When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Yesterday we dropped my wife's '21 GLC 300 off at the dealer for obvious misfiring, yet no CEL. It was gradual, i.e. my wife might notice it when parking (which I learned later), but would not happen again for days. Two days ago I felt it for myself when pulling into garage. Next morning I pulled out the Autel (MX900) and started the car. There were 2 stored P030385 codes (see photo, sorry for sideways). Live data showed cyl 3 misfires as I revved the engine. Turned it off, did a little digging, found multiple differently dated versions of this Xentry document (attached), called dealer, and said we were bringing it in. I showed the doc, talked to the SA, and hoped it would be something simple--perhaps a bad coil despite no P0303 (which one would expect for a bad cyl 3 coil). Car still under warranty at 42K w/prepaid maintenance and typical driving habits. Only 93 octane gas.
Sure enough, it failed the leakdown test, and is getting a new cylinder head next week. I need to do some research to see if anyone has published, much less identified what the root cause is, b/c Mercedes knows there's an issue if there are multiple Xentry bulletins. My wife loves the car, and I like it too. This is the first car she's ever had where she wants to drive the wheels off. But it raises the question of keep or sell. Will the next cylinder head will do this again down the road? Bad design inherited from the M274 or new? Overheating exhaust valves/seats b/c of carbon? Hopefully I find out and can make an informed decision. I have a decent relationship with the dealer, who is the better of the two in Nashville.
Either way folks, if your M264 starts intermittently missing, especially at low speed, don't dismiss it as a bad tank of gas or wait for the CEL. If it starts to increase, get it scanned and look for this code. I thank God to have discovered it this way versus my wife having a major breakdown on the side of the interstate at night.
Thanks for the heads up. I've got an MX-900 as well. Not experienced any misfires with either of our 2020 or 2021 GLC300 but I'll plug in every week to check. Both just under 50K miles.
Excellent question. So far I have not found much technical information beyond the Xentry documents, both of which are dated 2021. I found posts on a European site where A45 owners were having the same problem (presumably with the M260, which I think is the motor used in FWD Mercs--M264 is designation used for RWD...I may be wrong). One of the posts stated that there is a new P/N for the cylinder head. Another stated that MB extended the warranty for the M260 engine because of the valve issues. Everything at the moment is based on what others are saying, so grain of salt. One thing seems certain; given the number of customer posts for the same problem, this may not be widespread, but it is not isolated either. Now the trick is to see what the dealer is willing to divulge. This is one of Nick Saban's dealerships, and they have kept me loyal by always making things right when there was a problem or mistake. My hope is this continues and they trust me with the truth given I politely showed them a smoking gun in the form of the Xentry document.
Monday I am calling the SA to talk about it, explaining what I've read from other customers. What I am hoping for:
To hear this is a known issue corrected with an updated cylinder head
An explanation of the manufacturing/design defect
Pay for the rental car/extend the warranty as a courtesy for the trouble
A tall order, but I trust MB is aware their Consumer Report reliability ratings were dead last not too long ago, and this is a very bad thing given MB has long been an aspirational brand.
Yesterday we dropped my wife's '21 GLC 300 off at the dealer for obvious misfiring, yet no CEL. It was gradual, i.e. my wife might notice it when parking (which I learned later), but would not happen again for days. Two days ago I felt it for myself when pulling into garage. Next morning I pulled out the Autel (MX900) and started the car. There were 2 stored P030385 codes (see photo, sorry for sideways). Live data showed cyl 3 misfires as I revved the engine. Turned it off, did a little digging, found multiple differently dated versions of this Xentry document (attached), called dealer, and said we were bringing it in. I showed the doc, talked to the SA, and hoped it would be something simple--perhaps a bad coil despite no P0303 (which one would expect for a bad cyl 3 coil). Car still under warranty at 42K w/prepaid maintenance and typical driving habits. Only 93 octane gas.
Sure enough, it failed the leakdown test, and is getting a new cylinder head next week. I need to do some research to see if anyone has published, much less identified what the root cause is, b/c Mercedes knows there's an issue if there are multiple Xentry bulletins. My wife loves the car, and I like it too. This is the first car she's ever had where she wants to drive the wheels off. But it raises the question of keep or sell. Will the next cylinder head will do this again down the road? Bad design inherited from the M274 or new? Overheating exhaust valves/seats b/c of carbon? Hopefully I find out and can make an informed decision. I have a decent relationship with the dealer, who is the better of the two in Nashville.
Either way folks, if your M264 starts intermittently missing, especially at low speed, don't dismiss it as a bad tank of gas or wait for the CEL. If it starts to increase, get it scanned and look for this code. I thank God to have discovered it this way versus my wife having a major breakdown on the side of the interstate at night.
The root cause is that MB is a low quality manufacturer. It's that simple. There are far too many examples to conclude otherwise.
Drive this car until it is out of warranty then dump it. You have no assurances that the replacement cylinder head will perform better, or worse, than the cylinder head from the factory.
Have a look at the X3 or Macan as a replacement. Or Genesis or Lexus. Not a GLC though, the quality is too poor. And with X254 all powertrains have been cursed with the unreliable and expensive to repair EQ Boost 48V system.
The trouble lives on the exhaust side in these engines. Cylinder 3 sems be the one that fails the most, followed by 1. My repair paperwork stated 70% leakage, so valve practically stuck open
Mercedes well aware of the issue, and have extended engine warranties for owners with the M260 (FWD vehicles). For some reason there are fewer problems on the M264 side, so Mercedes has chosen not to extend those warranties. Yet. Cost of this repair was $12,000, so very small likelihood Mercedes ever does a recall. Too much $$ to eat.
The tech I talked to believes it to be a materials issue with the valves more so than the valve seat. He has a few of these repairs under his belt
Mileage varies, i.e. he has seen failures at 20K, and others past 75K, all with well maintained vehicles
In short, I got the same cylinder head as replacement, and this can happen again. Fortunately we have warranty until summer 2026 or 75K.
The trouble lives on the exhaust side in these engines. Cylinder 3 sems be the one that fails the most, followed by 1. My repair paperwork stated 70% leakage, so valve practically stuck open
Mercedes well aware of the issue, and have extended engine warranties for owners with the M260 (FWD vehicles). For some reason there are fewer problems on the M264 side, so Mercedes has chosen not to extend those warranties. Yet. Cost of this repair was $12,000, so very small likelihood Mercedes ever does a recall. Too much $$ to eat.
The tech I talked to believes it to be a materials issue with the valves more so than the valve seat. He has a few of these repairs under his belt
Mileage varies, i.e. he has seen failures at 20K, and others past 75K, all with well maintained vehicles
In short, I got the same cylinder head as replacement, and this can happen again. Fortunately we have warranty until summer 2026 or 75K.
Hope this helps folks
Do you have the M264? Did you report the issue to the NHTSA? Not sure if that will help, but I feel like its give us a better chance of Mercedes listening and issuing the warranty extension to the GLE. Are all models in the Emissions Warranty Extension for the GLA, GLC, and GLB's the M260 FWD motors?
Per comment by Mercedes Tips & Tricks (MB Fremont?) on youtube that posted the M260/M264 repairs, the problem is as common on M264 as M260. It is the same part causing the problem. The parts are from Covid times and supposedly fixed in 2023 per below nhtsa warranty extension post...
Do you have the M264? Did you report the issue to the NHTSA? Not sure if that will help, but I feel like its give us a better chance of Mercedes listening and issuing the warranty extension to the GLE. Are all models in the Emissions Warranty Extension for the GLA, GLC, and GLB's the M260 FWD motors?
The trouble lives on the exhaust side in these engines. Cylinder 3 sems be the one that fails the most, followed by 1. My repair paperwork stated 70% leakage, so valve practically stuck open
Mercedes well aware of the issue, and have extended engine warranties for owners with the M260 (FWD vehicles). For some reason there are fewer problems on the M264 side, so Mercedes has chosen not to extend those warranties. Yet. Cost of this repair was $12,000, so very small likelihood Mercedes ever does a recall. Too much $$ to eat.
The tech I talked to believes it to be a materials issue with the valves more so than the valve seat. He has a few of these repairs under his belt
Mileage varies, i.e. he has seen failures at 20K, and others past 75K, all with well maintained vehicles
In short, I got the same cylinder head as replacement, and this can happen again. Fortunately we have warranty until summer 2026 or 75K.
Hope this helps folks
The repair cost is so different with everyone I have talked too with this issue. There are more people on the GLE forums (M264 engine) that are experiencing this issue too. The actual cylinder head only costs $2600 (but can be found cheaper from authorized MB retailer). The labor cost is what costs the most, and the BS parts they add to the invoice that don't need to be changed or don't even fit the model of the car.
The repair cost is so different with everyone I have talked too with this issue. There are more people on the GLE forums (M264 engine) that are experiencing this issue too. The actual cylinder head only costs $2600 (but can be found cheaper from authorized MB retailer). The labor cost is what costs the most, and the BS parts they add to the invoice that don't need to be changed or don't even fit the model of the car.
Thats where they get you, by adding those BS parts, I'm hoping that with my GLC which has the extended 100k mile warranty they can replace the faulty cylinder head. I mean, I really don't see why not.
Thats where they get you, by adding those BS parts, I'm hoping that with my GLC which has the extended 100k mile warranty they can replace the faulty cylinder head. I mean, I really don't see why not.
I think it should, I believe the extended warranty for the GLC and all models but the GLE includes the cylinder head.
Today I took the GLC 300 to a dealer in Pensacola for prepaid 50K B service, and was pleased to learn from the SA that replacement cylinder heads have improved exhaust valve seats. They will confirm I had the correct one installed in Nashville. I was given incorrect information back in March. There were two GLC's awaiting arrival of their replacement. No word on whether or not Mercedes will issue a recall, but this is a quietly significant issue with the M264.
Today I took the GLC 300 to a dealer in Pensacola for prepaid 50K B service, and was pleased to learn from the SA that replacement cylinder heads have improved exhaust valve seats. They will confirm I had the correct one installed in Nashville. I was given incorrect information back in March. There were two GLC's awaiting arrival of their replacement. No word on whether or not Mercedes will issue a recall, but this is a quietly significant issue with the M264.
Thought folks might want to know...
Thanks for your update, OP. I wonder if the M254 have these improved cylinder heads with the exhaust valve seats as well, at least from factory?
Whew, that's great news. Even though I still have a year on my CPO, this issue was already making me anxious about my recent purchase of the '21 GLC300. I got away from a diesel with the highly complex emissions system to have less concerns... I wonder how Mercedes will handle those who already had to have the engine head replaced, at the owners expense in part or whole -
Very interesting ! Where did you find this ? There are no other mentions of a us warranty extension online . I called my MB dealer and they said they expect they will extend but have not heard it official yet . Where did you find it ?
Very interesting ! Where did you find this ? There are no other mentions of a us warranty extension online . I called my MB dealer and they said they expect they will extend but have not heard it official yet . Where did you find it ?
When did you contact your dealer about it? Because it was already sent out to dealers on the 9th. They should be aware of it already.
They are very much aware of it, our '21 GLC300 with 46,000 miles and 6 months out of warranty threw the CEL with all the right codes about 2 weeks ago. Took it to the dealer and started the negotiation for a goodwill warranty repair, and W140king's posting of the above letter was all I needed to get the repair covered under warranty. Picked up the car on Friday, all good (for now). Here are three pages of the invoice to show their workup (80% leakdown (!) on the bad cylinder #1) and all the parts replaced. Perfectly timed failure.
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
