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Brake Wiring harness chafing?

14K views 36 replies 11 participants last post by  jenkinskg 
#1 ·
My brake control board, wiring harness, and vacuum pump failed about 4 months ago and were replaced under warranty. Some of the postings about the failure and repair hinted at a known issue with chafing on the wiring harness eventually leading to a short in the wiring that cause the whole subsystem to fail.

I was never able to get more info about the location of the wiring and what we might do to prevent the short from happening. Is anyone on this excellent sub-forum aware of this issue and can suggest where on the car I might be able to apply some preventative measures?

Thanks in advance, RG
 
#2 ·
Unless the ED brakes are markedly different than the ICE version (don't think they are) this would potentially apply to all smarts of your model year.....

Did you report the issue to the NHTSA as a safety problem? I don't recall seeing the whole brake system failure mentioned before. :)
 
#3 · (Edited)
The ED brakes are the same except that they use an electric vacuum pump instead of engine manifold vacuum to provide the power assist. While a failure of power assist (brakes or steering) should not be considered something dangerous, it seem that in these days of a low-skill driving populace it is - such as those Chevy keyswitch defects causing fatal accidents simply from power steering or braking going of when the engine shut off.

I suspect in the case of a 2000 pound Smart ED, braking is still easy without power assist but I haven't tried it yet.

But yes, I think that NHTSA should definitely be investigating this. Rob should contact NHTSA. Presumably they have a consumer complaint site...
 
#5 ·
My brake control board, wiring harness, and vacuum pump failed about 4 months ago and were replaced under warranty. Some of the postings about the failure and repair hinted at a known issue with chafing on the wiring harness eventually leading to a short in the wiring that cause the whole subsystem to fail.
Yes. My A/C failed due to wire harness chafing. While they replaced the compressor, I'm not sure it actually failed or it was a wrong initial diagnosis. They did not replace the harness, but only found the chafing point and spliced the worn-through wire. I hope they did something about the harness chafing too.

They also replaced the charging receptacle and its harness - claiming in a follow up inspection that it was wearing through somewhere. They weren't able to provide me with the old harness though - claiming that it was already thrown out. I tied the new charging harness clear of any possible rub points myself when I got home.

Presumably, what car syatem fails is entirely dependent on the particular wire in the harness that gets worn through.

I will call my dealer and ask if I can talk to the actual service technician who did the repair to find out where this chafing point is - hopefully he will remember.

Chafing wiring is something I's expect in a Chinese or Russian car, not a German one.
 
#14 · (Edited)
Very interesting! The frame on the right side of the engine compartment is also where the charging receptacle wiring on my car were also found to be chafed in addition to the unspecified wiring harness chafing that disabled the A/C.

After I got the car back, I secured the charging wire harness better by tying it to the stiff A/C refrigerant lines that go through this area so it is not rubbing on the car frame.

I think is it time to issue out own "service bulletin" and recommends every ED owner check all wires that are routed along the right side of the engine compartment for wear.

The service guy (or gal) wrote quite a detailed report. I wonder if all MB service tech's do that. I'll see if there is comparable documentation for my car.
 
#18 ·
Very interesting! The frame on the right side of the engine compartment is also where the charging receptacle wiring on my car were also found to be chafed in addition to the unspecified wiring harness chafing that disabled the A/C.

I think is it time to issue out own "service bulletin" and recommends every ED owner check all wires that are routed along the right side of the engine compartment for wear.
With ED representing such a small production run the few reports of chafing on SCoA is alarming! Has anyone filed with the NTSB or the likes to raise the awareness and perhaps trigger a TSB or Recall?


This link will get you started . . .

https://www-odi.nhtsa.dot.gov/VehicleComplaint/
 
#19 ·
Another question... what do you think the tech who wrote the report is calling the "right side trunk panel" By "trunk" I assume he is referring to the space behind the seats and by "panel" is he referring to the interior right trim, or the outer body right quarter panel? I recall they told me that they had to remove the quarter panel to replace the charging recptacle/harness unit, and also, possibly, repair the harness to the power control unit.

So, to fully inspect this part of the wiring harness, some body disassembly may be needed.
 
#20 ·
I had some time today so I poked around in the engine compartment and underneath as well. I didn't see anything really worrying in my ED that has done 12.5k miles in 17 months since I purchased it with 10 miles on the odometer.

What I did see was a cable on the right (passenger) side that was pressed against a tube and wearing the insulation a bit. I put on some split loom tubing to protect it. Here are before and after photos. This is from the rear of the smart looking forward. This area is on the right, pasenger side of the motor bay.





From underneath, to the right side of the motor, are wire bundles that are exposed. They don't chafe on anything, but could potentially be damaged by snagging something while being driven. I didn't really have a better alternative than to just put some split loom tubing on it - that won't protect it if I really catch something heavy but it should keep the wires in better shape from gravel and rocks.

Again, before and after:





Sorry for the changing perspective on these last two pictures - it was hard to take a cell phone pic with the limited room I had underneath. The exposed wires are at the far right in the "before" picture, and are centered in the "after" picture after I put the split loom tubing on.
 
#29 · (Edited)
The wire harness wearing is occurring somewhere along the wiring harness between modules and controls in dashboard area and the motor compartment. A lot of the wiring is not-so-tidily packed into area behind the plastic interior panel behind the passenger seat where the drivetrain control unit and related connectors is located (see pages 62 and 63 of the general service info primer posted in a sticky above). So, I have a strong suspicion that this is the area where all the wiring wear problems are happening.


If you could remove this panel (the whole panel, not just the taillight bulb access door) and take some pictures of the wiring, it would be a greatly appreciated by everyone here!
 
#30 ·
OK. Cause of wiring chafing found and fixed!

I removed the interior panel. It snaps right off and if I knew it came off this easily I would have done it sooner. The wear point on my Smart and probably other 451 ED's is a rather sharp turned-up edge of steel around a "window" in the steel bodywork used to access the taillights (photo). The repair that was done at the MB dealer last year is the black tape "blob" in the bundle. The repair tech's method of preventing a recurrence seems to have been to remove some slack wire from this congested area by pushing the wire bundle through the rubber gland (bottom of photos) so the repair is now below this sharp edge.

My repair for making sure it does not happen again was to pad the sharp edge with adhesive foam rubber overlain with duct tape, and also wrap the wire bundles with electrical tape near the rub point. I also zip-tied some wire bundles together. See the second photo.

You can also probably do this repair through the taillight access door, but taking the whole panel off is easy enough and allows a thorough inspection and room to do the repair. Just make sure to engage the button-and-slot attachment in the lower rear corner of the panel when replacing.

I strongly recommend that every 2013-15 Smart ED owner go out and check this area on their Smart ASAP!
 

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#33 ·
Okay, thanks to the posts in this thread and Yinzer's photos, my son and I attacked this issue and did a preemptive strike before a problem occurred. We used quarter inch split loom tubing as you can see in the photos. On the coupe we did remove the entire panel. As a point of info, there is one Torx screw to remove. The rest of the panel just pops in/out via plastic clips.

On the coupe we used a little tubing on the actual wires, but then found out how easy and effective just putting it around the metal opening would be and that's all we did on the cabriolet.

On the cabriolet we just accessed the problem area via the small panel. Since we saw how nicely the tubing worked, we saw no need to remove the whole panel. Cost for the job - around a buck.

Len
2014 EV Coupe 18,000 miles
2014 EV Cabriolet 13,500 miles
 

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#34 · (Edited)
I'm bumping an old thread. While perusing my ALLDATAdiy Smart manual, I found the service bulletin for the chafing problem, It appears that a known problem causing chafing point is at a different location than what I thought. The bulletin includes a long list of fault codes associated with this chafing problem - but the important part is the first page and the photos from the bulletin which are included below:
Text Font Line Parallel Document
Tire Automotive tire Auto part Automobile repair shop Automotive wheel system
Tire Auto part Automotive tire Pipe Bumper
Auto part Vehicle Car Hood
Rust Auto part


Inspecting this area requires getting the car up on stands and getting underneath it.
 
#35 ·
Thanks for posting this. From the sounds of your post, you haven't checked yours yet have you? I'm due for service on mine this spring. Have to get under there and take a look. I don't recall anyone on the forum mentioning having had a problem there, have you? Did the bulletin give a fix or something to do to keep there from being a problem?

Len
2014 EV Coupe 19,500 miles
2014 EV Cabriolet 16,500 miles
 
#36 ·
The only fix specified in the bulletin was just to repair any broken wires using any of the MB-approved methods. I would hope the service tech would also care enough to add padding or relocate the rubbing part of the wire harness to prevent a recurrence - but I guess we can't assume that, eh?

I now know why they also replaced the whole charging receptacle and wiring when they repaired the harness chafing on my car. That orange-sheathed cable in the pictures is the AC power cable to the on-board charger.

I'll inspect mine soon when I get a chance.
 
#37 ·
My car now many miles later gives me a no start no charge HV service errors.
I moved the wires a little, tryed again and starts charges fine now.

Drove it to work again, I will be looking around for chaffing again, my rear hatch is super dirty from city driving etc so I am not sure how to safely clean it up to allow me to look over the wires.
I do not want to add water to my electical sysstem issues.
 
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