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Shop came back and told me $18,000!!! That is insane. Guess we have to dump the car, even though we still have payments on it. I can't believe a $65,000 care can have this type of issue, a known issue I am finding out, at under 70K miles.
Guess we have to take the full loss and figure out how to get another car.
I thought I saw something about a recall or extended warrantee on valves. I could be, most likely wrong. But how do you know the cylinder and not a valve is causing the problem. Have you tried erasing the code and seeing how long it takes to come on? Does the engine make any noise? Has it been drinking oil? I'd bet if you scoped every M278 you're going to find cylinder walls with some scoreing.
My two cents worth, (and since the government is no longer minting pennies) is worthless. I'd erase the code and wait to see how long it takes to come on. Then just keep erasing it if it botherd me or get a piece of black tape and put it over the light and run it. What are you going to do ruin the engine? Then when it hammers and knocks so bad your neighbors can hear you a block away have a salvage yard engine installed. As my children were taught in school in the late 80's, Reduce, Reuse, Recycle.
I thought I saw something about a recall or extended warrantee on valves. I could be, most likely wrong. But how do you know the cylinder and not a valve is causing the problem. Have you tried erasing the code and seeing how long it takes to come on? Does the engine make any noise? Has it been drinking oil? I'd bet if you scoped every M278 you're going to find cylinder walls with some scoreing.
My two cents worth, (and since the government is no longer minting pennies) is worthless. I'd erase the code and wait to see how long it takes to come on. Then just keep erasing it if it botherd me or get a piece of black tape and put it over the light and run it. What are you going to do ruin the engine? Then when it hammers and knocks so bad your neighbors can hear you a block away have a salvage yard engine installed. As my children were taught in school in the late 80's, Reduce, Reuse, Recycle.
Good luck.
Bob C
There was an extended warranty on it, but that’s now expired. The problem is we just didn’t drive it enough to have the issue happen before the 10 years was up.
Strange thing is I asked them if they scoped it and they said they did and it didn’t look bad but the misfires and combustion or whatever they were saying is causing the engine five misfire.
I’m fine with driving it. I just don’t know what will happen as far as will it. Just stop on the highway. Will the engine seize up what actually will happen if I don’t repair it?
Before I took it in, and I need to pick it up, there was no jerking no issues no nothing. It was just the light.
I can only go by what they told me and they said it was a cylinder. I can ask him about the valve.
Last edited by Squatting Hen; Feb 18, 2026 at 11:25 AM.
Back in the day, everytime you went to the shop it was a Franklin ($100). Nowadays, every time it's a Cleveland ($1000). Ask the shop if they erased the code? If they didn't find an OBD II code reader and erase it yourself. No need to pay a shop to do that for you.
Today everything runs so lean almost anything can cause a misfire. Just for sh**s and giggles, I'd pick up some MMO or SeaFoam and run it through. The thought is to clean injectors and upper cylinder lubricant. Maybe snake oil, I don't know. Won't do anything for carbon on intake valves that would disrupt/impede air flow as these are direct injection engines.
Maybe ask your shop if the spark plugs are properly indexed? Just shooting in the dark, but anything that might cause a misfire.
I've also read where the wrong oils can cause pre ignition.
Another thought is to have a shop pull/disable the oil pressure solenoid. A fuel saving device that reduced oil pressure, IE parasitic energy, at lower rpm. I doubt you'd even notice any difference in fuel economy and piston cooling oil would be constant. Lots written about it.
As for running it. Maybe others can weigh in. I don't see it just seizing up without warning.
s500 GL450 GL63 Z71XL Yukon 67 396 SS velle 68 Vert Camaro 69 RSSS Vert Camaro 75 Blazer
First thing I would do is take it to another shop for a second opinion. I don't trust 90% of shops out there, and that's why I do my own work. My friend asked me to check his car because a shop told him that he needed to replace the transmission which would cost $12,000. He had brought it in because of a severe transmission oil leak. Well, I check it for him and the only thing that was causing the leak was that the single center bolt to the transmission output shaft had backed off. I was only about 45 minutes of labor.
s500 GL450 GL63 Z71XL Yukon 67 396 SS velle 68 Vert Camaro 69 RSSS Vert Camaro 75 Blazer
Can you share with us the CEL code? Also, a cylinder failing can mean a lot of thing like valve, rings, pistons, etc. What exactly did he say was needed to be replaced?
Can you share with us the CEL code? Also, a cylinder failing can mean a lot of thing like valve, rings, pistons, etc. What exactly did he say was needed to be replaced?
I agree with not throwng good money after bad. I also don't trust shops especially service managers that are commission compensated on the gloom and doom they sell. If it were me, the only thing I'd spend money on is a good code reader then educate myself on any codes that pop up. Then run it till I had a cloud of smoke like Uncle Buck or the engine could drown out the neighborhood garage band.
I agree with not throwng good money after bad. I also don't trust shops especially service managers that are commission compensated on the gloom and doom they sell. If it were me, the only thing I'd spend money on is a good code reader then educate myself on any codes that pop up. Then run it till I had a cloud of smoke like Uncle Buck or the engine could drown out the neighborhood garage band.
Good Luck with what ever you do.
If I knew it would last another 24 months, I would for sure just keep it and drive it. We don’t drive much anyway, maybe 5k miles a year.
I've seen them as cheap as $23 on Amazon that says they can erase codes in the description. Do a little searching, a little reading on their functions. You'll find one for less than a shop will charge you just to plug it in and read it. However, most Auto Zones, O'Reillys, Advance Auto, etc. will read for free. Just roll in and tell them you have a check engine light and ask if they could read the code then erase it. Nothing ventured, nothing gained.
Also, If I was a betting, I'd double down on it lasting 2 years at only 5,000 miles a year. 20 years ago we didn't have check engine lights for everytime the car got a fart in sideways. It would just hickup and we'd be on our way. Now we have electronic gizmos tellling us every time it hickups and we wonder what's next. Our minds, just won't let it go even though it's usually nothing like some bad gas, a piece of carbon got stuck on a valve until it blew through, etc.
I've seen them as cheap as $23 on Amazon that says they can erase codes in the description. Do a little searching, a little reading on their functions. You'll find one for less than a shop will charge you just to plug it in and read it. However, most Auto Zones, O'Reillys, Advance Auto, etc. will read for free. Just roll in and tell them you have a check engine light and ask if they could read the code then erase it. Nothing ventured, nothing gained.
Also, If I was a betting, I'd double down on it lasting 2 years at only 5,000 miles a year. 20 years ago we didn't have check engine lights for everytime the car got a fart in sideways. It would just hickup and we'd be on our way. Now we have electronic gizmos tellling us every time it hickups and we wonder what's next. Our minds, just won't let it go even though it's usually nothing like some bad gas, a piece of carbon got stuck on a valve until it blew through, etc.
I know my concern on this one is, I found out it is a known and I guess common issue. Isn’t just bad gas or something minor that might just go away.
but I fully admit, I don’t even know what it means, and how it can hurt the car. Worse, what could happen if we are driving it.
If we can get two years out of it and then donate it, I would be good with that.
s500 GL450 GL63 Z71XL Yukon 67 396 SS velle 68 Vert Camaro 69 RSSS Vert Camaro 75 Blazer
Whoa. Yeah, they want to replace the head and not telling you what is wrong. Having that P305 code is just that the cylinder is not firing. If they did the leak down, did he say where it was leaking? He should have been able to tell you if it was leaking from the exhaust valve, intake valve, or rings. That would mean that you had some sort of failure like a valve hitting the cylinder or something that fell into the intake to cause either the exhaust valve or intake valve to be bent. This is suspicious to me.
Now that you have a reader, try to change the cylinder coil from 5 to 6 and 6 toi 5. If the code read P306, then its the coil. Doing this is a very easy job with only 2 bolts for each coil. It can also be a shorting coil wire. Start with these and see if it fixes the issue. BTW, are you noticing that its running rough? running on 7 cylinders is very noticeable.
Also, he is charging you for every little bolt that you dont need. Like the front cover bolts. I dont know why he is saying you need 16 as there are maybe onoy about 8 of them and though they are torqued, they is no real pressure being applied to them like the valve/cam cover which I agree you need new bolt for. And there also isnt 12 cam solenoid bolt either. And those bolts are very expensive.
Whoa. Yeah, they want to replace the head and not telling you what is wrong. Having that P305 code is just that the cylinder is not firing. If they did the leak down, did he say where it was leaking? He should have been able to tell you if it was leaking from the exhaust valve, intake valve, or rings. That would mean that you had some sort of failure like a valve hitting the cylinder or something that fell into the intake to cause either the exhaust valve or intake valve to be bent. This is suspicious to me.
Now that you have a reader, try to change the cylinder coil from 5 to 6 and 6 toi 5. If the code read P306, then its the coil. Doing this is a very easy job with only 2 bolts for each coil. It can also be a shorting coil wire. Start with these and see if it fixes the issue. BTW, are you noticing that its running rough? running on 7 cylinders is very noticeable.
Also, he is charging you for every little bolt that you dont need. Like the front cover bolts. I dont know why he is saying you need 16 as there are maybe onoy about 8 of them and though they are torqued, they is no real pressure being applied to them like the valve/cam cover which I agree you need new bolt for. And there also isnt 12 cam solenoid bolt either. And those bolts are very expensive.
That was the first thing I asked them to do, was to swap the coil and see if it follows or stays, then check the spark plugs. They said it wasn’t the coil and that’s when they wanted to do the tear down pressure test.
I also asked about the spark plug and I was told they checked that too.
I don’t think they have ever been replaced though. We have only had the car less than 20K miles ourselves.
It runs just fine. No noise, no stuttering, nothing seems off but the light.
I could reach back out to them and ask more questions. I did ask if they did a scope on the cylinder and he said they did and it looked fine, but from their experience this is what needs to be repaired.
I really don’t want to deal with them anymore though. That was my first time going there, and they are highly regarded.
Last edited by Squatting Hen; Feb 20, 2026 at 10:27 PM.
s500 GL450 GL63 Z71XL Yukon 67 396 SS velle 68 Vert Camaro 69 RSSS Vert Camaro 75 Blazer
Since you now have a code reader, clear the codes and see how long it takes for it to come back. You can actually drive around with the OBDII attached. and see when the pending code pops up.
Since you now have a code reader, clear the codes and see how long it takes for it to come back. You can actually drive around with the OBDII attached. and see when the pending code pops up.
okay, I will try that. I cleared the light the other day, and have maybe driven 20 miles to test and the light is still off.
s500 GL450 GL63 Z71XL Yukon 67 396 SS velle 68 Vert Camaro 69 RSSS Vert Camaro 75 Blazer
I just reread your other post where it says, "but from their experience this is what needs to be repaired". This is completely wrong. You don't fix something from their experience. You fix something from known facts like bent valves. The leak down would have told them more on what is wrong. What if it as bad rings? That would mean the motor would need to be pulled and it was not just the heads.
2004 E 500 4MATIC Wagon; 2015 ML 350 4MATIC; †2003 C 240 4MATIC Wagon (2003-2022)
Originally Posted by Squatting Hen
Guess I could try another place, just hate to toss another few hundred just to have another look.
They said they checked the spark plus, and engine coil. Then did the pressure/leak test.
They did not clear the light. It is still on.
18K just doesn’t make sense.
Based on what I am reading, I agree with everyone else who recommends getting a second opinion from a decent shop if this ever does come back. Another scenario in which I have personally observed such misfires intermittently (only on cold start...and then they go away, but the check engine light would come on) on these engines (and the M276): Failing main battery. One example (car with an M276 engine): All we did was test the battery (the original in that vehicle...which was over 7 years-old), and determined that it was near its end of life. The original misfire had happened on a very cold January day on a cold start. After replacing the main battery, the misfires never returned in all of the years since... How old is your vehicle's battery? Has it been tested?
I think you should ask yourself how much you still want to keep the car, then decide what the extra effort and cost is worth to you. I'm also all about Reduce, Recycle, Reuse. Also, compared to depreciation on a new car, spending a few hundred for a second opinion is nothing.
If you're decently handy, and have time to work on the car, I'd take care of some of the easier and inexpensive things that can help you narrow down the problem- Swap coil packs with an adjacent cylinder and see if that makes a difference or throws a code on the new cylinder. If the spark plugs haven't been done before, you could tackle that yourself and make sure the plugs are indexed correctly. While you have the plugs out, I'd pick up a cheap borescope and throw it down each cylinder to look for scoring. If that doesn't solve it, you could swap injectors with an adjacent cylinder and see if a misfire code is thrown on that cylinder. Then you could take a look at the wiring harness at the coil pack, injector, and at the ECU and look for oil intrusion that could be causing shorts; if there's oil, hopefully copious cleaning with electronics spray can fix it because replacing a harness isn't cheap either. If that doesn't work, you can try ECU replacement but that gets a bit more expensive and requires special tools; again, depends on how much you want to keep the car.
This video takes you step by step through some good troubleshooting:
severe misfires are NOTICEABLE and damage is doen by raw unburned fuel getting into Catalytic convertors and end up ruining those - $$$$
Check engine light will FLASH on/off to warn you thta cat damage is occurring and get her fixed.
IF it is occasional, you do not feel or even notice - not a real big deal and tends to be something minor.
Check engine light just comes on is steady - may not come on next time you drive.
Misfires come in 2 code types
More than one cylinder or Specific cylinder
When more than one issue tends to be before heads like intake or some sensor or computer(s) and Logic on how car determines it had a misfire.
Example I know about: On some GM trucks, Misfires determined by computer watching the alternator output therefore sometimes a bad alternator bearing or serpentine belt system can cause it to throw Check engine lights.
I am not sure how MB does it on this vehicle.
When a specific cylinder is misfiring well then it is something specific to that cylinder.
Read these links about troubleshooting a misfire; intended for novice mechanics:
also read thru the TSBs on this model/yr Vehicle.
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2014 GL 450 Cylinder 5 Replacement $18,000!!???!
