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I have a 2017 GLS550. Was salvage so no factory warranty
Drives perfectly except for 1 niggling problem. Every 6 seconds or so the RPM increases ever so slightly. You can feel a very slight bump as this happens
I thought it was the transmission so I changed the entire valve body. Just reassembled everything, road tested, and the problem is still there.
I checked the engine values in xentry and cannot see anything amiss. I am obviously missing something
I have a short video on the link below that shows the RPM move every 6 seconds
I changed the transmission thinking that was the cause. no difference.
No other errors in Xentry, I checked charge air cooler for leaks and vacuum for leaks, all seems fine. To me it feels it may be turbo related as it only does it under load. If you relax throttle a little, the 'blip' disappears. But I could be wrong, though, having changed transmission, I know know its definitely engine related.
From the description it sounds electronic. What was the pedigree of the replacement transmission? Are you sure it is trouble free? Why was the vehicle a salvage, a collision? One idea is to replace parts (modules, sensors) affected by the reason for salvage.
Vehicle was flood salvage. I fix them for a hobby.
I've fixed around 20 of them over the past 10 years, All range of problems from salt flood requiring engine change and just about every module, to broken conrods (due to hydrolocks) but mostly ECU changes which are usually straightforward
This one was a bit of a pain, new comand unit, electrical steering unit, starter motor, some new ignition coils 2 new fuel injectors, many AC stepper motors + blower motor
All errors are now gone in xentry, no error codes being thrown. I usually solve the rror codes as they appear, once they are all gone, car is usually perfect, but not in this case. The 'blip' is not enough to thrown an error code but its enough to drive you crazy when driving
not sure if its related to O2 sensor, they are showing OK in xentry
Today I installed new EVAP Sensor, sensors in each air filter, Boost pressure positioner and fuel system purge valve (circled in picture)
Still made no difference.
Would be so much more helpful if it would throw an error code to lead me in the right direction. One thing I did notice in Xentry whilst monitoring data is the engine speed jumps outside its specified range and turns red each time it 'blips' ie specified may be in the range 1250-1350 and it suddenly turn red and actual would go to 1401 for a split second then green again and back into the correct range
Next on my list is to change all the spark plugs and ignition coils, then if still no solution to change the charge air filter (including its sensors) and the fuel injectors)
Also the O2 sensors. I do have a donor engine sitting here that I am taking the parts off so its not costing a fortune,. just time and headaches. Car is running flawlessly apart from these tiny blips, very frustrating.
Is there a chance the transmission clutches are slipping? When the rpm blips, what sensation do you have in the vehicle? What is the status of the lockup clutch (removes torque converter at cruise speed)? Is there any possibility to measure hydraulic oil pressure at various points in the gearbox while driving?
You seem to to be taking a non-directed approach, and I suggest focusing in more closely on the reason for rpm blip. Need to gather data to be able to do this.
Is there a chance the transmission clutches are slipping? When the rpm blips, what sensation do you have in the vehicle? What is the status of the lockup clutch (removes torque converter at cruise speed)? Is there any possibility to measure hydraulic oil pressure at various points in the gearbox while driving?
You seem to to be taking a non-directed approach, and I suggest focusing in more closely on the reason for rpm blip. Need to gather data to be able to do this.
I dont think the clutches are slipping but I really have no idea. Sensation in the vehicle feels like when you are on a plane and a child in the seat behind gently kicks the back of your seat. Its very minor but very annoying. It happens approximately every 6 seconds when under average load, if I ease off slightly it goes away. I'm stumped because there are no error codes, usually I always have error codes to work through or to point me in the right direction.
I'm not sure if the problem is originating in the transmission itself, the torque converter, or the actual engine. I have posted a couple of videos below. The 1st is monitoring the torque converter, you can see its numbers jump into the hundreds at the 'blip' occurs. The 2nd video (bit shaky) is monitoring the engine RPM, you can see it turns red (outside the specified rage) as the blip occurs.
I don't have the skillset to interpret this data, am hoping someone on here will be able to help me narrow this down where to concentrate the search, (Engine, Torque Converter or Transmission)
Pay close attention to pages 6 and 30. Seems like the lockup clutch is either losing pressure (why?) or losing the signal to close (why?). Similar problem happened on my 8 speed Aisin box in a TDI Touareg, reason was old age at 238k miles.
Try a replacement torque converter as long as it includes a new lockup clutch. Or trace the sensors and wiring that tell the lockup clutch to close.
Interesting data. Did the blip happen during the videos? Hard to tell, it looks like all the values are pretty steady. I was surprised to see the torque converter "SLIPPING" during the video. What was vehicle speed and was cruise control used or manual throttle control?
The 9G-TRONIC document is pretty comprehensive. With that document, and your diagnostic system, you should be able to get to the bottom of it.
All of the symptoms you describe suggest malfunction in the lockup clutch function. Need to determine if this indeed is the problem, and whether the root cause is mechanical or electrical in nature.
Thanks for the response. Yes the 'blip' happened in both videos, in the engine one the RPM jumps outside specified range for a split second, in the transmission video, the TC slip speed goes from single digits to a few hundred, also for a split second.
It happens normal driving and on cruise control
After your help zeroing in on the TC clutch, I went into xentry and it lets you actually close the torque converter clutch to test it. I close it and, hey presto, it drove like a dream, not the slightest glitch. Went a few miles with it closed.
Am I safe to assume its definitely the torque converter now? If so will get it changed
Thanks again for the help, saved me from pointlessly swapping all those other engine parts :-)
Last edited by terrymargate; 03-23-2019 at 07:22 PM.
Reason: added pic
Interesting. Since you were able to command the lockup clutch to lock, and it worked, what do you conclude? I conclude the actuation system (software, sensor and valve) worked correctly, as did the lockup clutch itself.
Why would the lockup clutch open every 6 seconds? Seems like a flaky sensor somewhere.
There could be a flaky sensor somewhere that every 6 seconds gives an erroneous signal and the transmission thinks the lockup clutch should disengage.
Diagnose each of these sensors. If any of them were affected by flood damage, start with those/that one.
I have already checked many of the sensors, Nothing is ringing any alarm bells. Thats why I had started to change sensor and parts on the engine, thinking something there is throwing off the clutch controls
I have an extra element to add to this confusing mix. I have a 2017 S550 with identical transmission which runs fine so I took that out for a test drive with xentry hooked up.At cruising speed BOTH transmission controls seem to have the same data, they BOTH say OPEN for clutch status then SLIPPING as the vehicle accelerates and starts to cruise, neither of they say LOCKED.
I'm aware that something outside of the transmission can cause it to go haywire, I was on a trip from UK to Amsterdam a few years back in an S320, Car went into limp mode, Had internal speed sensor error. I reset it a few times and managed to make it back to the UK. Replaced ETC conductor plate (cost around $1000), then same error appeared within minutes. Turns out it was a flaky ABS sensor on the rear wheel was causing the false ETC error message. Costly lesson.
So back to this vehicle, I think the clutches are designed to slip to compensate for shift changes etc (it does blip changing into 4th and 5th each time as well as cruising). Just wish it would throw some kind of error code somewhere to help identify it.
I think in this case its one of 3 causes.
1) A sensor elsewhere in the engine, causing this mayhem
2) A fault on the transmission controller plate (though I would have expected this to throw a code if something was outside range)
3) A fault within the lockup clutch itself causing intermittent pressure loss (though this is not showing in Xentry)
Not sure which order to attack this in. Dont know how to really narrow it down. As for option 1, I may take out the working car and check all the sensors, reading etc, then do the same with the faulty one see if I can see any differences.
Option 2, it quite easy for me, but quite costly, around $900 for anew conductor place, easy to remove the valve body and swap them over, recode and activate etc.
Option 3, obviously the most labor intensive, remove and replace the entire transmission and swap the torque converter itself. I guess I'd try changing the controller before the converter, shame is they are TRP so locked to vehicle, wont be able to use it for anything else should it not turn out to be that
I guess common sense tells me to explore option 1 as much as possible to start with as I'd be kicking myself if I changed the TC and controller plate but it turned out to be engine related.
Strange development, I took it on a hundred mile trip the other day, (had xentry hooked up) towards approaching destination the 'blips' faded away and then stopped, I checked the fluid temp with xentryand it was 86 degrees. Was at destination for about an hour (fluid cooled), then coming home, same again, when fluid was nice and hot the 'blips' stopped again.
may do a complete fluid change again just in case this new lot still has some contamination. I have no idea how technical this lockup clutch is but it may be that the fluid has to be a certain viscosity for the clutch to work properly, which may explain how is improves when nice and hot. Worth a try at this point I guess
Contaminated fluid could affect performance. If the vehicle was flooded, could water be in the transmission?
Going back to the successful test where you commanded the lockup clutch to actuate, what does the latest observation indicate? What about the actuation components (solenoid, valve spool) that actuate the lockup clutch? Seems the clutch is losing hydraulic pressure periodically, every 6 seconds.
Have been helped by Jason at Autobahn Performance down in Ft Lauderdale. First he said it sounded like the controller plate. So I was making plans to replace that, then he spoke to a main dealer who said they thought the problem would be within the Torque Converter.
Of course its a PITA to change out the TC but if that is the problem, then at least I can get it solved
Found a local company to rebuild the TC for $295. Was about to pull the trigger on that, when the 2nd car I have with the same problem (s550 2017 convertible) suddenly flashed up message DO NOT CHANGE GEAR VISIT DEALER. Turned it it no longer goes into park. (but drives OK apart from the 'blip') Fortunately on the new 9g transmission, there is no expensive external shift module like on the 7g. The shift module on the 9g is an electronic actuator inside the transmission, easy to replace. So its either the actuator at fault or a problem on the controller plate. Have ordered another actuator (under $300) so will try that first
If that does not cure it, will replace the controller plate then at least I will know for sure if the 'blip' problem is coming from the plate or the TC before having to drop the transmission
Will post progress update on here as soon as I have one.
OK Its all solved at last. Big thank you to Jason Athenas at Autobahn Performance for all his help. He worked hard trying to nail down this problem, answered my emails late at night, made telephone calls trying to help us zero in on the cause.
We originally decided on having the Torque converter rebuilt. Then, once vehicle was in the shop, Jason raised concerns about having this done. We all know what PITA it is to remove and replace a transmission. What if the so called rebuild did not solve it? How would we know for sure if they had repaired the faulty component? If it was still faulty afterwards, do we trust they did it right and then go replace the whole transmission as that's all that would be left.
It was too many uncertainties, the only way to be sure we eliminated any converter problems was to install one from Mercedes, so thats what we did. Quite a bit more expense but more peace of mind.
Just picked the vehicle up, its driving perfectly. I'd have bet money at the outset on it not being the converter, I've fixed over 30 flood damaged cars now, many with transmission water intrusion and these are the first 2 that I've ever had with this problem. Strange they are both the 9g transmissions, perhaps Mercedes changed someone in the built process to make these more susceptible to water.
They are fixing the other car with identical problem next week.
I highly recommend the guys at Autobahn Performance. Nice to know there are still places that treat you fair and don't nail you to the wall. If you have a Mercedes headache that you cannot pin down and are in central or south Florida, give these guys a call. They are based on Oakland Pk, next to Ft Lauderdale. Telephone 954 771 5181.
Hope this thread helps someone experiencing problems with their 9g transmission.
12-24-2018, 08:43 PM
