on the BMW window regulators (which
constantly break on all these bimmers!).

 

[Scott Dorsey]

Maybe. But why does it always fail at the same spot.

Because if you make a loop and you open and close it over and over again,
it will fail in the center of the loop where the angle of the movement is
greatest.

That can't be due to the poor choice of insulation, can it?

No, as you'll notice the conductors are breaking too, not just the wire.
So it's a poor choice of insulation AND stranding.
--scott

 

[Scott Dorsey]

it's not just that though - their physical routing is at fault too. if
they used a torsion bend as opposed to an elbow bend, the mechanical
strain would be spread out along the whole wire, not concentrated in one
spot.

That's true, and that might be less expensive than using proper wire. Still,
there's high-flexibility wire designed for the job, that won't break.
--scott

 

[jim beam]

That's true, and that might be less expensive than using proper wire. Still,
there's high-flexibility wire designed for the job, that won't break.

but it's bmw. they won't spend a cent on better engineering that a cent
on advertising can't brainwash.

 

[jim beam]

Because if you make a loop and you open and close it over and over again,
it will fail in the center of the loop where the angle of the movement is
greatest.


No, as you'll notice the conductors are breaking too, not just the wire.
So it's a poor choice of insulation AND stranding.

respectfully and completely disagree on that. the stranding is
perfectly fine if the insulation remains intact. once the insulation
cracks, then you have substantial strain concentrated in just one spot.
even fine wire high count stranding will break if subject to such a
failure.

the fix is both better wire insulation that doesn't become brittle, AND
re-routing to avoid the elbow bend. then you can keep using cheap wire
and don't need to spend money on the expensive hi-flex stuff.

 

[Mark]

the fix is both better wire insulation that doesn't become brittle, AND
re-routing to avoid the elbow bend.  then you can keep using cheap wire
and don't need to spend money on the expensive hi-flex stuff.

--

i had the exact same thing happen in the rear door wiring in a 95
toyota camry.

Mark

 

[[email protected]]

Maybe. But why does it always fail at the same spot.

That can't be due to the poor choice of insulation, can it?

Of course it can be. If BMW uses some hippie green
insulation that isn't as pliable as other insulation, then
the insulation will crack. We can't do a forensic investigation
from some pics that don't show how it's mounted, how
much it moves, what tensions are on it, etc. But I'd bet
that area has more bending, tension, etc than the rest of
it.