amegren

Good day,

I own a CLS 450 4Matic for about 2 years and at 60 K k/m for now. (The car was bought on May-2020 first owner).

While doing the regular maintenance at 60 K K/m and after changing the spark plugs i started the car at the workshop and the engine was shaking so hard and the check engine light was on the dash.

so shutting down the engine and the workshop engineer plugged in the diagnostic device and the following codes was thrown:



Diagnostic codes



Diagnostic codes

the engineer who’s working on the car have stated that the wiring harness has a short circuit due to the copper wiring covers was so dry which made it to start falling out the copper itself.




the wiring harness is inflexible just like the car was being used for a very long period of time.

Have anyone faced a similar problem regards the wiring on the new M256 inline 6 cylinder engines? What do you guys suggest regard fixing the problem ?

all of your comments and help are much appreciated.

jaylee78

I had a very similar problem with my car. I own a 2019 X290(AMG GT 4Door 43) with M256 engine and I checked-in for Service B after 60,000km mileage.
Engineer had replaced all spark plugs and changed oil and all other regular stuff.
After I checked-out of the service center, I drove around 100km and the car started shaking and engine light was on.
I immediately rechecked-in and the engineer said that the ignition wiring(harness) and coil had been actually 'burned'.
They replaced wiring and coil with new sets but the problem still exists and they are now replacing the ECU since the 'burn' might have affected it.
I am quite sure that replaced new spark plugs(genuine parts) are the cause of the problem(since the old ones never caused a similar problem) but engineer's denying it.

Were you able to fix the car? I hope replacing ECU can fix the problem but I believe the real issue is the replaced spark plugs.

amegren

Thank you for your reply and i hope that after changing your ECU everything will work again.

can you please tell me whither you did the fixes in an authorised dealer or in a workshop? And please can you update the thread after changing the ECU if the problem still exist or not ?

regards.

konigstiger

Replace harness, clear/pull codes to see if any return. Provide VIN if you need part #.

jaylee78

I reside in South Korea and one of the Authorized(official) Mercedes service center is doing the fixes since I still have my warranty left. I will reply on how the ECU replacement has gone thru.
How about your car though? Did they replace the harness and the problem was fixed?

amegren

thank you for your reply and i hope that your car will be fixed!

the wiring harness has been replaced but with a used one taken from an E or S class 450 (same engine) but even though the problem still exist. I asked the authorized dealer here (Saudi Arabia - official dealer) to provide me with a new one but they said that it needs to be manufactured (will take up to 3 months) so i took the burned wiring to another specialist which fixes the wires and even though the problem still exist.

for now i took the car to another mechanic that has the all the required software/hardware equipments and they suggest a re-diagnosis process starting by replacing the spark plugs with a new set and checking the coils and the ECU .

will keep the thread updated once i have a reply from the workshop.

jaylee78

First of all, I hope the mechanic can fix your problem with new sets of sparkplugs, coils and harness.
I and my authorized mechanic are still waiting for the 'go sign' for the new ECU from Germany Headquarter. (they replaced the old ECU with brand new one but it seems that if ECU is changed to new one they need some kind of authorization from HQ to get the ECU start functioning)
But I like mentioned earlier, I dont think the problem will be solved by replacing ECU. I did alot of web search here in Korea and found out that there are number of CLS450 or AMG GT43 owners here that suffered from similar problem and some were able to fix the problem by actually replacing the cylinder head(which takes time and money).
Anyhow, I will make sure to leave a post how things go after resetting the new ECU. Also, I will appreciate it if you can feedback to me with your situation as well.
Thanks.

jaylee78

First of all, I hope your workshop can fix your car's problem by replacing spark plugs, coils, etc.
My engineer has replaced the old ECU with brand new one last week but he told me that Mercedes HQ in Germany has to authorize some code to make the new ECU start functioning.
Engineer and I are still waiting for the authorization.
But like I mentioned earlier, I don't think replacing ECU will solve the problem. I did a lot of web search about this issue here in Korea and I found more than a dozen of CLS450 and AMG GT43 owners with similar problem.
Some were able to fix the problem by replacing Cylinder Head(shown below. I just googled any image and our engine obviously has 6 cylinder), but not by replacing harness sets, nor coils, nor ECUs.

Anyhow, I will let you know how the ECU replacement went next week (if ECU replacement doesn't work, I will tell them to replace cylinder head). Please tell me how your problem is going too. Thank you.

dagger22

Hi guys, any updates so far on your ongoing issues? did you manage to fix it?
thanks.

amegren

yes all fixed by replacing a new set of coils and spark plugs along with full a new ECU with full wiring harness 🙂.

the authorised dealer here told me that they have to inspect the ECU wiring harness before changing the spark plugs on all M257 engines since they tend to dry due to overheating from the exhaust placement on M257 configuration, if the wiring harness is dry and inflexible, the will replace it and then replace the spark plugs .

Airman966

Hello,
i had the same exact engine shaking issue with the engine light flashing just 1500 km after the 60K service at the authorized dealer.
towed the car back to them.

seems like changing the spark plugs is the cause for all of this.

any advice is appreciated

Thanks.

AllPhonesAretap

Not trying to be a smart A$$ but check and make sure that all the ignition coils are plugged in. Then, take a test light and make sure that you don't have any blown fuses from the electrical mishap, sometimes it's that simple

PlatinumPartsIQ

Hi , this is a common problem with this engine , in the previous year I faced this problem with so many vehicles , the problem was that mercedes didn't know this problem and i recently discovered that new part number for the wiring harness that is updated and have no problems at all , if you still have the problem please send me the vin number & i will be more than happy to provide you with the new parts number that have no issues

regards

kdub

Do you know if the new part was used in later models of the CLS 450? I have a 2022 - curious if it was sorted out by then. I believe the original post had a 2019.

Hayk33

I had my 2019 CLS in for servicing at 60k miles. They changed the spark plugs, oil, air filters, etc. I drove the car to work and then home. The following day we left for vacation. When I got home I started my car and the engine was shaking and knocking. So I cut it off and had it towed to MB of Richmond where I purchased the car. The car has been there now for 8 months as the parts are on backorder. It needs a wiring harness and it needs an ignition coil. The backorder is open-ended with no date in sight. I love Mercedes Benz, I don't think I can drive another car. My last 4 cars were bought from MB of Richmond. My question is has anyone with this same problem gotten their car back? If so was the car running properly? I'm concerned that it can't be fixed. If that is the case is there any recourse?
Lastly, does this wiring harness defect apply to all 3L V6 motors produced by MB as I'm looking at an S 500? I don't want to get burned twice.

Thank you for any response, I'm at a loss on the car I feel like I'm going to take a bath for the sale price. Any reassurance would be appreciated.

kdub

@Hayk33 - did you have an extended warranty? Seems odd they replaced the spark plugs and immediately after this issue popped up.

Hayk33

Yes, I bought the extended warranty. I've read in this forum and others that it is a common problem after the spark plugs are changed.

kdub

Do they extend your warranty for the 8 months it’s been sitting? I just bought a new cls 450 in October 2023 - debating if I should get an extended warranty. I have noticed a slight engine shake / wobble at low idle - need to get her in the shop. Just got a recall notice on the 48v ground - so will try to get two birds with one stone.

Hayk33

I do have the extended warranty in VA the law requires them to extend the warranty while it's in the shop. In my opinion, it's important to get an extended warranty because an electrical problem can be 5 figures. I need to look into it further if I find that all the V6 have the same wire harness issues I will get a S 580. Because I don't need any headaches. I think MB is aware of a widespread problem and working to fix it as it might involve a ton of models. From what I have read the wire harnesses are slightly short and they corrode because they are vulnerable to moisture.

Fran D

[QUOTE=PlatinumPartsIQ;8880896]Hi , this is a common problem with this engine , in the previous year I faced this problem with so many vehicles , the problem was that mercedes didn't know this problem and i recently discovered that new part number for the wiring harness that is updated and have no problems at all , if you still have the problem please send me the vin number & i will be more than happy to provide you with the new parts number that have no issues

PLEASE HELP! SAME ISSUES PLIGS COILS INJECTORS CHANGED STILL MISFIRE. THIS IS A NIGHTMARE

Omarbedair

I am taking my car to the shop for 60k km maintenance soon and I have cold feet. I would appreciate if you check my VIN and let me know if I need to be ready with a part number…WDD2J5KB0LA051729
TIA