Hello all,
I have a belt chirp that I couldn't fix yet but during the progress I realized it is multiple parts together starting with one and killing others becoming difficult to solve as you solve one part and expect to fix but it seems like it is still there since it is only part of the problem adding to confusion. (Edited the intro as I no longer think I am a cliche DIY throwing parts in to no avail)
As labor was practically free when doing myself changing too many parts was also partly future proofing the engine.
Any suggestions on what to look for next? I hope the level of detail below would help shed light to this.
Car: 2014 SL 63 AMG
M157 5.5L Engine
64000 miles.
SYMPTOMS:
- Was fine for several thousand miles initally.
- The car isn't tuned.
- Started chirping the belt whenever I revved the car at idle sitting still or driving with sport+ when the ac was on (compressor load).
- The chirping only happened when the rpms just started going down, you lift your foot from throttle at standstill or a fast upshift (in sport+) is complete.
- Video of it is attached below, when the rpms start going down, the tensioner unloads, belt unslackens and the AC compressor stops because there is literally no tight belt at that exact moment and then the tensioner recovers (as the engine torque recovers) and the belt restarts the stopped compressor kind of immediately and during that very slight belt slip it chirps.
- Even when the AC is on no chirping happens in Comfort mode as the transmission doesn't shift aggressively.
WHAT I DID MYSELF AS DIY:
- Replaced the belt and the tensioner with genuine ones from Mercedes-Benz. No change.
- Checked alignment and realized the water-pump pulley walked out. I know it happens with these engines, I didn't press it back as surely the impeller would have been bad. I replaced the water pump along with the usual plastic hoses that break all the time and the thermostat. The impeller had small broken parts so I flushed the cooling system. Belt became aligned with waterpump pulley but still chirping.
- This car uses a clutchless AC compressor. It is two pin only and there is just the control valve. (Unlike the similar M278 4.7L engine which 550 model cars use that has 4 pins and has both a clutch and a control valve) I replaced the control valve and no change.
- Replaced all three idler pulleys. They were fine though. No change.
- I replaced the AC compressor and drier with mercedes genuine. The compressor was mercedes remanufactured. Mercedes remans are usually very good, they could even be unused returns. The AC was always cooling very well. Initially, after control valve change and recharge and after compressor and drier change and reharge. I check the temperatures both from xentry and vents and also vacuum fill to exact grams as I have HVAC certification and I have 30lbs refrigerants which makes it possible to recharge perfectly. Still chirping.
- I replaced the Vibration Damper (Crank Pulley/Harmonic Balancer) and no change!
- BTW the Alternator can be hand spun freely (of course when the car energizes the coil it would be harder but I don't see it causing this much trouble on the belt system like hard slapping but feel free to comment)
- Hydraulic pump can also be hand spun easily and the ABC suspension works well, ride height changes quickly, no leaks, no errors.
- I take care with torque specified with every bolt in the service manual and follow it closely to do a good job.
CURRENT STATUS:
- Car runs and drives well except the chirping at specific conditions. No chirping with comfort and AC on. No chirping with Sport+ and AC off. Chirping with Sport+ and AC on and chirping when revved at idle when AC is on. (Same as the beginning)
- As the belt slap is hard on the components and I don't want to damage anything else, I configured the AC button from Xentry to instantly disengage the compressor if I want to drive with Sport+ on temprorarily as bandaid.
- I haven't checked the PWM signalling to compressor control valve yet. I have a professionnal oscilloscope with both analog and digital logic probes. I am not sure how the ECU would change behaviour on this.
- There is a setting in xentry that disengages the compressor with wide open throttle but it doesn't apply to V8 engines.
- I have access to WIS electronic service manual and all the necessary tools.
Thank you all beforehand.
ADDITIONAL INFO:
I did a breaking-in adaptation for the new compressor from Xentry and it is "almost" perfect now. So there is finally an improvement. Mostly doesn't chirp anymore. And if it does, it resolves itself when you turn the ac off and back on. I need to focus on TCU ECU etc, they should be signalling the ac control unit to temprorarily unload at the exact moment. Any suggestions are welcome.

EDIT:
Thanks to a user in another forum's suggestion, I learned about the alternator pulley's one-way clutch which is probably the last piece of the puzzle and explains why it is mostly resolved but still ocassionally happens as the alternator load changes dynamically. Also those hard belt slaps over time would have killed many of these even if initially started with one component. I will be checking it soon as the engine still hot.

EDIT:
Checked the alternator pulley and it is fine. The car didn't make chirping today BTW, so it is as almost fixed like yesterday, maybe needs just a little more auto calibration.

 

That’s a strange one,
Seems like it may be something other than AC. Though AC load may play a part.
Looks like you’ve done your due diligence….

Does it matter if car is cold or hot?
How about ambient temps, does it matter if it’s cold or hot?

 

Doesn't matter hot or cold. Also it is Miami, kind of always the same temp.
What I think is, it is a belt load and control unit AC compressor control valve unload timing issue. Since this AC compressor on M157 doesn't have a clutch (M278 does have a compressor clutch while being almost the same engine) the signal to reduce the ac compressor load can only be done by the control valve and calibration of that and the how worn the AC compressor is (even if it is only 64.000 miles and working ok) how fast it responds affect it.
These engines have a habit of water pump pulley walking out, which affects the belt alignment. Vibration damper getting older (not due to miles but more to age, in this case 11 years) all of these combined each contributing slightly exceeds a threshold where ac compressor starts locking up due to belt slap and then it is downhill from there. Basically that explains why changing an obvious bad part doesn't seem to solve it but it is actually part of the solution. One could possibly only reach a fix when many parts are replaced and each time since the chirp is still there it gets more and more confusing adding to the feeling of DIY issues but I no longer think that is the case as I have consulted some people in mercedes-benz authorized services and they are more baffled than I am.
The first time there was a huge (almost fixed) improvement was the breaking-in adaptation of post ac compressor replacement from xentry AND driving the car a while. Good part is car is consistent about it, not fully random.
As of now it almost never does it anymore, but occasionally I can hear it (but to lesser extent) while hard driving but one important thing to note is whenever I come back it starts chirping at idle rev up but a powercycle in A/C button fixes it. (I wait enough for compressor to reach full load, I use max cool button, I also see control valve command current as full and still doesn't chirp anymore)
Basically, there were mechanical parts involved and now it is more of a calibration/adaptation a this point.
One thing to note though, I got a mercedes remanufactured ac compressor, while mercedes remanufactured parts are almost always perfect, I cannot blindly rule out the new compressor having partly some more drag or slow response compared to brand new (which seems to be no longer available) though I don't think so.
In any case I am quite happy that I was able to come from no change at all to almost fully fixed and continue to look for other stuff, maybe analog and digital scoping the PWM to control valve.
I can even implement microcontroller based custom circuit which would modify pwm signal to ac compressor under WOT (thus reducing belt load temprorarily), that is within my electronics capabilities, not planning that as of now but as a last resort.

 

Whoa, just got a chance to look at the video you attached, I wrongly assumed it was an audio file.
When you said "chirping" I thought belts, (which it is) but that looks like it's getting a huge load and almost locking the belt. Something is definitely off there for sure.
I'll have to look at my friend/customer's s63 to see how aggressively the compressor engages. I have an M278 in my car so that won't really help. Maybe someone here with an SL63 can compare their engagement.
Hopefully the adaptation will come 'in line' as you drive it more, but that seems like quite a bit of load from that AC compressor.

Good Luck.

 

Let's split this to two parts. I write walls of text, while detail is good, it is difficult to keep track of.
- Most 63s have the MCT (same transmission but a clutch instead of a torque converter) Transmissions with locking torque converters could still shift as brutal as MCT in Sport+ mode but many of them don't. (The software isn't adjusted for that)
- The issue does kind of never happens in comfor mode even max acceleration as MCT very noticably slowly and smoothly shifts which reduces the abrupt torque loss on the belt. Sport+ does the opposite and thus chirps more.
- Focusing on the standstill idle is more important IMO. You can just rev up the car by just pressing the pedal for a very short time so that it goes like around 3K rpm at most, it very quickly goes down and that exact moment where you lift your foot and the RPMs/revs start going back down this happens. That is the point the engine abrubtly looses torque and the belt becomes loose and the tensioner isn't fast or stiff enough for that. (I have brand new genuine tensioner)
- If you press throttle too long so that it goes high wnough like 4K+ then it becomes a soft limiter and turns back smoother and thus doesn't chirp.
- All these prove that this only happens when the belt abruptly looses engine torque on it, loosens, and tensioner isn't enough, and AC compressor locks temprorarily because there is the high pressure refeigerant pushing back on its swash plate/pistons and when it restarts the belt slips a little and that is the chirp we hear. BTW it is not in the video you saw but the belt part going towards the ac compressor widens up like more than an inch while the compressor is locked and then when the crank pulley starts pulling tensioner comes back, belt covers ac pulley fine and forcefully spins it from the locked position. I believe the car already believes the abrupt torque timing has passed and releases the ac control valve to load back but actually the belt isn't tight at that moment and there is no compressor speed sensor.
- Yet this is not a cosmetic slight belt slip noise as that hard belt slap eventually destroys a lot. Basically my water pump pulley walked out first, and then the belt slipped off. But the chirping started way before this and the water pump pulley was slightly outwards. (It may have been the trigger to start it all)
- Important details to note ​​​: Before I started educated parts throwing the car chirped "badly" every single time. The amount of chirp (thus the belt slip on ac) was dependent on how much the ac was loaded and it was worst when it was at max cooling (thus max drag) NOW it almost never does even it AC at max, so this would mean many partial contributions like walked out water pump pulley, misaligned belt, 64.000 mile partly worn tensioner, all the idler pulleys and other pulleys that glazed a little, ac compressor that was dragging a little that I fixed made it possible to reduce the belt load to reasonable levels and the adaptation better controlled the timing of the ac compressor control valve unload.
- What is left: When leaving home, it doesn't chirp at idle hard rev with max ac at all. Which is really good. But when coming back home and in the driveway it starts chirping at idle when revving hard. Of course I am not revving my car at idle normally, it is just to see if problem is still there. I then turn off A/C off and back on and no more chirping even at full ac load. Also when driving it almost never chirps anymore when shifting with sport+ and it used to do it every single time even when not driving hard. But still under specific conditions I can hear it chirp a little, meaning I was able to increase the threshold a lot and mostly fixed it but there are still some conditions (maybe when alternator is also on high drag and 5K+ shift etc) it still still chirps (but less then usual)
- While it is mostly a success, I cannot mark this is complete as it will still eventually lead to same failures again unless it is completely gone and is exactly how it was before.
I will try to do breaking-in adaptation again. Possibly it affects the calibration WHEN you do it. I don't have direct access to technical data that would explain what breaking-in adaptation does. WIS electronic service manual doesn't even mention it. It just says install in reverse and recharge but Xentry says breaking-in adaptation is required after ac compressor change.
- A stiffer tensioner (although bad on the wholr system but I am not planning to drive this car 50.000 more miles) could fix it too but not sure if that exists.
- I forgot to tell that a slightly (10mm) shorter belt didn't change anything as the belt is kind of completely loose and even shorter belt isn't covering the compressor well at that time.
- The bad remedies like belt dressings and such also don't work. (Tried but they are no longer on any part, either cleaned or replaced.

 

We all have different writing styles. These cars are technical and getting details is important, but it’s helps to parse information presented, to relevant details to help remote diagnostics…
We’re all pretty well versed here with the MCT. This is happening in PARK. Transmission is disconnected. while we can see the correlation of why the AC clutch is different on the AMG cars. Your issue is separate, though possibly exasperated by load.
“kind of” eludes to - it’s still there, while it may not be chirping, I’m betting that tensioner movement is still pretty substantial.
Yes, We can see that in the video. It’s definitely an abnormal load on the engine from the AC.
This is why I believe this may be electrical, or possibly adaptation related, but can’t help to think we’re missing something here.
100% agree the two are interrelated, this isn’t a common failure, it can happen, but the pulley is pressed on fairly tightly to the impeller shaft. Let me tell you my theory, the water pump is rotating then being stopped, as this happens over time the impeller shaft starts to spins on the impeller, slowly working its way loose. It’s kind of a chicken or egg thing. Which came first is hard to tell, but make no mistake, this isn’t a coincidence. I believe your AC is what caused the impeller to walk on the shaft. Force of momentum should not to be underestimated….
Like most things on these cars they don’t cope well with tolerance stacking. Lots of little things can add up to major issues. I believe adaptation could be an issue, I can’t help but to think we’re missing something electrical wise. I’m assuming XENTRY never kicked out any codes?
THIS IS A CLUE to a deeper issue.
Honestly the on and off thing points to electrical vs mechanical.
I’ll look on my copy of the WIS to see if I can find anything relevant, but that isn’t something that adaptation would affect.
Unfortunately it may be a while before I have access to that S63 again and my other customer/buddy who had an R231 - SL63 now has an R232
Exactly, you may have reduced the chirping for now, but it will eventually lead to the water pump walking out again or possibly a much worse failure at the least expected time.
I think it’s worth a shot for sure, I also know that sometimes adaptations need time to re learn. XENTRY can tweak it, but best results come from driving. Problem becomes when it’s destructive to other systems. As an example, transmission adaptations can take time to refine under actual driving conditions. They’ll usually get you close enough to be able to drive the car for final adaptation under driving conditions.
Thats a pretty kludgy fix, you’ll want to find the actual problem, but not telling you anything you don’t realize
I’ll have a look at my copy of the WIS to see if I can find anything relevant. But a lot of the AMG specific stuff can be somewhat vague as you’re well aware…

Good Luck!

 

Thank you for the detailed reply. Here is additional info that I had missed to type before, answering your questions:
- No errors on any related modules (hvac, ecu, tcu etc) in xentry. Zero. I believe the car isn't aware of it. Smooth running actual values also seem fine.
- I agree the tensioner would still be moving a lot and chirping would only occur when belt is temprorarily loose enough at the same time with high AC demand but it would still be hard on everything. I am not trying to get rid of this chirp, it is just a gauge of the existence of the overall problem.
- The reason I wanted to split in two was, although it is always the same reason it chirps, focusing on driving and standing still just proves some points, it only happens at abrupt slow down of the belt which normally happens with every single car and the tensioner and the control valve unload logic, harmonic balancer/vibration damper and the one-way alternator clutch are all there to remedy this.
- About the water pump pulley walking out, let me give you details as I inspected my old pump. The bearing was still in its place. The impeller and the pulley was still in their correct position relative to the shaft (so their distance was identical) But they moved out as a whole. With a press tool I was able to press them back to original position (with precise measurements I made from the new pump) buy when walked out the impeller touched the water pump body and the enclosed side of it had broken parts (which isolate the water flow so that only the vanes push it and it doesn't mix) it was still working btw, probably with less efficient flow rate. I flushed the whole cooling system removed hoses but couldn't find any broken impeller parts, they are probably buried in the radiator bottom and won't cause problems. From the flor direction I believe broken pieces were towards radiator bottom.
- I watched many videos that mention water pump pulleys walking out on these engines. I think it is actually common but there aren't enoughold R231s yet.
- WIS doesn't even mention breaking-in adaptation. I saw it in Xentry and it said it needs to be carried out when compressor is replaced. While it certainly is mechanical + electrical AND a calibration could sometimes hide the issue to an extent as it is it's job to calibrate to current condition of the whole system so it is capable of "mostl" calibrating within its range and it actually did. A temprorary win rather than constantly slapping the belt and quickly destroying stuff.
- To keep things working in the mean time, I adjusted from Xentry to immmediately turn off A/C compressor when A/C button is pressed. Normally it is delayed to remove moisture in condensator to reduce mold risk and smell. Pressing the OFF button does always turn off compressor immediately but also turns of the fan. You would do hard acceleration for a very short amount time so just temprorily I press the A/C button, fan still on so I don't immediately feel hot in Miami, the belt load is very little and then I turn that back on. I4 and V6 engines have this by default, under WOT their comprrssor are always turned off instead of just when shifting. Xentry says the setting for that doesn't apply to V8s and I tried, yes it doesn't. The setting in xentry tries to prevent smaller engines from stalling.
- Initially I though I had become the cliche DIY guy throwing parts and achieving nothing but after talking with people includining foremans in authorized dealers I see that this isn't something you know from experience and swap it and be done with it as it reaches a point where the time 0 point leads to other worn parts, lost calibrations, it gets messy over time. (And this doesn't usually happen with the Japanese, it is a pity I don't find Japanese cars to apply to me)
- IMPORTANT: Since I have all kinds electronics tools and experience, not just cars, when I have time, I will be scoping the AC control valve signal with both analog and digital logic probes to find a correlation with the last remaining chirping. I first though maybe PWM signal "high" weren't fully reaching Vbat or Vgen thus reducing average control valve voltage but than I tested a control valve and it pulls the control valve, opening the orifice, I believe more pulse is more compressor load so that wouldn't be the case. THIS IS STILL POSSIBLE: From WIS I have seen it is not the ECU but the ac control unit that controls the control valve. But it takes info from tcu and ecu like speed, torque or direct off requests. While I do see ac control unit aware of the engine speed I need to check (even sniff can or lin messages, I have access to both with self designed custom microcontrollers where I can put my circuit as "man in the middle" even modify on the fly) I would like to see the pwm shape during rpm downs and whether it changes when it chirps.
- I am not sure whether running a breaking-in procedure would have made any difference before I started replacing parts but it says it is ONLY needed after compressor replacement which I hadn't done, hence didn't do it.
- The water pump pulley wasn't this out when it first started chirping. While I don't exactly know it's position when it first started chirping, when I started checking it was like a few mm off or at least the belt wasn't centered on it and didn't have a gap on the inner side. Over a short time it walked out like half and inch and the belt slipped out.
- Sorry for the wall of text but I believe this deserves it.
- Before I had any improvement it was ALWAYS the same amount of chirping in same conditions. Now it is never or little and that ac reset fixing it is interesting.
- ONE LAST IMPORTANT DETAIL: That ac/on off thing, the first rev after that has a little chirp and the rest have literally zero chirp even when max cool on. This should mean there is an additional on the fly temprorary calibration logic going on. Like the ECU calculates something on first rev down and compensates for it. I know there is the smooth running logic which keeps track of engine pulses and vibration. I will look into that again in motor electronics actual values and before compressor PWM, let me try to see if anything differs on engine readings when it chirps (like it looses torque too fast when rpms are going down?)

 

I did another breaking-in procedure and unfortunately it is back chirping and pretty badly (This time I did calibration after the car was driven quite a while). At least I know where to focus on. The control valve unload timing is getting incorrect and adaptation affects it greatly.
I will do a calibration later on with a just started car and do the pwm signal scoping. The breaking-in adaptation should be looking at what happens when control valve current is changed and if something is unstable about that in my car it would calibrate incorrectly. The control valve is supposed to follow pwm signal AND on time, so does the response of the swash plate inresponse to the control valve. Although I did replace the drier and recharged with correct amount of oil per WIS and all measurements and AC performance is OK, I did not fully flush the system. Since at this point I am looking at anything, I would like to know anything that would slow down swashplate response even with correct control valve PWM signal and correct timing as well.
BTW checked and tested all engine parameters in xentry both idle and full load they all came up all green. Engine is working pretty well. I have the screenshots but it is like 20 of them.

 

Per CharGPT below, it actually makes sense as my first adaptation was cold and second was hot. I am an IT guy with 25 years of experience on IT and about 10 years in AI (way before ChatGPT was a thing) Although it fails frequently, AI's responses are based on hundreds of other forums where people had similar issue with their AC compressor, in my case it results in the chirp because of how the M157 is built. Basically I will do a cold breaking-in as I had planned before.

ChatGPT:

What the Break-In Adaptation Procedure Actually Does

This is specific to Mercedes-Benz (and similar VAG/BMW platforms) using externally controlled variable displacement swashplate compressors, like Denso or Sanden variants.

The break-in adaptation is an ECU function that:

✅ 1. Resets learned swashplate control characteristics

• It resets internal adaptive maps for how the ECU modulates PWM duty cycle in response to ambient, cabin, and refrigerant pressures.
  
• Old compressor behavior (e.g., stickier swashplate or leaky control piston) may have caused the ECU to learn overcompensation patterns — the new compressor doesn't need that anymore.
  

⚙️ 2. Initializes control valve stroke mapping

• Some break-in routines sweep the valve control range to calibrate how much stroke corresponds to each PWM value (especially when it's not linear).
  
• This is critical when replacing only the valve or installing a reman unit — the flow curve can slightly differ even between identical parts.
  

🌀 3. Relearns refrigerant pressure correlation

• The ECU monitors pressure sensor feedback (typically high-side) and expects certain pressure responses to PWM commands.
  
• The adaptation may "teach" the ECU what actual pressure rise/drop results from commanded displacement changes.
  

🧪 4. Clears stuck residual modulation

• A compressor that failed or had erratic control may leave the ECU in a semi-locked PWM behavior mode.
  
• Adaptation routines often clear stored faults or fallback values that inhibit proper modulation (like defaulting to max displacement).
  

⚠️ Why the First Adaptation Helped but the Second Made It Worse

✅ The first adaptation:

• Likely cleared old compensation values and re-synchronized PWM → displacement mapping.
  
• The swashplate responded correctly for the first time, improving performance.
  

❌ The second adaptation:

• May have been done too soon, without sufficient runtime data, or under poor conditions (e.g., hot engine bay, low refrigerant mass, or uneven thermal load).
  
• It might have caused the ECU to learn skewed values (e.g., it thinks more PWM is needed than actually is), causing delayed response or over-displacement under low loads.
  

🧠 Summary: What the Break-In Adaptation Actually Does

Function Purpose Resets learned swashplate behavior Clears bad adaptation from old compressor Maps control valve PWM vs. displacement Ensures ECU understands how the valve responds Monitors pressure response to PWM Syncs expected pressure behavior to actual feedback Prepares for clean compressor control Prevents stuck control states or limp modes

 

Just to confirm your new part is 000-830-45-02-80?
It seems like you’re on the right track with adaptation. I think you may need to adjust it until you get proper results. The fact it got worse, after you adjusted it hot means the adaptation is effective, just was in the wrong direction. Know anyone with an icebox you can drive your car in?
You may need cooler temps to run effective adaption….
And as I mentioned above, you may just need to get it operationally close so it doesn’t destroy any parts (water pump), and drive it to complete adaptation.

Just to give you an idea. Below is probably what your pulley looks like. You can see it is more dampener more than a “clutch”. The M278- M276 is similar but looks like more forgiving as fas as initial engagement. Closer to a traditional AC compressor clutch.

So getting the right “slip” is extra critical on the AMG cars….


I’ll try to reach out to a guy I worked with who was pretty savvy on AC systems. I was never the AC “go to guy” in the shop…
See if he’s seen this before.
(Btw no joy on my copy of the WIS for adaptation)




This is your old compressor, no?

 

Thank you for your reply. Yes, the new compressor I got is A0008304502 (80 at the end as its remanufactured) but that is just a Logistical replacement for A 003 230 56 11 which was my old one, meaning they are the same compressor. And yes the pulley looks like that because of the lack of an actual clutch there, that dampener piece is always engaged and is also meant to protect the engine in case of hard failure.
About the slip on AMG cars, that slip only works when the compressor load gets high in a tensioned belt, not the other way around because when the engine toque is gone just at the moment of rpm drop (whether idle revving or upshifting) the belt just goes so wide that it is not even driving the compressor. That is why a 10mm shorter belt did nothing. This could only happen when engine stops pulling belt hard, this is the time tensioner move to keep belt tight and alternator pulley prevents alternator load from pulling the belt. In my car there is too much load on the belt so when the engine is NOT pulling the belt for fraction of a second it goes loose and tensioner bottoms out.
In the video I posted it is not seen but I know the belt that is coming TOWARDS ac compressor goes OUTWARDS more than an inch. This could only happen when there is still compressor load at that moment and the belt just goes out rather than drive the compressor and the compressor locks as there is no friction anymore. Than the crank starts pulling again (revs went to idle of upshift complete) and tensioner stiffens the belt, belt restarts the compressor forcefully.
Normally, to prevent this, the car (the ac control unit with information coming from ECU and TCU) lowers the pulses to control valve to basically lower AC compressor load just at the right time so that it is easy to turn and belt never slackens and tensioner never bottoms out. In my car, either the signal is early, or not enough or such that they are not in sync. What's making it worse is as the car thinks it is all over and increases pulses to AC compressor it becomes very hard to start so the belt must slip a little until compressor starts again. The damper does little in that case because basically it is a non-rotating compressor with a fully engaged swashplate.
BTW M278 compressor has a "physical clutch" in its pulley along with two extra pins to control it (Total of four wires). M157 compressor is clutchless and the damper is there to protect the engine in case of catastrophic compressor failure in addition to the damping. In compressure failure that damper just gets distintegrated and pulley continues rolling regardless of compressor shaft locked.
Basically you cannot mount the M278 compressor on M157 as the plug won't fit and you don't have the wiring or software to control the clutch so it will never engage (It will just spin freely without spinning the compressor shaft at all) and the AC will never work.
I appreciate reaching out to your AC guy. Please ask about swash plate responding late or not enough to control valve pulses and make sure you tell him it is a clutchless compressor with only two wires going to the back, the control valve for the variable displacement. I would love to get his insight whether anything else in the system would cause the swash plate to repond slower or less to control valve orifice moving. The AC does work very well and always did and since I vacuum and recharge myself (I am HVAC certified so that I can get large tanks of refrigerant to correctly charge by weight) I would love to know if other parts like condenser, expansion valve would have any affect since two compressors, one not that old (only 64.000 miles, as compressor usually go really long) and the other basically new. I replaced the drier with the compressor but didn't flush the system. Added correct amount of extra oil per WIS for driver and compressor replacement which was 30ml. Also it doesn't sound like it is low on oil or doesn't have cooling problems and I measure both with Xentry and thermometers inside vents.
As per the temps, ChatGPT said (as its based on hundreds of forums on AC compressor talk) the calibration should have been done with cold engine. Actually I did my first adaptation just after I started the engine and it pretty much fixed the problem mostly. (But NOT 100%, still I'll take it for now)
Tomorrow, I will start the car and as soon as idle is down (which take only a few seconds in Miami, I will redo a adaptation. I will start the car without the A/C engaged and connect Xentry beforehand with just ignition.
I am still planning to scope the pulses to see the timing and strength is incorrect or is correlated with the chirp later on but I will give it some time to learn. After the first calibration and it was mostly fixed, it only chirped "once" I parked and subsequent revs were OK suggesting ECU changes something based on the first rev. It is still not the ECU that sends the pulse. ECU and TCU communicates with AC control unit. I will also check that. I have seen AC control unit see the engine speed but possibly it is missing some important messages or timing about engine torque so that it could unload the ac compressor.

 

ChatGPT also said the following below, I will check the pressures with digital gauges and compare them to values in xentry.

Pressure Sensing/Logic Fault (but no DTC)

• If the pressure sensor (typically high-side) feeds values slightly out-of-spec, the ECU may believe the load is still high and keep PWM on.
  
• No DTC would appear if values are within range — only response timing would be wrong.
  

 

I recently replaced the AC compressor on my 2014 SL65. The M279 engine also takes a compressor without a clutch. I guess it was dumb luck, but it's working perfectly and I did not do any adaptations, mainly because I didn't even know they were needed.

I'm in way over my head here, but what I would have done is replace the AC compressor again. There may actually be something wrong with your remanufactured unit. The only other thing would be to make sure you're not overcharging the system. I put in the exact weight specified in WIS, which I think in my case was 550g.

It's probably worth noting that I did not buy a remanufactured unit. Instead, I bought a new aftermarket replacement. The unit came with the proper amount of oil in it. Not sure if the remanufactured units do that?

 

Thank you for the reply, the issue was there before the AC Compressor replacement, didn't come with the new A/C.
I checked and M279 uses the exact same Denso compressor as M157 just with a different connector facing other direction so a different mercedes part number, clutchless as you said.
Your could be fine without adaptation if other parts of your belt system are fine and also M279 doesn't have MCT clutch and heavier and better balanced V12 crank falls back down in revs is smoother.
I have HVAC certification (not my profession, just to buy refrigerant) so I am able to get 30lbs tanks to weigh them perfectly while recharging to 550gr+/-10. I also followed the 30mL additional compressor oil as suggested by compressor and drier change in WIS.
After all this effort I have almost confirmed this is a timing issue where the ac control unit fails to unload the control valve in exact timing OR the swashplate inside the compressor reacts slower which could be because of other parts of the A/C system.
I am currently planning to do adaptation with a cold engine where it seems to do way way better and then check the pressure sensor reading vs a professional digital A/C manifold gauge.
The range of refrigerant pressure is 0 to 35 bars which is quite large so it wouldn't log any errors. Xentry normally shows around 13 to 15 bars on high side which is mostly normal BUT if it is off from the real value then the control valve PWM signals would be off.
I also have a professional oscilloscope that also has digital logic probes, I will look at the signalling in real time to see what is different in both the timing and frequency when it chirps or not.
Seems like I can scope from within the car as climate control unit controls the compressor control valve with data from esp, tcu and ecu. I have the wiring diagrams, just need a proper setup like needle puncturing probes. I will do it soon but I will post the 3rd adaptation (cold engine) results soon. (1st was cold and worked very well, 2nd was hot and messed up)

 

I checked the wiring diagrams and the compressor control valve is NOT directly controlled by the AC control unit. AC control unit REQUESTs it from the front SAM control unit over CAN B and that physically controls the valve. For non-AMG cars with compressor clutch there is an additional request for the clutch which doesn't apply here.(Code B09 is magnetic clutch and signal is 7, U462 is the clutchless compressor)
Not seen in the following screenshot, The CAN B messages are as follows:
5: Refrigerant Compressor, request (This is the signal that asks Front SAM to turn on the compressor, it should contain realtime values of how much)
9: Idle speed increase, request (In case a higher idle is needed)
10: Fan motor, request (Asks for radiator fan to turn on even when engine doesn't require it)
12: Coolant circulation pump, request (This is the secondary electric pump that circulates coolant on intercooler (charge air cooler) and turbos)

FROM WHAT I CAN SEE ECU does not communicate with the AC Control unit directly. It communicates with the front SAM over CAN E1 and it is about 9 idle speed increase request, 10 fan motor request and 11 is the actuation of the motor directly from the ECU.
6 is the Compressor actuation (that I need to scope) and 8 is the magnetic clutch actuation which doesn't apply on this car's clutchless compressor. The actuation signal is between front SAM and compressor.
Front SAM has fuses and relays on it BTW.
CAN B is interior CAN 2 and Chassis CAN is CAN E1 and Chassis 1 CAN is CAN E2, these are the CAN buses on Front SAM.
Instrument Cluster, COMAND Control Unit, Analog Clock, Emergency Call, HERMES, Live Traffic, Fuel Pump Control Unit, Motor Electronics, ESP, Overhead Control Panel, Door Control Units, Diagnostic Connector are directly connected to Front SAM.

From the AC Control Unit diagram, it's only DATA connection is to front SAM. All other pins are directly connected flaps, sensors, blower etc. So it only has access to CAN B.
Motor Electronics and ESP are communicating with front SAM through Chassis CAN (CAN E1)
Combustion engine control unit function focument doesn't list controlling or requesting compressor unload and it doesn't transmit torque info.
Powertrain control unit serves as an interface (gateway) between combustion engine control unit and the ESP + related CAN buses.
ESP seems way more involved in everything.
Motor Electronics connect to Drive train CAN (CAN C)

I AM FOCUSED ON finding out what determines the control valve pulses other than the 0 to 100 actuation request from the AC control unit. As front SAM is sending the pulses, I will be scoping from there. Since I don't see a way for the AC control unit to listen to ESP, ECU, TCU related stuff on CAN B, it would be either the front SAM adjusting the compressor control valve signaling based on Chassis CAN (CAN E1) info from ECU/ESP/TCU or it sends that information over CAN B to AC control unit for that to respond but I don't think so.
Due to lack of engineering documentation it is not fully clear which module stores the adaptation data and which module is responsible for additional actuation on the control valve other than the regular AC cooling functions. But I am on it. Scoping might shed more sense to it.

THE WIRING COLORS for A9 clutchless compressor: The wiring diagram for front SAM is a mess. It has 6 separate sheets so you need to be looking at the correct one. pe54.21-p-2106-97rkc (c at the end) is the one that contains compressor connections. It is the Model 231 Sheet 3 called Wiring diagram of front SAM control unit with fuse and relay module (N10/1)
Yet this document only shows clutchless compressor to be valid for M279 V12 engine. U1035 is the M279 engine, U1018 is the M276 engine and it says for MY2014+ U1032 is valid for both M278 and M157. I know the M157 compressor DOES have a 4 pin connector despite only having two physical pins in it and the M279 compressor has a smaller 2 pin connector.
This makes M157 a special case where the 4 pin connector of the M278's clutched compressor is used but with half the wires.
In any case it doesn't show a 4 pin connector with 2 wires going to a clutchless compressor on THIS document.
Let me just write it just in case, I will check my car physically later.

For M279 V12, two pin compressor connector. (Note: Engine harness side is pin numbers 2 and 3)
FROM Engine harness TO compressor control (regulation) valve: GREEN/BLUE (x1) and BROWN/BLUE (y1)
FROM Front sam TO engine harness: GREEN and GREEN/BLACK (Connector: X26)

For M278/M157 (which is kind of incorrect for M157) (Note: Engine harness side is pin numbers 2, 3, 14 and 13 in order, pay attention to last two pin numbers reversed)

FROM Engine harness TO compressor: 1-RED/YELLOW, 2- BROWN/YELLOW, 4-BLACK/YELLOW, 3- BLUE/YELLOW, pay attention to last two pin numbers reversed)

FROM Front sam TO engine harness: 1- BLUE/GREEN, 2, GRAY, 14 RED/BLUE, 13-GROUND/BROWN
On the M157 two of these should be non-existent. I will have to check for actual colors but since pin 13 is GROUND and M279 doesn't have ground on its control valve only connector I think it would be the same as pin 1 and 2 and I can confirm my wires towards the compressor connector contains YELLOW (didn't check throughly but it is visible from the sleeve) while M279 diagram doesn't have yellow. Thus I believe control valve is Red/Yellow and Brown/Yellow on the compressor side and Blue/Green and Gray on the front SAM side. Since Brown is ALWAYS on the second pin and the actual wire that goes to the control wires and clutch are always red and black, while probing pin 1 is the positive pin 2 is the ground for that circuit. (not the car ground)




BTW, per Chat GPT below, it is Front SAM that decides on how to control the compressor. ChatGPT can only make sensible answers when it is fed good info and multiple times which I did. It just doesn't immediately give you a correct answer. So any GPT response I post is result of hours of conversation with it. Anything I have written above is BEFORE ChatGPT's answer as those findings improve ChatGPT's responses rather than blindly asking and posting what it says.



Breakdown of Control Responsibilities

🧠 1. HVAC (A/C) Control Module [Interior CAN – CAN B]

• Stores: Climate settings, target vent temperatures, user settings (ECON, max cool, etc.).
  
• Sends request → Front SAM via CAN B.
  
• Does not control the compressor directly.
  
• Does not store adaptation values for the swashplate/PWM curve.
  

✅ Acts as a client, requesting cooling performance — but cannot modulate displacement timing or predict torque events.




🧰 2. Front SAM (Signal Acquisition Module) [CAN B, CAN C, CAN E1]

• Acts as the actuator gateway for the A/C compressor control valve.
  
• Receives:
  • Temperature & load requests from HVAC module via CAN B
    
  • Engine torque status & RPM from ECU/TCU via CAN C
    
  • Brake/traction/ESP activity via CAN E1
    
• Outputs PWM to the compressor control valve.
  

✅ This module executes the actual swashplate control (via PWM).
✅ Stores adaptation values related to PWM → displacement correlation.
✅ Implements unloading logic during transient torque events (based on CAN C and CAN E1 input).




🏁 3. Engine Control Unit (ME – CAN C)

• Broadcasts torque load signals (actual & requested),
  
• Notifies other modules of gear shifts, throttle lift, deceleration,
  
• Also coordinates with ESP and transmission for load management.
  

✅ Does not control the compressor directly, but is a major influencer of the logic used by Front SAM to unload the compressor at the right time.




🚗 4. ESP Control Module (CAN E1)

• Detects drivetrain dynamics: yaw, brake pressure, decel rates, torque cuts, etc.
  
• May participate in preventative load shedding, especially during aggressive decel or traction control events.
  

✅ Feeds Front SAM with hints that compressor load should be reduced (preemptively).
⚠️ Not usually the decider for compressor unloading timing — it contributes input, not decisions.

 

Last adaptation with cold engine resulted in a pretty bad calibration, chirps and locks as hell. Even after driving for a few days. I will be scoping the PWM signal and report back.
Also the digital pressure gauge is arriving tomorrow.
I realized the high-side pressure accuracy of Xentry is pretty bad when set to european units. It just jumps from 12 bar to 13 bar or so. Which is like vlose to 15psi jumps. I set it to US units and now it shows in psi like 176 177 etc so very accurate.
I will also check expansion valve condenser etc. (To see if pulses are correct but swashplate response is slow)

 

There is a lot of talk about engine mounts being related to belt noises, causing belt tensioner slaps even pulley misalignment. Also on M157 they are advised to be replaced 50K to 100K miles or 5 to 10 years regardless of lack of symptoms. My car is 11 years old and 64K miles and I am assuming they are the original mounts. Any comments on engine mounts and its effects? I guess I will replace them anyway due to both miles and age but any information would be very useful. Engine itself doesn't move at all when revving from idle btw, but haven't checked otherwise visually yet. I have a automotive endoscope to look at the mounts.

 

Based on your original video I'd say your motor mounts look okay. The engine isn't moving at all. From that video it does seem apparent that something driven by the belt is locking up and that most likely something is the AC compressor.

An issue with PWM signal to the control valve could be a cause. But it's not clear how those signals could have become invalid since they're software driven. Problem seems to be pointing back to the AC compressor and/or the control valve not responding correctly to the PWM signal. I wonder if this was a defect in some of the manufactured units and your reman was one that just got put back in stock?

On a related note: I'm curious what you're using to log messages on the CAN buses?

 

Thank you fory your reply.
- With the original compressor, I did replace the control valve with a 3rd party one and it didn't make a difference. Both seemed to work with a pulse generator outside the car well. I didn't do an adaptation for that though.
- The remanufactured compressor has the new "mercedes" part number. (Denso part number is almost the same) Although that part number change is listed as logictical it still means they are years apart, I believe that makes it unlikely to have the same issue due to manufacturing but I cannot fully rule out them having the same issue but still unlikely.
- I have identified the front SAM and the connectors despite the incorrect info im WIS wiring diagrams and will scope soon. I will shoot video for me to watch while scoping to time match/compare the revs to pulses.
- The digital AC gauge is coming today for comparison of pressure sensor reading vs real pressure. (I have analog gauges too, will also use them)
- I checked the high-side pressure while driving and they were quite OK. The A/C cools very well along with temperature readings and has always been like that and I was the one vacuum recharged it twice.
- I have straight edges coming today. Although it looked OK I will check all the pulley alignments with various length straight edges this time. Just to rule it out fully.
- Although I haven't replaced the condenser, it seems highly unlikely as the A/C is cooling flawlessly.
- I also have a new 3rd party pressure sensor for testing. The pressure sensor is in an easy to reach area but looks like M157 doesn't have a schrader valve there? Would it really require capture and recharge for a pressure sensor change? Anybody has information this? Many cars just seal the refrigerant when the pressure sensor is removed but this pressure sensor has just a hole there with nothing to push a schrader valve.
- For the CAN and LIN buses I have custom made arduino and teensy microcontroller + tranaceiver based modules. I did a lot of work with LIN before including on the fly changing of data or custom adjustments etc. With CAN I can capture them to later identify with software to Mercedes IDs and messages and such. For now I would have the raw data. For the AC compressor I do not need CAN data as the control/regulation valve signal is a direct PWM pulse that changes in frequency to drive the valve (and thus compressor swashplate so the variable displacement) Of course that will only shows the control signal and not how fast the swashplate responds directly but I have ideas on that.

 

ADDITIONAL ALTERNATOR INFO:
Although I had previously checked the alternator one-way clutch and it was fine (there is a video of it above), I checked the alternator's load on the engine from Xentry in Nm.
Xentry always always shows around 12-15Nm at idle with no accessories powered on, both batteries new and fully charged, A/C set to low load, radiator fan is low around 40% pwm duty. This is a 180A alternator so ~2.5kW.
When A/C and blower is fully off it shows around 9-10Nm.
A/C fully on it goes up to 26Nm and I see it switch to charging voltage (14.4V) whereas it was at float (13.8V) or battery max (12.8V) before.
Tried turning on everything and idle went up to 800rpm from 660rpm and load went up to 29Nm and battery voltage went down to 12.2V (Alternator not enough and battery is supporting it and discharging)
Increasing rpms to around 2000 reduces the load a little but doesn't increase the voltage output.
Xentry names is "Calculated alternator torque" and it is a NEGATIVE number, so how much load it puts on the engine which basically gets subtracted from the engine torque produced.
I did some physics calculations, isn't the Nm above too much?
Correct me if I am wrong. The alternator pulley seems like it is less than half the radius of crank pulley. So it would turn more than twice the speed. A 180A alternator would produce around 3HP and at idle it would rotate at around 2000rpm. From power formula of Torque = 3HP / 2000RPM * 63025 = around 75 lb-in which would be less than 10Nm. That is at maximum load. Not sure how xentry calculates it but it seems excessive by like 3 times. Lack of documentation makes it difficult and there is no specified value range listed in xentry. Comments and corrections are welcome.

 

Checked the pressure sensor vs digital hvac manifold and I have seen when the engine and the AC is on car's pressure sensor consistently reading 25psi higher than the calibrated digital gauge on high side.
When the AC is off or system is equalized they read exactly the same. Since the pressure sensor is just after the compressor where high pressure gas enters the condenser while the high-side service port is after the condenser where high pressure liquid goes towards evaporator, I think the 25psi lower reading is normal so I think pressure sensor is fine. An off pressure sensor might cause adaptation issues or unload issues but not in this case, I think.
Scoping the control valve pulses next.

 

Sorry been traveling, but I think at this point, we may be going down the wormhole…
motor mounts look fine from your video. To me, the video clearly shows belt slipping due to compressor lock.

How does the new compressor feel when you try turn it by hand? Do you still have the old compressor? How does IT feel when you try to turn it by hand?
Compressors generally need a break in period. I’m thinking the compressor is eventually going to be the culprit. Either out of spec rebuild, perhaps too much oil. (Assuming you checked the system for debris too) Maybe rebuilt too tight initially and may loosen over time, though I wouldn’t personally chance it. (If you have the option to exchange it)

The fact that you had adaptation getting close, and now it’s not close means adaptation isn’t consistent either. Though it should be.
On top of that, AMG uses the same clutchless AC systems found on some Porsche/Audi vehicles.
Here’s a similar problem:
https://rennlist.com/forums/cayenne-...ock-noise.html

Just as @jmattioni has replaced his AC compressor with no issues, I’ve replaced AC compressor’s very similar to this design in the past, never had this outcome, ie needing adaptation. Strictly bolt in. So something is out of spec. (Not telling you something you don’t already know).

Very frustrating whenever things like this happen. Sorry this is happening.
I’ve lost count of how many times I’ve chased my tail due to out of spec, rebuilt “new” parts. It’s always tougher to diagnose newly replaced parts because we trust they’re within spec.

Keep us posted.

 

This is fairly normal, and how repairs typically go with this type of system. When everything is within spec. Adaptation is rarely needed….
They just don’t do well with out of tolerance stacking. Ie multiple parts of the system slightly out of specification or close to the edge.

What’s happening to OP is not common.

 

Thank you for you reply, I will be answering your questions below:
- I have the old compressor. Both feel exactly the same. I rotated the old compressor before I replaced it and it could easily be turned by hand. Feels similar to the hydraulic pump. But of course, it is the control valve (mercedes calls it regulation valve) that would make it stiffer as swashplate changes angle (varies displacement and builds pressure) so a hand turn would reveal only if it has obvious problems even when unloaded. There weren't.
- I added 30ml PAG46 unopened compressor oil after replacing the compressor and the drier (as WIS says 10+20) I am very careful about moisture and I don't even leave it without vacuum if I am not finishing it up the same day. I also open the drier package the moment I am putting it in. No exposure. About too much oil, I have none of the sysmptoms of too much oil, A/C cools very well, no weird compressor noises, no high-pressure or pressure cut-offs, no short cycling nothing. Although I am IT, I am also basic HVAC certified and check the temperatures from both the vents and Xentry, I do not believe there would be too much oil in it BUT if you know any reputable place in Miami that would flush the system and properly refill to specs for reasonable amount of money I would try it out just to rule it out.
- There was some very small spew outs during the initial control valve replacement I tried with the original compressor and it waw just green oil (UV dye I guess) and I didn't see any metal shavings. I didn't flush the whole system though BUT I checked the symptoms of clogged systems and I don't think anything is clogged.
- I got the compressor from authorized mercedes dealer and I am good with them but the labor in Miami heat (and the time of course) makes it prohibiting for me.
- All adaptations after the first one are quite bad. It square one right now, so basically only happened once.
- I checked all pulleys and belt alignments and they look OK, also nothing is obviously wobbling. One of the idler pulleys (the one just before the compressor, metal one) was going in-out very little so I replaced it but the new one was also the same, seems like it was designed that way and not really a bearing issue. Again genuine part from authorized dealer as I don't want to risk 3rd party with this one.
- I hear you, about chasing stuff out of spec, let me tell you one that I worked for 6 months! I also have a 2021 GLS 580 which has the 4 liter AMG engine without the twin scroll turbos and some minor differences, sounded like a serious exhaust leak, but crazy, you would be shocked if you saw the video. It did this when it was about 2 years old and less than 30.000 miles! I did exhaust leak testing, put cameras underneath the car, even checked turbo gaskets and everything towards front, looked inside the cats with borescopes and even replaced THE WHOLE exhaust and the MUFFLER with all AMG one and the noise was still there. I was close to selling the car AND IT TURNED OUT TO BE THE LIFT GATE! Whenever I was accelerating hard, the lift gate was VERY slightly opening, and a smaller than mm opening with the rubber was making a exhaust leak like noise. I readjusted the lift gate handle and that was it. I don't know what to say. At least the car now sounds exactly like a G-Wagen (actually better than the GLS63 because I am able to fully control the 3rd valve in the H-pipe and make it like the G63)
- I wrote before that I cannot rule out the possibility of both compressors having the same issue but I cannot only say it is non-zero but unlikely. My reasons would be, it is not the same part number, new part number is just a logistical replacement but still it means it came from a way newer car. Also my original compressor was only 64.000 miles (actually less than 60.000 when it started) it is quite a low number for a compressor to go bad. But of course such powerful belt slaps would quickly destroy or at least wear down everything quickly. So while you would be solving it, others would be following you with the same symptom. I consulted an authorized dealer foreman I know and this isn't something athorized dealers can fix anyway. Because, 1 they wouldn't spend that much time, 2 I already replaced almost everything which is their thing and 3, it would have cost as much as the car possibly.
- Yes, I do agree something is SERIOUSLY out of spec or there is some electrical stupidity. I will be posting the results of the scoping as removing the front sam seems pretty easy, like four screws. Although the wiring isn't clear because of the incorrect information in WIS I think I already found it.
- BTW, I did some more testing, as of now, the condition is pretty bad, I tested some manual actuations from Xentry. IMPORTANT INFO COMING: When it was this bad, it actually started chirping (very little) just after 5% commanded which is about 275mA out of 1000mA for the control valve, and goes progressively more towards 100%. We can't say it is the compressor doing this, it is very possible that this happens and the compressor happens to lock as it doesn't have a clutch and not a one-way clutch like the generator, nothing else is this heavy load. NOW THE IMPORTANT INFO:
Xentry has a page in A/C control unit where you can set the compressor load in 1% to 100% manually. It works well. THERE IS ANOTHER PAGE, where it says the engine control units request or something like that. It says THE ACTUATION IS PERFORMED WITH DECELERATION. But it doesn't seem to do anything? Rev downs or upshifts? What I mean is, when I command let's say 3% or some slow actuation to compressor valve from the A9 Refrigerant Compressor page, it directly affects the high-side pressure, compressor load and the chirp as expected. But the second page (screenshot below) doesn't do anything. I though it would apply THAT perfecnt actuation during deceleration. Maybe that's why I have the problem as I believe the car isn't unloading the compressor on time or at all during REVs doing down. The adaptation does affect that btw but if it is not calibrating properly then it is not going to work. BTW the third note in the screenshot basically means, if the engine needs cooling too, the fan may turn on even when A/C requests 0. But the deceleration part is important. I expected this to work when I did set it to 1% and the chirp would be gone temprorarily just like there is no chirp with 1% actuation from the A9 compressor page.
QUESTION: I have access to startek.info by subscription, official mercedes parts catalog, same as what the services see. I see there are other services as well. Is there a service that you can pay to ask the big guys at Mercedes? (not Services or dealers)

elaration

 

So this is interesting, let’s talk about the version of XENTRY you’re using. Is it the Passthru version? (Never mind, Screenshot shows Passthru) Are you using a C3 (or C4) multiplexer? Which one? Legit copy (obviously legit since you have subscription) which adapter are you using? The passthru version doesn’t have the same functionality. I’ve also found the later versions of XENTRY, say post 2015 (with a C4) are not as reliable on the older MB’s 2010-2014’s.
Also some of the pirated copies of XENTRY can also be unreliable. I had a friend that used a pirated version of XENTRY to run some seat adaptations after a seat motor replacement. He was unable to get the adaptation on the seat to “take”. Even though adaptation seemed to be going thru the motions. Kind of what you’re describing. It’s possible adaptation is being reset, but just isn’t being “written” correctly.

You’re correct about the dealer, these types of issues are a time suck and the dealer techs will be under pressure to “get it out the door”. I don’t believe this is a common issue. So they’ll be starting from square one again.

It’s been a while since I looked at startekinfo, but there were services only available to dealers, This may have changed as they update the site. But MB definitely has always wanted to maintain their service advantage over independents.


Good Luck

(edit). just to confirm we’re seeing the same things, this is what the actuation screen looks like on my older version of XENTRY running your VIN. Fairly similar. Also assuming you ran pertinent tests located in the testing tab?