Hello guys,
I’ve been having issues with my car (Mercedes-Benz C350 Coupe 4Matic M276 3.5L engine 106,000 miles). Even took it to a dealer and the head mechanic took it for a test drive and told me that he wasn’t able to replicate the issues and that it drives normal. He also told me that he could inspect it but I would just be wasting my money because they bill $210 an hour and he wasn’t able to replicate the issue so they may never find it.
My car does have issues. And a lot. Could be stemming from one thing could be not.
Issues are the following:
-Car jerks/kick when I press the gas pedal why cruising.
-Car sometimes changes gears smoothly, sometimes more rough, and sometimes extremely rough.
-If you press the gas suddenly on the highway, you feel a thud in the car, a jerk, then a bit of hesitation, then the power comes all at once.
-Going uphill, while maintaining the same throttle position, RPM’s decrease sharply, like it’s loosing power, then downshifts roughly.
-Rapid knocking sound when at idle inside the cabin. No knocking sound in engine bay. Traced the sound to the rear seats, which could he or could be not pointing towards the fuel tank/pump.
-Sometimes it hesitates when accelerating sometimes it doesn’t.
-Hissing sound in engine bay (could be one of the pulleys).
-Sometimes the car idles like a tractor (sound). When I start moving this idle sound goes away. Sometimes it goes away without moving but then it comes back.
-Body shakes when accelerating//cruising. Subtle shake but it’s there.
What was done on the car:
-Transmission fluid changed under previous owner 32,000 miles ago.
-Oil changed 3,000 miles ago using Mobil 1 European formula 0W-40. I change my oil every 3.5-4k miles out of precaution. With oil filter of course (Mann of Purflux).
-Control arms changed (Febi).
-Lemforder transmission mount.
-CV axles (Not OEM).
-HELLA fuel pump.
-Transfer case fluid changed.
-Brake fluid change.
Codes:
-P2540: Low Pressure Fuel System Sensor Circuit Range /Performance

I’ve been trying to keep the car in top shape. Never ignored anything. Got a low pressure fuel code so I swapped the fuel pump. Code changed from fuel pressure too low in low pressure system to the code above. Put in a Hella fuel pump because apparently they’re reputable and they’re the same company as Pierburg. It could be faulty tho given the sounds. CV axles are not OEM so they could be not %100.
The problem is none of the mechanics I took diagnosed anything. They always seem in a rush and that they’re doing me a favor although I’m paying a good amount of money. They always have so something better to do so they don’t properly diagnose anything. I don’t know what these symptoms could point to. I’ve been getting conflicting answers online. I just need someone to help. I’m on the verge of giving up on this thing.
Ah also the head mechanic at the dealer told me that this car is very sensitive so any problem with the engine or transmission and it’ll give me a check engine light. I don’t have a CEL but I do have a code stored which I mentioned above. This head mechanic told me that all W204’s have this code and I should just ignore it because it’s normal apparently.
Could it be the transmission? Could it be the engine? Fuel pump? CV axle? Anything major? Minor? I don’t know. I need some help.
Thank you!

Can you replicate the problem? Did the mechanic take it for a test drive without you in the car?

You know you have two fuel pumps, right? The high pressure fuel pump (HPFP) is driven by the bank 1 (right side) cam shaft. It can get noisy when worn or failing. That could coincide with the P2540 code. And no, not all W204s have that code. That's a BS answer when they are not interested in fixing your problem. Also, not all serious problems will throw a CEL if they don't affect emissions.

When did these problems start?

What scan tool do you use to read codes?

Thank you for your response.Yes I do but I don’t have any codes related to the HPFP. The previous codes and the current codes point to the low pressure fuel system. The current code points to the LFP Sensor circuit. I don’t know to be honest could it be the HPFP?
Could it become noisy because it’s receiving low fuel pressure from the LPFP? Because there’s rapid knocking coming from the fuel tank that’s behind the drivers seat. Also, I used a iCarSoft to pull the codes.
They started a couple of months back. It wasn’t as severe before. Also sometimes it’s almost none existent and sometimes it’s strongly present. I’ve been on endless trips to the mechanics. As I said none of them had the time to diagnose the issue properly. I was fed up and took it to a dealer to have him say what I quoted above.
Thank you!
Edit: I attached a video of the engine bay sound. As I described before, it comes when idling at D, then is gone at N or P. And that’s what happened in the attached video. Sometimes, it goes away while still at D.
Wasn’t able to upload it here so there’s the link: https://imgur.com/a/Wb946FO?s=sms

Is that direct injection? From searching around I hear that is normal to sound like that.

heres a discussion about it: https://mbworld.org/forums/glc-class...ds-diesel.html

Hello,
Yes it is DI, but the sound is sometimes significantly louder. Sometimes when it’s on D the sound quiets on its own and sometimes it’s loud.

Good day

I once had similar problems with my CLK550. Car jerked at low speeds especially in parking lots. On the open roads it is a rocket. Three different mechanics including one dealer were all lost. They made me pay for an intake manifold, no joy. Then ECU, no joy. Then throttle pedal, I said no. I suggested the ignition switch, They ignored it and kept fumbling with other stuff. Made no difference at all. They eventually changed the ignition switch, problem solved. Two years now.

But I am not suggesting it is your problem, and your car is a diesel. I am no mechanic. It could also be something stupid. These "wise guys" I dealt with always over analyse and coin it all the way. Rather make sure.

I picked up this thread. Check on it, https://p2540.enginetroublecode.com/...s-benz-c-class, or . Symptoms are very similar. Maybe check the catalytic converter, oxygen sensors. I don't know what the suction control valve (or similar) is like, once had a similar symptom with it on my diesel LDV.

No, the C350 is gasoline direct injection (GDI or DI). Still, your comments are worth exploring.

Okay, sorry. Makes it a bit easier. Diesels can be very complicated. Hope it helps somewhat. Hope it's not the ECU. Good luck. Keep us posted please,

I just noticed the transfer case fluid was changed? I thought the transfer case was part of the transmission? I know there's a separate fill plug but didn't know there's also a drain.

The first 4 issues you list could all be related. I wonder if its fuel related, low fuel pressure causing the hesitation. *I actually just noticed you have a code P2540, I was typing as I was reading. My W204 has a different fuel system so not really knowledgeable on yours, but here is an interesting thread I was just reading on M276 with the P025400 code. Someone had code P008700 and replaced the fuel filter then they got the P25400 They mention using Hella brand at first and then switching to Mercedes fuel pump and filter and solved the issue (post# 50). https://mbworld.org/forums/e-class-w...ine-light.html

I dont think its HPFP related, appears that code is with the low pressure system. Can you check the low fuel pressure with your scanner, at idle then WOT?

Rapid knocking sound at idle. Jack up the rear and try to see if you can locate it under the car and/or remove the rear seat and see if you can pin point it. From the thread I linked to above it may be the fuel pump?

Body shaking while accelerating. Im trying to imagine what that is, do you feel it in the seat or in the steering wheel? My car felt like it was shaking/bouncing down the road where i thought I had something wrong, I then replaced the tires since the old ones were cracking everywhere and the issue went away and it rides perfect now.

I will say if i had a mechanic tell me to just ignore a code I would lose confidence in them and find someone else to work on the car. Then again I don't really have confidence on anyone working on my car from past experience. Recently had my tires replaced and the shop broke two center caps and glued them in without even telling me about it, thats shady and dishonest to me.

Hello,
I actually had codes P008A and U0427. I swapped the fuel pump with a Hella one and I got the P25400 code. So I think the issue is pretty similar. The first 2 codes were read with a BlueDriver before I changed the fuel pump and the last code was with an iCarSoft after I changed the fuel pump. Bought the Hella fuel pump because I thought it was a good brand. I’ll just swap it out then. Do you recommend OE (Pierburg) or Mercedes fuel pump? Considering the Mercedes one is 3 times more expensive.
Also as for the vibration. it’s the seat and the body of the car. Also it’s more noticeable at low speeds. My wheels are surly bent, since they’re the notorious AMG mags and I live in a city plagued with potholes. Also it’s 12 years old so it’s had its fair share of potholes. No problem with the suspension though, all control arms have been replaced and struts are still fine. I’m either suspecting CV axles (since it’s at low speeds) or wheels maybe?
Also that’s my exact problem. I’ve tried and met so much incompetent mechanics that I don’t trust anyone anymore. Most of them are there to make money and that’s it. They don’t properly diagnose anything. Thought going to the dealership would yield different results but I was very wrong.
Thank you!
Edit: Ok I just noticed that you said that the transfer case was a part of the transmission. Took it in for a leak and the mechanic said that the transfer case was leaking due to the CV axle moving around and vibrating. He apparently refilled the transfer case with ATF fluid (took about 1 litre) and replaced the CV. I’m guessing the mechanic was lying? Was done maybe a month ago.

Maybe he meant the front differential was leaking and filled it. The cv axle goes into the differential. the differential should be filled with gear oil, like 75w90 I believe.

Is the Mercedes fuel pump made by Pierburg? I thought it may be Delphi, but if it is labeled Pierburg I would feel comfortable getting that one.

I’m certain that he said transfer case. He called the dealership infront of me to ask the type of oil that goes in there and they told him the blue ATF. I kept a close eye on it for the past month and it’s bone dry, no leak at all. I just need to know because I guess most of scenarios are negative;
-Differential was leaking, stopped because he swapped the cv, and now it’s low on fluid.
-Transmission is now overfilled.
- Mechanic scammed me and just swapped the cv.
He billed me $600 for a transfer case fluid refill (1 litre), CV axle (left), and a transmission mount.
This just keeps on getting worse and worse lol.
As for the fuel pump, as far as I know the OE one is Pierburg not Delphi.
Thank you for your help!

Hello, im experiencing similar symptoms, did you fix the issue?