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For the 6-cylinder (M256) engine (450, 53, and 63), I've heard that due to the high temperature at idle, there is a high possibility that the wire harness may get burned. The solution is to remove the flex door in the intake pipe. Has it unfortunately happened on someone's car?
Yes, this is a real thing. Failure to correct could also result in a fried ECU. My MB foreman pointed it out on my M256 2020 AMG GT 53.
He took photos, apparently the heat from exhaust and turbo causes the wires to fall apart. Poor heat shielding. I was able to get MB to give me a $700 courtesy credit since this is a well documented issue across the web. My dealer quoted $1400 for repair and said they couldn't change spark plugs without repairing first as the moment you start disconnecting coil packs they fall apart.
I suggest having it inspected if your car is between 40-50K miles.
Have never seen or heard of this. Thanks for posting.
No problem, I know it affects the M256 engine usually anything 53 but may affect other models.
To be clear, this IS NOT that cam shaft position sensor issue that leaks oil and can damage your ECU which impacts my S550 Coupe and GL 550. Yet this is another known issue you have to keep an eye on.
Last edited by lexnoir; Jul 22, 2025 at 12:17 PM.
Reason: Corrected it to say IS NOT
For the 6-cylinder (M256) engine (450, 53, and 63), I've heard that due to the high temperature at idle, there is a high possibility that the wire harness may get burned. The solution is to remove the flex door in the intake pipe. Has it unfortunately happened on someone's car?
Of course it is a bad design, it is from MB. MB specializes in bad designs. This, as are many other bad MB designs, is well documented on this site.
Yup, real thing. There are other threads on this issue. Happened to me just under 50k on a 2021 GLE53 with the M256 when spark plugs were changed. The wire insulation just disintegrates and the wires become corroded. Changing the plugs disrupted everything and caused misfires. Warranty covered but what an ordeal. Hoping MB extends the warranty on this harness so I don’t have to pay out of pocket when I change the plugs at 100k.
Yes, this is a real thing. Failure to correct could also result in a fried ECU. My MB foreman pointed it out on my M256 2020 AMG GT 53.
He took photos, apparently the heat from exhaust and turbo causes the wires to fall apart. Poor heat shielding. I was able to get MB to give me a $700 courtesy credit since this is a well documented issue across the web. My dealer quoted $1400 for repair and said they couldn't change spark plugs without repairing first as the moment you start disconnecting coil packs they fall apart.
I suggest having it inspected if your car is between 40-50K miles.
Hmmm, I only heard about the spark plug harness problem on the M256.
Last edited by W205C43PFL; Jul 22, 2025 at 12:35 AM.
Yup, real thing. There are other threads on this issue. Happened to me just under 50k on a 2021 GLE53 with the M256 when spark plugs were changed. The wire insulation just disintegrates and the wires become corroded. Changing the plugs disrupted everything and caused misfires. Warranty covered but what an ordeal. Hoping MB extends the warranty on this harness so I don’t have to pay out of pocket when I change the plugs at 100k.
Do you mind linking the thread you mentioned, curious, thank you. You are not talking about this right? Sparkplug=bad harness thread on this forum
Doesn't seem like what OP is talking about.
Last edited by W205C43PFL; Jul 22, 2025 at 12:34 AM.
Apologies, I had a typo. I'm definitely talking about the ignition coil wiring harness. By the way, I just had mine replaced and Mercedes paid $700 towards the $1400 repair. I asked the tech if this is something I can expect to experience every 50K miles. He CLAIMS no they've improved the design and it should NOT happen again. Only time will tell. I did look under the hood and though I didn't pop the covers off, I did notice some new shiny new metal which I can only assume is additional heat shielding.
If anyone cares the wiring harness part number is: A2561505800
The part itself is listed as $397 (on my invoice) the majority of the cost is labor.
Maybe I misunderstood. I needed the entire engine harness replaced, but it was specifically because the ignition coil plugs were falling apart after the spark plug change. Seemed like they needed to remove quite a bit to get to all the plugs in the back of the engine, but better than a splice job. Hoping my harness is an updated part number and not prone to this in the future as I plan to keep the car awhile.
What you describe is actually the issue I'm referring to. That's not the entire engine harness, just the ignition coil wiring harness.
Here's how it works...
You go to get your spark plugs changed. They pull the ignition coil wire off the ignition coils. They start to crumble and disintegrate from too much heat exposure and lack of shielding. Your car will misfire if those wires aren't in tact. The only way to complete the spark plug change is to replace the ignition coil wiring harness.
What you describe is actually the issue I'm referring to. That's not the entire engine harness, just the ignition coil wiring harness.
Here's how it works...
You go to get your spark plugs changed. They pull the ignition coil wire off the ignition coils. They start to crumble and disintegrate from too much heat exposure and lack of shielding. Your car will misfire if those wires aren't in tact. The only way to complete the spark plug change is to replace the ignition coil wiring harness.
My coil wiring was covered under warranty.
I attribute much of this to Germany's insistence on recyclable components. Natural wiring covers and the like.
It's been a thing for decades, and unless Germany relents, it'll probably continue.
I'm all for sustainability, but then something else needs to be done to ensure heat from the turbo and exhaust don't melt wires. What happened to R&D? Mine didn't look as bad as the OP, but I was due for a tune up so, might as well resolve it.
Apologies, I had a typo. I'm definitely talking about the ignition coil wiring harness. By the way, I just had mine replaced and Mercedes paid $700 towards the $1400 repair. I asked the tech if this is something I can expect to experience every 50K miles. He CLAIMS no they've improved the design and it should NOT happen again. Only time will tell. I did look under the hood and though I didn't pop the covers off, I did notice some new shiny new metal which I can only assume is additional heat shielding.
If anyone cares the wiring harness part number is: A2561505800
The part itself is listed as $397 (on my invoice) the majority of the cost is labor.
I'm all for sustainability, but then something else needs to be done to ensure heat from the turbo and exhaust don't melt wires. What happened to R&D? Mine didn't look as bad as the OP, but I was due for a tune up so, might as well resolve it.
Yikes, I mean at least it wasn't worse as the time when soy was used.
Yikes, I mean at least it wasn't worse as the time when soy was used.
Mice loved those "eco friendly " insulted wires. My dad had to replace most of the harness in the engine compartment of his BMW after mice ate the wires.
Mice loved those "eco friendly " insulted wires. My dad had to replace most of the harness in the engine compartment of his BMW after mice ate the wires.
I only heard of Japanese vehicles have soy wires, didn't know Germans had it too, did MB have them too during the Chrysler era?
I'm all for sustainability, but then something else needs to be done to ensure heat from the turbo and exhaust don't melt wires. What happened to R&D? Mine didn't look as bad as the OP, but I was due for a tune up so, might as well resolve it.
Few things....they only "care" about the cost of maintaining a car until the day it is out of warranty. Engines keep getting hotter under the guise that a cleaner fuel burn offers a cleaner car...this is 100% incorrect as compared to an engine from even 15-20 years ago. More so an engine from 30 years ago. The plastics would pretty much go for the REALLY long haul as there was less and the heat was far lower under the hood.
Now, the engines are smaller, higher compression, tighter tolerance and more prone to break (or at least set off lights).
I can promise every single person on this form that a currently running 1972 Nova is a far more environmentally friendly car than any EV ever produced and every part of every system lasted longer (did they make the Nova in 72?)
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