What is the root of this BMW design flaw in all 3,5,7 series BMW trunk 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:

Here is another picture from another vehicle:

And another:

And another:

And another:

And another:

I could go on (and on); but we can't figure out WHAT the BMW design flaw is.

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

[dpb]

...

Not unequivocally, of course not, but it would appear likely a temperature/time-hardening of the insulation combined w/ the flexure point eventually fatigues in that general area.

What's the age of the vehicles and condition of insulation in the area? Are the vehicles in very cold or hot climates and not garaged by any chance where such degradation could have been accelerated by extremes?

Is there preferential failure in any given circuit(s)? Perhaps a circuit operating at high capacity relative to wiring ampacity/insulation rating is aiding in the failure mechanism.

What does BMW say?

[jim beam]

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]

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

Paul

[Paul in Houston TX]

Makes me wonder about the door wiring.

[Arthur]

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

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

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

Yes. All the wires have been identified and all the circuits involved are implicated variously, e.g., KNOWN LOOM WIRE CONNECTIONS:

1. Red/yellow line = 2 @ x712 -> trunk lid light (positive)
2. Red/black line = 1 @ x1191 Rear lid lock switch (positive)
3. Gray/yellow line = 3 @ 1377 -> tunk lid locking switch (open signal)
4. Brown/gray line = 2 @ x709 -> left license plate light (positive)
5. Gray/Brown line = 4 @ x311 -> zv drive (lid closed)
6. Gray/black line = 2 @ x710 -> right license plate light (positive)
7. Gray/Green -> 4 @ x311 -> zv drive rear lid (positive)
8. White/ Brown line = 3 @ x311 -> ZV to luggage compartment light
9. 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[s])/(line color)=(pin number)@(connector number ->

description Sizes are 0.35mm2===21AWG, 0.5mm2===20AWG, 0.75mm2===18AWG

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

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

[Phil Allison]

"Arthur"

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

.... Phil

[Arthur]

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

Here's a picture of the loom, laid out (on a BMW E46 3-series):

[VinnyB]

On Wed, 13 Mar 2013 23:45:12 -0500, Paul in Houston TX wrote in Re Re: What is the root of this BMW design flaw in all 3,5,7 series BMW trunk wiring looms?:

Makes me wonder about BMW.

[VinnyB]

On Thu, 14 Mar 2013 05:16:26 +0000 (UTC), Arthur wrote in Re Re: What is the root of this BMW design flaw in all 3,5,7 series BMW trunk wiring looms?:

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.

[Nate Nagel]

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

[trader4]

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]

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:

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]

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:

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]

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.

--scott

[jim beam]

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]

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

Mark

[Ashton Crusher]

Exactly!!