This one won't work efficiently on this setup. You need to heatshield the whole exhaust portion, not just the turbo, which is the culprit. I found it easier to shield the affected components instead of the exhaust.

Ohhh ok
so then you could add exhaust wrap
that is very very cheap

This proposal would have been suitable if you needed to wrap a 3-inch pipe. However, the M256 setup could be very cumbersome to wrap with this.
End to this from my side.

I'd be concerned about the under hood aerodynamics being affected.
Disrupting the flow might cause overheating in other components.

I know that my right front tire temps always run +3-5psi higher than LF, because of the turbo / catalyst heat concentrated up there. (Six cylinder.)

Had a similar experience to others here. 2021 GLE 53 Coupe with 59,000 miles and went for spark plug replacement. Indie mechanic with 30+ years that I trust and hasn't been proven wrong (yet) showed me where the insulation was missing / bare copper. He also gave me the old harness, and showed me multiple other forums where this issue is being surfaced. $350 in parts and another $1000 in labor to replace it. He documented it with photos...and suggested that I call MBUSA for some sort of customer concession. I was hoping they'd at least share in the cost.

Hard no. I guess I was supposed to pull the vehicle from my indie and take it to the dealership. There was no formal recall. They won't reimburse anything because I didn't have the work performed at a dealership....despite this being a clear manufacturing defect.

Pretty disappointed with how Mercedes Benz handled this, a $100,000 vehicle with only 60K miles on it and a clear issues with a part. I can understand that they want all service performed by a dealship, but it's consistantly 2x the cost....

I just received a call from our experienced, diligent, trustworthy Indie repair shop, which ran into this exact issue during a routine spark plug replacement. First, the plastic boots covering spark plugs deteriorated during removal, and then the wiring harness sheathing disintegrated in their hands when trying to repair it. They did their best to splice back the wire but said the insulation around the wires is falling apart. They haven't seen anything like this since the 90's when Mercedes apparently decided to use soy-based sheathing in key wiring.

Does anyone have suggestions for getting Mercedes to cover the wiring harness replacement cost? I plan to call Customer Care tomorrow and drive right over to our local dealer.

This must be a known issue that deserves a recall, right? How do we collectively make that happen?

What is your indie quoting to fix it? Just curious.

Our indie, Mellow Motors in the SF/Marin area, came up with a good strategy. Buy the $180 wiring harness replacement from MB and he’d cut it about halfway (at the point the harness disappears into the vehicle’s abyss) and splice it in at that point. He estimated a two-hour job if done that way.




I then called MB Customer Care prepared for an emphatic fight about them doing the right thing to cover a known issue. The agent put me on hold after hearing my summary and when she came back, she said “this will be covered by our Good Will Clause”. So, our local dealer will do the full replacement and MB will cover 100% of the cost. Incredible!

This faulty sheathing issue is clearly something they know about and I imagine have flagged as a borderline recall. Just wish I hadn’t already paid $500 to replace all the rubber boots that cover the plugs. I’ll still chalk this up as a major win and have a little more love for MB USA and a lot more for Mellow Motors who ate a few hours trying to patch disintegrating wiring.

Thanks to posts like this one, I discovered before changing the spark plugs in my 2019 CLS450 (70k km) that the wiring harness in my car was in the same condition.



I had previously purchased a complete wiring harness to replace it along with the spark plugs.

Unfortunately, I wasn't aware that the connector has a constant 12V and GND. I unplugged two connectors from the coils to assess their condition, doing so with the ignition off. During the wiring harness replacement, the battery was disconnected, except for the coil connectors at the beginning... After replacing the entire wiring harness – it was a tough job, with limited access to some connectors and very little space – it turned out that when I started the car, it was running on only 3 cylinders.
Errors:


After checking the new engine wiring and connections, everything pointed to the ECU. On the working coils, one of the pins connected to the ECU had a 2-ohm resistance to ground. On the non-working ones, there was no connection.


I opened the ECU and traced the paths. It turns out that both cylinder groups (3 cylinders each) are interconnected. Three pins are connected by a thicker trace going to the PCB’s through-hole. There’s plenty of space, so I assume the manufacturer designed this part as a fuse that would burn out in case of a short circuit.


After soldering, the car started without any errors.

Additionally, I installed insulation on the intake manifold and the catalyst to isolate the coils. I mounted a fiberglass mat with aluminum foil. The installation doesn’t disturb the designed airflow, but it perfectly insulates against heat. After removing the engine cover, the temperature in that area is noticeably lower.

Regarding the flap in the front intake – I wouldn’t remove it. It naturally opens while driving. During a standstill, its absence would do more harm than good – it acts as a check valve. When the radiator fan is running, air is pushed through the engine bay towards the windshield. If we remove it, the lower resistance in that area will cause the air to blow in the opposite direction, instead of flowing over the engine.



I would suggest to all m256 owners to check conditions of the harness and replace it in advance to avoid ECU damage.

My dealer found the bad harness and replaced everything under warranty. 42 months and 42,000 miles.
I had it in for a "pre warranty expiration" checkup, willing to pay for diagnostics, and a dead backup camera.
No charge to me for anything.
Worth the diagnostics.

Does the M176 suffer from this same fate? I just got back from a trip (unplugging my 12v maintainer) and took a peek under my engine cover but didn't see any issue. I'd like to be proactive about it if it does. I have to do my sparks soon so I guess I'll find out very soon anyway.

I think this in only issue with m256.

Posting my experience. 2021 GLE53 SUV. Took it to an indie last year for spark plugs just under 50k miles. They replaced the plugs, then told me my harness appeared to be in very bad condition. Insulation wasn’t there, bare wire already corroding in many spots. Wish they saw it beforehand as their work disrupted the already fragile wires. They recommended taking it to MB. Scheduled appointment but only made it 1 day (needed to drive the car; no other choice) and it started mis-firing, check engine light flashing, etc. Limped to dealer and they diagnosed the engine harness being bad and needing replacement. They replaced the harness and turned out my ECU also got fried as a result. Replaced the ECU also and car has been fine for the past 8k miles. Fortunately all covered under warranty but clearly MB has an issue here. I’m hoping my new harness is a newer version and better quality, but sounds like I could face the same problem again. I intend to keep the car several more years and I’ll have my mechanic do a visual inspection of the harness every time I have service done.


Wishing others luck, but the more this problem is raised with MB the better chance we have that they’ll recall or provide an extended warranty on that part.

Thanks for the report.
It's a concen for me, as my 53 is out of warranty in March. (Bought breakdown policy.)

Although you needed your car, I've been told to stop driving if the light is flashing and that Mercedes will tow a car with a flashing light.

Based on your tale, I'll definitely heed a flashing light!

Good that warranty covered all.

I agree, and I'll report my bad wiring to the Feds.

I plan to keep mine for a long time.

Just to clarify, the car was ok when I headed to my destination. It was on the way back that it started running rough, followed by a solid CEL and then flashing. I immediately pulled over as I knew that wasn’t good. Restarted and light went back to solid. With my wife and 3 young kids in the car I made the conscious decision to drive it over towing it as I was about 5 miles from a dealer. Not my usual dealer, but in the end it all worked out.

I would proactively have the dealer inspect yours before the warranty is up. Maybe you’ve noticed a rough idle and that will lead them down this path. Maybe push the issue with them. It’s probably a decent enough paying job (labor heavy) for them to want the warranty work if they find the slightest thing wrong with your harness.

Good advice and I agree.
I dd just that a couple of weeks ago. See post #35 above.
I had no symptoms, but they found the culprits right away.

My understanding is that, since Germany is All About Earth-Friendly materials and recycle-ability, they used some biodegradable components. Not verified, but I saw it on the Internet.
Off topic, but the Germans prefer plastic seats over leather - "Animal Friendly."

The only ‘green’ thing MB likes is money!!! Probably squeezing as much profit out of these $100k+ machines as possible and then denying when there are rampant problems to not eat into profits.

I am hoping I got a good build tho. Bought CPO at 38k miles. Prior owner only had 1 warranty fix for a lose gas cap. My only problem was the wiring harness and now at 58k. I am prepared for things like the air suspension but fingers crossed overall.

Makes me glad my cars are a couple of generations old.

I am in the exact same boat what a nightmare. I brought it to my Indy repair man who specializes in the foreign motors for spark plug replacement, only to find out the wires in the wiring harness disintegrated so we had to change out a new wiring harness, but when he test drove it at misfired so we had to add 4 new ignition coils. When he gave me the car, he told me the engine light would still be on to take it to Mercedes just to have them turn off the light because the adaptive test couldn’t be completed. Took the dealership three weeks later. I still do not have my car they claim they were waiting for a special tool coming from Germany to do the diagnostic test, but as of recently, they were telling me now I just need anew fuel rail harness repair $1400 and very possibly but not sure yet a $10,000 job for a new engine harness. I almost keeled over. May not need the new engine harness due to false positives from the frayed fuel wire harness. Had no issues with this car until of course, after warranty and after spark job replacement. This has become a nightmare, no more Mercedes after this. I’m hoping this $1400 job does the trick to keep the engine light off. Same reply from MBUSA above this should’ve been taken to a dealership as they will not do anything for reimbursement and nothing is under recall for this car.

Have no idea what they are doing. I was able to manage repair on my own with xentry and multimeter without any special tool..

exactly why I’m 100% done with Mercedes Benz. They can’t fix anything. Their US dealerships are not equipped to support their own product. Once our GLS throws its first code, it is gone, and will be our last MB. Knock on wood, it’s been good to us, but crossing over 80k miles now, I know the clock is ticking….

Some cautionary tales about going to an Indy these days.

I've talked to (interviewed) two of the highest rated Indys in the area, and although they were full of braggadocio, they didn't know the new cars. Nope not yet.

My Indy Porsche guy advises the Dealer for newer models.

I think part of the reason is the hefty diagnostic subscription. One indy told me straight up they won't service 2020+ besides the basics because he lacked the diagnostic tools. He said it would be $36k annually.

Yes.
Plus, many fixes are downloads directly from MB.
There may pirated versions, but I'm uncomfortable with that idea.

Triumph Engineering Co Ltd; the 3 pre 1972 motorcycles that I owned had the Chinese handcuff wire looms that the rodents loved to eat. Also their electrical supplier Lucas was known as the "prince of darkness".