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Hi lads, after months of dread I hope some of you can help me, have any of you had the issue where your car cuts off boost sharply after 5k rpm? In all gears. Boost ofc returns in the next gear, only too cut sharply after 5000 rpm again.
No error codes, no warnings, even with Xentry apparently. C63S S205, 2015. My car is fully stock and never been tuned. TC is fully off, both in "M" "D" or the "semimanual", tried to "reset" the TCU with the whole holding the throttle pedal procedure, even tried disabling every assist in Dynomode.
After multiple attempts from my local AMG specialist, the issue still persists... At a point where I am pulling my hair out over this issue. He says I should try taking it to a tuner, as he doesn't know where start and end and doesn't want to keep charging me for hours without a final fix.
Upon my request local AMG specialist have changed all vacuum hoses going to the turbos including crank case ventilation lines. And a "vacuum/pressure transducer valve". Everything has been changed except the left tank purge valve. The reasoning for changing the vacuum lines is a service bulletin (https://static.nhtsa.gov/odi/tsbs/2019/MC-10166704-9999.pdf) where they are prone to collapsing after some aging, and this would apparently cause the wastegates to open prematurely. I have also made sure the new vacuum lines are not too soft/collapsing.
The following specific parts that are relevant for my car have been changed:A1770103500 (left purge line)
A1770103006 (crank case purge line)
A1771402364 (vacuum line)
A1771400000 (vacuum line, goes directly to wastegate actuator, was the prime suspect before, in the 'symptom' youtube video below, this line fixed issue for him)
A0001531800 (vacuum/pressure transducer)
Parts not yet changed according to bulletin (tank purge valves): A0014700993, i have these on order, and it look straight forward. But i am afraid this is the least likely part to fix the issue as it has nothing to do with the waste gate actuation (correct me if I am wrong here)
How it is now: This is the exact symptom I still have (cuts boost in any gear after 5k rpm):
(don't mind the stage 2 performance increase, but notice there is boost all the way up the rev range until the gear change, i could not find a better video that shows a full pull with the boost gauge visible, please if you have such a video, please send it to me)
Any help is dearly appreciated, as it's nearing pandemonium. We all love our cars I guess, and want them to just run right.
Hi Jack, yes it's "old" haha, S205 wagon, supposedly this issue was addressed 2017 and onwards, but that's when the cars got OPF (sadly, we can't win all the time). I think the "model year" is 2016 but it was registered in 2015, so the first batch of cars out of affalterbach basically.
Mine does it exactly after 5000rpm, more or less same thing on the video but it's hard to see due to the angle, guess this symptom might not occur exactly at the same rpm for all cars if it's got something to with finicky vacuum. Anyways, cuts boost sharply, if don't shift it rides the gear all way out and feels very out of breath (since no boost).
First your AMG guy is a funny man if he had changed all this things without a fail ? and tells you go to tuning guy now.
Xentry does read codes AND can testing !
If you use it you should know how it works etc.
the symptomes are :
- at 5000 no boost
- at 5000 no boost untill revlimiter
- same problem in all gears
- boost cuts prompt
right ?
first do some new Xentry testing ( local MB dealer)
maybe update all modules on car.
i can not believe there is nothing.
second i would do make vakuum hoses from turbo new with OEM hose. ( they are old now)
check the vacuum can on turbos - you need WIS with the values too. vacuum testing an mechanic testing
check the 2 Blow Off Valves or Recirculation Valve ( same thing other words) - front of engine.
look turbosmart.com they have a installiation video for C63.
if i would do all this i woud think 50/50 change to catch the problem.
what means : … but that's when the cars got OPF ?
Last edited by C63s_Jack; Apr 5, 2026 at 02:26 PM.
Hi Jack thanks for the reply, but I think there is a misunderstanding, "second i would do make vakuum hoses from turbo new with OEM hose. ( they are old now)", all vacuum hoses to the turbos have been replaced with OEM new ones. And they hold vacuum and do not collapse.
I do not have an Xentry tester myself, so yes I can try the local MB dealer.
"check the vacuum can on turbos - you need WIS with the values too. vacuum testing an mechanic testing" - I am not sure I understand this, but the AMG workshop I took the car to, claim expected versus real values when using Mercedes software for testing were correctly matches. Which I do not understand at all.
I will definitely check the blow off valves, what should I look for? and what you do think about replacing the fuel tank purge valves? (the ones that can click)
OPF is basically particle filter for petrol cars, like particle filters for diesel cars. We got those mandatory in europe now.
I do not have an Xentry tester myself, so yes I can try the local MB dealer.
"check the vacuum can on turbos - you need WIS with the values too. vacuum testing an mechanic testing" - I am not sure I understand this, but the AMG workshop I took the car to, claim expected versus real values when using Mercedes software for testing were correctly matches. Which I do not understand at all.
… blow off valves, what should I look for? and what you do think about replacing the fuel tank purge valves? (the ones that can click)
OPF is basically particle filter for petrol cars, like particle filters for diesel cars. We got those mandatory in europe now.
Xentry & use it with full force you need a briefing.
Thats not a simple app.
testing the vacuum cans on turbos is no xentry job.
they are mechanical. there us no wire & electronic.
blow of valves testing is a good question.
if we would have WIS we could look.
i think you can test with Xentry too because they have a wire.
click click valves - yes if they worn make them new but dont buy ling lang sh*it from china. buy oem.
this hard stop at 5000 …. that is a speacial thing.
i am not so versed with M177 in deep detail.
what happend with usa … 2015 OPF ?
i am wondering. sounds you overtake green Europe
Last edited by C63s_Jack; Apr 5, 2026 at 04:49 PM.
"testing the vacuum cans on turbos is no xentry job. they are mechanical. there us no wire & electronic." - they specifically told me that they manual pumped down the hoses and checked for holding vacuum and they did not collapse. I doublechecked this by shortly replacing the soft vacuum hoses from the "turbo cans" to the hard vacuum with some even hard rubber hoses, changed nothing. I think we can cross off collapsing vacuum lines.
But, i was also worried about maybe some leak in the intercooler???, I asked for a smoke test, but they did not want to do this after, why I don't know! I don't know how to do this myself. They simply said the intercooler system is tight and leak free! (hmmmm)
"click click valves" I bought the ones from Bosch, the OEM maker of the fuel tank purge valves. I just hear them clicking a bit, but I don't how to check if they are worn
I will try to update you regarding blow off valves and definitely the fuel purge valves, and MB dealer diagnostic (if they can do anything, the MB dealer quoted me 600USD for a "full test" and 400USD PER HOUR of work, exorbitant fantasy prices! Danish MB dealers are criminal at this point).
In the meantime, let's hope someone else can chime in and give hint or solution to this very specific M177 problem, can you tag someone in here???
the vacuum cans on turbos have a membrane and the struts should go easy.
the click click valves i dont know that they can do such a problem. but if they gone loud make new.
400 US per hour - crazy price .
i hope for that money only specialist do job on car.
to save money you can ask e.g. the turbosmart guys too, ask question about the two blow of valves. you can put new from them on engine ( they have a this valves with cable like oem and a good DIY video) . i think that is cheaper as MB do this job.
all that things we have talked now i am not sure that this can cause such a 5000 rpm problem . but its easy to check this things.
This abrupt interruption of the boost is a particular problem. normal acceralation and then nothing - something must stop boost.
i guess that has nothing to do with old leaking rubber hoses etc.
how much miles have your car ?
fuelpump / filter okay ?
if car is in P/N is it the same ?
this problem was it from on to other day there ?
Last edited by C63s_Jack; Apr 6, 2026 at 02:45 AM.
@perkpal If boost is working fine at all other times except after 5000 RPM, I think something could be triggering the electronic bypass valves to open.
A physical boost leak in the system (cracked intercooler / cracked hose /cracked intake manifold, etc...) would likely be persistent at any RPM. But, if you can see full boost at 2000 to 4000 RPM then it's not a leaking hose, or a crack in the plastic intake manifolds because those would leak whenever the boost was at full pressure regardless of engine RPM.
The fact that it cuts sharply at 5000 rpm tells me something is releasing boost pressure, that was there, and holding, at any rpm less than 5000... So the question is what engine operating condition is signaling the bypass valves to dump boost (if my theory is right and that's what is going on). If you can get a tuner or mechanic to ride in the car with you and live monitor the actual values (datalogging) of the bypass valves they might be able to spot exactly when / if they open and what engine values are present when it occurs (freeze frame snapshot of the datalog).
The data log may show that perhaps it is a fueling issue, such as a failing high pressure or low pressure fuel pump, or injector, and the car is cutting boost because it detects it can't supply enough fuel beyond 5000 rpm. (I would think this would trigger a check engine light or a stored code of some kind though) . Again, live monitoring the engine values using Xentry is the way to see if fuel pressure is dropping off or injector duty cycle is maxing out, or bypass valves are opening, etc... at 5000 rpm and beyond.
A competent tuner may be much cheaper than a mechanic or dealer to do this, and a real tuner should have a dynomometer they can put the car on so you don't have to do this on a road test.
Hi Jack, this is MB dealer garage prices here (criminal haha)... the local third party AMG specialist is about 100usd/hr, they do very good service. This problem is just something they really don't want on their hands apparently, bad luck for me.
how much miles have your car ? = 79.000km, bought at 44.000km 3 years ago. fuelpump / filter okay ? = i don't believe fuel pump/filter assembly have been changed yet, but maybe it should after 10 years? If i remember correctly, that's the recommended period.
if car is in P/N is it the same ? what do you mean? car does not allow to build boost in P/N this problem was it from on to other day there ? I first noticed this problem in october, the first 2 years car was perfect. It gets regular service every year and things are changed preventatively, just new air filter, spark plugs, oil, oil filter, lower control arms etc. etc. I keep up with the recommended schedule from MB dealer (even if it's too much sometimes)
@perkpal If boost is working fine at all other times except after 5000 RPM, I think something could be triggering the electronic bypass valves to open.
A physical boost leak in the system (cracked intercooler / cracked hose /cracked intake manifold, etc...) would likely be persistent at any RPM. But, if you can see full boost at 2000 to 4000 RPM then it's not a leaking hose, or a crack in the plastic intake manifolds because those would leak whenever the boost was at full pressure regardless of engine RPM.
The fact that it cuts sharply at 5000 rpm tells me something is releasing boost pressure, that was there, and holding, at any rpm less than 5000... So the question is what engine operating condition is signaling the bypass valves to dump boost (if my theory is right and that's what is going on). If you can get a tuner or mechanic to ride in the car with you and live monitor the actual values (datalogging) of the bypass valves they might be able to spot exactly when / if they open and what engine values are present when it occurs (freeze frame snapshot of the datalog).
The data log may show that perhaps it is a fueling issue, such as a failing high pressure or low pressure fuel pump, or injector, and the car is cutting boost because it detects it can't supply enough fuel beyond 5000 rpm. (I would think this would trigger a check engine light or a stored code of some kind though) . Again, live monitoring the engine values using Xentry is the way to see if fuel pressure is dropping off or injector duty cycle is maxing out, or bypass valves are opening, etc... at 5000 rpm and beyond.
A competent tuner may be much cheaper than a mechanic or dealer to do this, and a real tuner should have a dynomometer they can put the car on so you don't have to do this on a road test.
Hi Roy, thanks for your input and pointing these things out, I was also in this line of thinking, as the event itself could be logged, I will definitely try to convince a good tuner to do this with me on a drive. I tried to convince my local AMG specialist with Xentry, but he was not up for it as he claims ALL faults would be stored anyway and he would be able to see them in Xentry, so I gave up on that. Can't force the guy, maybe he is tired of my car and its problem...
One more thing to mention, the power gauge inside the car itself, I can only get that to show around 275kw max or around 330hp. So something is definitely off there, people also mention soft limp mode that throw no codes, is this a possibility??? and would it be smart to do the AWE exhaust valve simulator mod? Thinking back and remembering, The very first time this year I took it to my local AMG specialist, he mentioned an exhaust flap error code was stored and it was removed and they did not get it again when they test drove the car. I don't have a tester myself so I don't know what to think, I am trying to order a generic OBD2 tester myself right now.
One more thing, recently I just took the car for a short test drive to provoke the boost cutoff, and did it all times, except for one single instance. In comfort mode, exhaust open, in "D" driving around 60km/h if I fully floor the throttle the boost continues all the way to 6000rpm (then I had to let off, due to traffic safety). But on the highway driving in any mode, any gearbox mode, any exhaust mode driving around 100km/h (in 7th gear) and then fully flooring the throttle, the car downshift to 3rd gear and cuts off boost immediately at 5000rpm.
@perkpal okay... Now we are getting somewhere. Yes, stuck, or non-functioning exhaust pipe valves are one of the things that can cause the car to go into soft limp mode (no check engine light will display, and the code would only be in Xentry... Many aftermarket scanners won't see / read the "soft codes") . Particularly, the third valve in the H-pipe section near the transmission. (Many people just check the two valves in the rear st the mufflers) I suppose one way you could test it is to plug an AWE simulator into the third valve plug and see if the problem goes away. If that does it, the actuator motor is kind of expensive from MB, and somewhere on this forum is a post of the Ford part number for the same actuator, but much cheaper. If changing that actuator, then make sure to check the physical valve rotates freely in the exhaust pipe. There are several other possible causes for that soft limp mode / power limited mode, just do a little searching on this forum and I'm sure you can get some ideas.
Hi Jack, this is MB dealer garage prices here (criminal haha)... the local third party AMG specialist is about 100usd/hr, they do very good service. This problem is just something they really don't want on their hands apparently, bad luck for me.
fuelpump / filter okay ? = i don't believe fuel pump/filter assembly have been changed yet, but maybe it should after 10 years? If i remember correctly, that's the recommended period.
if car is in P/N is it the same ? what do you mean? car does not allow to build boost in P/N
Your AMG specialist - it sounds like AMG service specialist. But with such problems you need AMG problem spezialist. 100$ is a good price and its okay that he told you he must stop doing.
thats a good solution that he offers this - other spezialists repairing and repairing till car is down and coustumer broke.
the fuel filter has a long service distance , i dont know exactly but i heard that complete fuel pumpe must come new - expensive thing.
i think if it is clogged there is not such a sharply rev stop.
the thing with the flaps sound realy interesting - thats a hot track what can cause the problem like it is in my mind. i know from exhaust valve problems but i dont know is cause rusty mechanic or e-motor ?
the next is the error code is he made by e-motor or is there a pressure sensor how check the exhaustsystem / exaust pressure ?
i know that all 3 are driven by a e-motor. U78
no rev / build boost in N/P is this a special US feature ?
if you ask the turbosmart guys for that valves front engine ask them how are the symptoms of faulty valves .
i think xentry shows them too.
what is a AWE simulator ?
Last edited by C63s_Jack; Apr 6, 2026 at 03:12 PM.
Hi again Jack & Roy, I will try to make sure the exhaust code is not back and the car is not soft limp mode (I am not sure what this soft limp mode code looks like in xentry, so please let me know what it is exactly in xentry, i could not find specific code for this online). For that I think I have to go to a good tuner with Xentry, and try to ask him to remove these code and maybe code the valves to permanently stay open?
Until then, if you or any other guys come up with a good idea or ANY idea, please let me know. Because I am very quickly running out of ideas. My local AMG specialist is a good guy, I trust him. But I don't think he wants this problem on his hands, I don't blame him (maybe he thinks the time & risk is not worth it), so I have to go somewhere else to get this fixed...
I have a little more hope talking to you guys, at the end of the day. It's just a car, not magic. A man built it, and a man can fix it. How is the big question...
I have a little more hope talking to you guys, at the end of the day. It's just a car, not magic. A man built it, and a man can fix it. How is the big question...
Thats a good mindset !
Tackle M177 problems by the *****.
Soft limp mode - i dont know what this means.
no warning light in combi but error code in Xentry ???
Hi guys, today I changed the fuel tank purge valves. It went easy, no errors on the dash after change, good job, BUT unfortunately it changed nothing in the behaviour of the car. In a few days I will go to a tuner with Xentry who live scan while I drive it. So let's see. Is there anyway I can check physically to know if one of the exhaust flap actuators is dead? Does the exhaust open completely when the car is off? Today in comfort mode if I am cruising at under 60km/h, and then full throttle I can get the boost to continue to around 6000rpm before the sharp cut off where the car feels out of breath.
this guy shows an exhaust valve problem with the amg gt63s, same m177 engine, but I don't know if the valve actuator or the behaviour is the same??? Is it easy to replace this valve actuator? All your answers are appreciated.
It would be hard to see if the center (third) exhaust valve is working while the car is stationary. It's easy to change out though... It's just 3 little bolts. Here's one I took off mine a while ago... It's missing a little coiled spring on the motor, but hopefully you get the idea.
Just had a similar experience with my 22 GLS 450. I checked the boost solenoid and actuator and found they were a bit dirty, so I cleaned them out and re-checked the boost pressure, everything's good now.
It would be hard to see if the center (third) exhaust valve is working while the car is stationary. It's easy to change out though... It's just 3 little bolts. Here's one I took off mine a while ago... It's missing a little coiled spring on the motor, but hopefully you get the idea.
Here you can see the oem exaust actuator inside … i think the housings are plastic welded ?
Here's the Ford version... Exact same part, less expensive, and is made by the same company (Kuster). Peel your sticker off your AMG one, and put it on the Ford one, if it makes you feel better.
Hi guys, small but significant update from me, went and got an XENTRY report before clearing codes, and one after clearing codes + test driveThe pre-clear scan showed the following stored faults, most of which I believe were triggered by (a low coolant event, I hadn't mentioned this but it's makes sense now that I see the codes), and most are also gone now:
P026E71 — Intercooler coolant pump actuator blocked (6 occurrences, up to 92 km/h), see below
P026E7A — Intercooler coolant pump, leak or defective seal (3 occurrences), see below
P25567B — Coolant level sensor too low (1 occurrence at 78,640 km), see below
P048000 — Electric cooling fan output fault (1 occurrence), see below
P002477 — Exhaust camshaft position bank 2 deviation (13 occurrences, stored), odd
P141300 — Exhaust flap 2 short circuit to ground (active)
P13C900 — Exhaust flap short circuit to ground (active)
B181E64 — Hood sensor implausible signal (2 occurrences) me messing around and maybe moving the car in the parking lot with the hoodlatch open or just when I replaced the fuel tank purge valves with the hood open
C159916 — Tyre pressure sensor battery fault (active + stored), need to fix this ofc
B1FE097 — Gear position display malfunction (stored), odd
Looking at the Xentry report and matching the km-stamp of errors with my km-stamp on the bill after the vacuum hose change, I discovered this!!! So I collected the car at 78,636 km. Within the first 4 km a coolant level warning triggered, and intercooler pump faults followed within the first 20–30 km. The intercooler coolant reservoir had clearly not been refilled after reassembly. On this single 25km high way drive from the workshop (with 5-10 short kickdowns in the beginning) the gearbox temperature climbed to approximately 130°C!!! with the cooling fan running flat out. I backed off immediately once I discovered 120°C+ (stupid and distracted, was focused on the boost behaviour, even though the temp is right under it) and kept the rest of the drive home gentle. The missing refill, I consider it an honest mistake from the workshop but it's worth documenting. I got the coolant refilled and no overheating gearbox returned. And no more coolant/intercooler errors (I just could not see those).
we went for a 20-30 min test drive with many kick downs. Almost everything cleared and stayed gone. The only two codes that survived both the clear and the test drive are P141300 and P13C900 — exhaust flap actuator short circuits to ground on the M177.
This service bulletin (https://static.nhtsa.gov/odi/tsbs/20...58275-9999.pdf) says to only repair the wiring if the actuators are shorting to ground, not to necessarily replace them, what do you guys think??? I was under the car today, but not reach and disconnect the plugs for the actuators to try to clean them. It was dark out, should I just unscrew the entire actuator and check it or just ask the workshop to do it? What do you think about the whole camshaft sensor errors?
The tuner mentioned it would be a good idea to get a software calibration of the throttle position sensor as it was also off during the test drive, does that make sense? or is it just the exhaust flaps that hinder the throttle from being fully open??? He said it seem like a variable valvetrain module change (the gears that varies valve timing), which he even offered to do..., isn't that a bit overkill already considering the mileage and just the exhaust valve flap error being sticky after the test drive???
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Sharp boost cut after 5000rpm
