Hi,
I have a 2020 S560. Just replaced the battery at the dealership at 85k miles, after I was getting some "12V Battery Low" warnings. One day later, the check engine light comes on, and the engine rides rough. I take it to the dealer and they say the battery has nothing to do with it, and charge me $275 diagnostic fee. They say it is possibly due to bad fuel. They recommend INSTALL UPDATED IGNITION COILS & EXHAUST CLAMPS AS FIRST STEP (MISFIRE #1 CYLINDER FAULT CODE, UNABLE TO DUPLICATE CONCERN AT THIS TIME, CHECK ENGINE LIGHT NOT ON)" for $3527.
This is crazy. They check engine problem persists. It is too much of a coincidence for this to happen one day after the battery replacement.

Thoughts?

 

It does sounds like it's probably not related to the Battery replacement but take is somewhere else even an auto parts store and they will scan for codes for free (most will, advance, Oriely, auto zone etc. Once codes are noted probably best off taking it to a independent MB Repair shop and get an estimate from them. Can't really trust MB dealers especially these days. They have tried to rip me off more than a few occasions. You may more than likely just have a bad ignition coil and thats why you're running rough and check engine light, very common issue.

 

OP you are having bad luck. Coils has nothing to do with a dead battery. “Cylinder one fault code” says most likely one bad coil. The dealership is offering all coils as if they replace one; you will be back at the dealership (pissed) cuz “It is doing the same thing and you just fixed it” when another coil dies. No idea what they are referring to with ‘exhaust clamps.’ Spark plugs are a reasonable thing to do at the same time as coils. Car is five years old, Coils fail.

 

Thanks All. I will follow through on your suggestsions. It just seems very odd that I have this problem the day after the dealership replaced the battery.

 

Yes, it is odd to get that diagnosis immediately after replacing a battery. I just replaced the last of my four coil packs and the car runs fantastically well now, so the things do go bad. The other thing to watch out for is oil in the spark plug bores that these engines are prone to and which causes misfiring.

 

For half the price of the diagnostic fee, you could have gotten your own Mercedes-specific scan tool and known what codes exist. Not sure if your car requires battery registration or what, but the faults that cause the rough running will certainly be stored.

“Updated ignition coils & exhaust clamps”? Sounds like 🐂💩to me. Did they give you a printout of the diagnostic report for your $275?

 

Interesting you say this as the same thing happened to ML yesterday. I tried jumping it with a starter pack but ended up calling AAA. Then the CEL came on and it's still on, and upon starting the belts started making a very weird and consistent squeaking sound for a solid 2 minutes and then went away immediately after 2 minutes. The engine on mine (m276) has always been a little rough, but that's how it's been designed. The s560 should be much smoother obviously. Also the scummy dealer decided to replace my battery with a Diehard one when my battery had to get changed last time and I literally only found out yesterday when I tried jumping the car from under the seat. Not even sure why they have diehard in their parts department and not the OEM branded one. Haven't run the codes yet but will let you know.

 

I took the car to another place (not a dealership) that specializes in Mercedes. This is what they had to say. I am impressed by the process of elimination they followed. Mercedes just dismissed the problem after charging me a fee. Unfortunately this repair shop charged me a diagnostic fee again. They are probing some more. I hope it is not a cylinder problem.

"Technician has duplicated the concern and verified present misfire fault at cylinder #1. When allowing vehicle to run at idle and get hot, watched fault counter data of each cylinder and found misfire to climb excessively at cylinder #1. Started with a swap of the ignition coil (swapped to cylinders #5 & 6). Found the misfire to remain at cyl. #1. Swapped spark plugs around from cyl.'s 1 & 2, and again, the misfire is consistent at cylinder #1. The spark plugs were recently replaced (source: rpl. at 70K miles, per CARFAX check). Found spark plugs in OK condition and ruled out the possibility of a bad ignition coil. Technician is asking for additional diagnostic/testing time to perform the necessary testing and bore-scoping to check out cylinder #1. Technician suspects an internal engine failure being as the spark plug is dry which would otherwise be indicative of a leaking injector. If internal engine issue is verified after further checkout, it will be needed to perform a cylinder compression & leak-down test."

 

Plugged the tech’s notes into ChatGPT and got this:

Based on the diagnostics already performed and the fact that the misfire remains isolated to cylinder #1 despite ignition component swaps, here are the most likely possible causes, grouped logically by system. This also supports the technician’s request for additional diagnostic time.

Ruled Out / Less Likely

• Ignition coil failure – Coil swapped to other cylinders with no change.
  
• Spark plug failure – Plug swapped; condition OK; misfire stayed at #1.
  
• Basic ignition control issue – Misfire is cylinder-specific, not random.
  

Most Likely Remaining Causes

1. Mechanical / Internal Engine Issue (High Probability)

Given:

• Misfire worsens at hot idle
  
• Dry spark plug (no fuel fouling)
  
• Persistent misfire on the same cylinder
  

Possible internal faults include:

• Low compression at cylinder #1
  
• Burnt, bent, or sticking intake or exhaust valve
  
• Worn or damaged piston rings
  
• Cylinder wall scoring
  
• Head gasket failure (localized to cyl. #1)
  

➡️ Compression and leak-down testing are essential next steps to confirm.

2. Fuel Injector Issue (Moderate Probability)

Even though the spark plug is dry:

• Injector may be electrically failing (intermittent or heat-related)
  
• Injector may be clogged or restricted
  
• Injector driver circuit issue (wiring, PCM output)
  

Recommended tests:

• Injector balance test
  
• Injector resistance test
  
• Swap injector #1 with another cylinder (if accessible)
  
• Verify injector pulse with a noid light or scope
  

3. Valve Train or Timing Issue (Moderate–High Probability)

Especially if bore-scoping is planned:

• Valve not seating properly
  
• Carbon buildup on valve face
  
• Cam lobe wear affecting valve lift
  
• Hydraulic lifter collapse (if equipped)
  

Bore scope inspection can reveal:

• Valve damage
  
• Piston crown damage
  
• Excessive carbon or oil intrusion
  

4. Vacuum or Intake Leak (Lower Probability)

• Intake runner leak near cylinder #1
  
• Failed intake gasket
  
• Cracked intake manifold
  

Would typically cause a lean misfire that worsens at idle.

5. ECM / Wiring Issue (Lower Probability)

• Faulty injector control circuit for cylinder #1
  
• Pin fitment or wiring damage
  
• Rare PCM failure
  

Usually considered after mechanical and fuel tests pass.

Recommended Diagnostic Path (Justification for More Time)

1. Compression test (hot and cold)
   
2. Cylinder leak-down test
   
3. Bore scope inspection
   
4. Injector electrical and flow testing
   
5. Vacuum leak smoke test (if needed)
   

Summary

The evidence strongly points toward a mechanical failure within cylinder #1, with fuel delivery issues still possible but less likely given the dry spark plug. Additional diagnostic time is reasonable and necessary to prevent unnecessary parts replacement and to confirm whether internal engine repair is required.

If you want, I can also:

• Help you write this up as a warranty claim justification
  
• Translate it into customer-friendly language
  
• Rank repair cost risk scenarios based on test outcomes
  

 

The dealership at this point are really rip-off artists. I had AC Failure and since I had aftermarket warranty I took to dealership, who charge way more than the insurance would pay ($275 vs. $329). It was an oddessy and the first dealer (AC failed 500 miles from my house in 95 degree heat) decided a needed a new batter which didn't do anything. I ended up with the battery for free as I told them I wasn't interested in their $650 battery. Second dealers back home identified motor mount failure, leaking value covers and belts. The insurance did actually replace the AC and motor mounts (wow I can't tell the difference, but motor mounts at 9 years and 47k, my Nissans needed those after 25 year and 150k). They said that the value covers were not leaking and told the dealership to wipe it down and call it a day.

Moral of the story is that you cannot trust a dealership. They also suggested replacement of the brake pads when my trusted Indy mechanic told me they had 50% of pad left. For future service I need to find a dealership that charges closer to $275 or use my indy to solve problems. Bottom line, doing stuff like battery at dealership is VERY expensive and they also find other things that are 50/50 you do not need.

 

I agree about dealers. I really thought I could trust mb of Clearwater but was told by them when I was in for a brake flush and a cabin filter a few weeks ago that I needed all four mbc hydraulic struts replaced. The Struts are fine. They quoted over 16000 to do the job without even any talk of changing the hydraulic fluid. They said the struts were 4000 dollars each. I could by aftermarket ones for around 400 dollars each. Criminals.

 

Did we say changing a battery was expensive, a rip off? Yup. https://mbworld.org/forums/gle-class...t-rip-off.html

 

Not just Mercedes dealers...

 

Ah the classic stealerships.

 

I took the car back to the dealer. Their initial $275 fee said "no trouble found". After I showed them the rigorous process of the third party mechanic, they now agree that there is an engine failure. Service rep says it is very unusual and he has never seen that before in a Mercedes engine. My question is - how much responsibility should Mercedes take? The car is not under warranty any more but a core engineering or production failure on a $150k car should have some accountability - with vaunted German engineering. It is a 2020 S560, which I fully expected to drive for another five years. And now I am facing the prospect of another huge expense with perhaps no trade-in or resale value for my car.

 

THIS. My X7 started making some suspension sound around 30k miles and it was a couple months out of warranty. The issue was the control arms leaking fluid, but the dealer decided to quote a $23k quote including control arms, all 4 air bags/shocks, tires, and something else. Let alone this car barely had 30k miles.

 

Did the independent mechanic scope the cylinder and perform compression test yet? If so, what did they find?
As far as the dealer; at minimum they should refund your diagnostic fee since they didn't find the problem. Since the fault happens after the car warms up they had time in their one-hour diag fee time. But as far as warrantying the engine, probably no luck at this point. How long have you had the car and who else has worked on it? If you find that cylinder #1 has a problem, it will be interesting to find out what caused it. But you wwon't know anything without scoping the cylinder.

 

I am not tech-savvy in this regard. THe car has been dealer-serviced in since I bought it five and a half years ago.
This is what the third-party mechanic said -Performed borescope of cylinder #1 and could not really

find concerning enough damage to the cylinder walls that would cause a misfire. Minimal wear and scoring is found which is normal given the age/miles on the

engine. Performed cylinder compression testing at cyl.'s 1 & 2, found compression at cylinder #1 lower than specified (90psi.). Performed check of cylinder #2 to

compare results, which is testing much higher (135psi.) Checked cylinder bore once again to examine the valvetrain as best as possible, particularly the valve

seats for defect. At this time, technician cannot fault a particular (visible) failure with scope. Given the low compression result at cylinder #1, technician is highly

convinced of an internal engine issue but in certain instances like this, tearing down an engine to the point of failure would be the next advised step pending one

more further test of cylinder leak-down.

 

Sorry you are going through this. Something very similar happened to me with BMW and spoiled me on the brand and company...had to scrap a beautifully maintained car at a point in life when I could not afford it...would up in amg land

Unfortunately dealership serviced means this car was under serviced from the start...at least for the way I drive or maintain cars.

Did they do a leak down test? I would have first suspected an electronic issue but the compression test is pointing elsewhere. They could even do a gas test of the coolant to rule out head gasket.

Unfortunately the dealer is still not your best bet and it's unlikely at your mileage that you will get a goodwill repair. Best case through a dealer is that they get you into a newer car for little cost.

You really need to really trust your mechanic and find someone with experience with these types of engines. Get it to the best indy around that works deep into engines if you plan on keeping it. Could it be a stuck valve? Could it be much worse.? The cost of the repair will outweigh the move to a new vehicle. If you cant get a perfect diagnosis, youre looking at 20k plus (not them repairing it, but you going to an indy) imo by the time they figure anything out and be prepared for them to offer you an engine for a cool 60k plus.

Any very high dollar engine can be a gamble to own without a warranty so consider extending them if you dont work on the car yourself.

Do you have any pics to share from the scoping. We can help...

 

It seems that a cylinder leak-down test is indicated at this point. Please let us know if that was done. If the intake or exhaust valves do not seal properly, compression can obviously escape from the cylinder. This can occur due to wear, overheating, excessive carbon build-up, or damage to the valve seats. I think the leak-down test would help determine if the car is worth saving. Although worn or damaged piston rings, a blown head gasket, or a cracked cylinder head or block are possibilities, I think the cylinder leak-down test will significantly narrow down the issue. Sorry you are not able to find a knowledgeable Mercedes mechanic in your area.

 

This is a wild guess, but maybe the injector seal has broken down and you are losing compression there. I would think, however, that would be easy to detect. I would look for discoloration or other signs around the fuel injector.