This morning I found my GLC 300 won't change gear to 9th gear and stay in 7th gear in the ECO mode at 70 mph. If you change to normal mode and it will change to 9th gear immediately.
When 9th gear in the normal mode and changed to ECO mode and it will stay in 9th gear but if you stop and speed up to 70mph in ECO mode and it will stay in 7th gear again and won't change to 9th gear.
Anyone has this problem or only my GLC?
thank for the input

And your "problem" is ? ECO is mis-expressed to the customer by 99% of the MB dealers/salespeople out there ... the German's programmed ECO as their Autobahn setting - primarily to adjust the steering ratio - and if you ever have driven on the Autobahn with a German (preferably at night) - yep they will "ride" in 7th gear, not 9th..

Mine changes to 8 and 9 in Eco.

The Mercedes 9-speed has a 9.17:1 ratio transmission that barely revs the engine (1,350 rpm) at highway cruising speed. At that speed, the engine is maxed out with no surplus for acceleration without downshifting while cruising; therefore, downshifts occur with nearly every pressing down of the accelerator.

If you’re not using cruise control and if you tend to work the accelerator while cruising, the transmission may want to stay in 7th gear. However, in “Eco” mode if you set your cruise control at 70 or 74 (as I do where I can), the transmission should shift from 7th to 9th. But, I think in “Sport” the transmission stays in 7th gear.

You can also upshift to a higher gear using the shift paddles, but I haven’t experimented with this much at cruising speed.

This just started happening to my 2017 GLC - I had a 2016 GLC before that always up-shifted - so I noticed right away when my 2017 did not up-shift past 7 while on the highway. I noticed this started happening on cold days. Recently in NJ we had days of 3 degrees and on those days it would not go past 7th gear in Eco Mode unless I manually up-shifted with the paddles or switched to Comfort Mode which shifted without issue to 9 immediately. Took it to the dealer for a look see and they tested other GLCs that did the same thing. So this looks to be cold weather related and something new in the programming, as I said my 2016 never did this and I had one of the first in the US.

Have you tried a gearbox reset to see if it changes this behaviour?

Your gearbox 'learns' from your style of driving and can adapt to suit. Sometimes it 'learns' bad habits!
The reset returns it to factory settings.
Search to find exactly how to do it.....
Something like... turn ignition on without starting engine, press accelerator all way down and hold for 30 seconds and release.
It's a simple procedure but I can't recall exactly what it is.

Did anyone ever get a resolution for this issue? We are having the same issue and the dealer service tech can't find anything wrong.

I have this issue also (2016 GLC 300) and have taken it to the dealer a few times to try and diagnosis and fix. I first noticed the issue happening after a software update the dealer performed. I took the car back to the dealer and their tech said it was "normal." I of course said it was absolutely NOT normal and told the tech exactly what to do to replicate the issue (start car, change dynamic mode to Eco, drive car...then observe it will not shift into 8/9th gear unless you manually upshift using the paddles or change it back to comfort. They were able to replicate the problem and told me they would have to keep the car for a few days to gather "data" to send to Mercedes. My last contact with the dealer was in September and my service adviser said they have not heard back yet from Germany and would follow up with them again.

Oh, and I've done the "transmission reset" procedure several times and it didn't help.

Thank you for the reply. We are frustrated by the dealer being "unable to replicate the issue". I am glad the dealer did not tell us it was normal as well as that would have gotten them lit up verbally. They sent our code off to the tech and we too are awaiting a resolution. Frustrating that such a nice vehicle has these issues. Hopefully we can get this resolved...

We have an '18 4M and it shifts into 9th when in Eco. It also stops the engine when coasting downhill; I can feel it kick on slightly and noticed the revs rise again when it loses enough speed or I press on the gas pedal.

it seems to be that the engine goes into 9th less with E compared to C, which is odd to me.. for E to go into 9th or even 8th sometimes it has to be a well warmed-up engine.

in E though when not pressing the accelerator, the D turns green and i assume this means it goes into neutral?

My '18 has done this during the first few minutes of highway driving since new. It goes into 8th and 9th after a while. I use the paddle when I want to upshift sooner. Not an issue IMO. They all do it and it goes away after a bit.

My recommendation is tofocus on enjoying an awesome car that few people can afford and shift manually if you want 8th or 9th gear sooner. Forcing my SA to listen to my personal view of how MB "should have" designed my luxury car does nothing to improve the world I live in. MB says it's normal. If this ruins the ownership experience for me, I'll drive something else or put a post-it note over the tachometer.

In addition to engine conditions - it also has to do with "head wind" - will not auto shift up to 8-9 when encountering added head-wind and higher the speed the greater the head-wind effect (which we don't notice inside the cabin) - with no-wind - or even better tail-wind "zip" it will go all the way up EZ

Australian GCL250 (similar to GLC300 in US)

Have noticed that when in ECO mode the transmission is less likely to change up to 9th gear, it will hold 8th for a longer period or up to a higher speed ...over 110 Km/h . when compared to "comfort mode"
It will change up to 9th, but is more likely to change back to 8th if a slight incline is approached.

The key to this behaviour is fuel consumption. ..you need to be on a level road for some distance and no variation in wind velocity ...but I have noticed that at given speed ..say 105Km/h ..in 8th gear ..the fuel consumption is just slightly lower than in 9th gear. You also get the coasting behaviour in ECO, where the transmission disconnects from the engine to allow the vehicle to roll freely without drag from the engine. Usually on downhill grades. You will see the engine revs drop to idle. This will not occur in the other driving modes
The differences in fuel usage are probably pretty marginal given all the other variables ...however I suspect there is a fuel saving to be had.
Hence "Economy mode"

Mine does too. When engine has warmed up it shifts to 9 around 101 km/h, when cold I have to increase speed to 130 km/h to have the car shift up to 9th in ECO mode. Something else I noticed, when the engine starts to shift to 9th at 101 km/h when I then switch to Comfort mode and let go of the gas completely the fuel consumption is not going to zero as I would think and as it does when the engine is cold. So less engine braking when engine is warm. Also the fuel consumption seems to rise at the same speed and road conditions from then on. Same for you as well?

have any of you with this issue compared real time mpg when in 7th vs 9th gear. as others have said, it might actually be more efficient in 7th at times when there is load.

The MPG shown at the BC is worse in 7th gear than in 9th. I put it in 9 by manual shift and fuel consumption decreases, when the car downshifts to 7 whilst driving constant speed, I notice mpg is getting worse.

My 2018 does this too.

The main concern that I have with the vehicle's behavior is that when "gliding" initiates, the transmission stays in 7th gear. What happens after "gliding" mode ends is that the car jerks on highway speeds when transmission couples again. If it would shift up to 9th gear, you would not get that jerky movement as gliding mode is ended. Going from 700s rpm to over 2000 rpm (because it is still in 7th gear) at highway speed does not sound and feel right to me.

Not sure if I was able to explain it correctly.

My 2020 GLC300 RWD does not do what you describe. Since I live in a rural location where roads are mostly flat, cruising speed is between 55 and 75. I set the ECO mode immediately and turn the cruise on at 55+ mph. As long as I am close to level, my GLC always goes to 9th and only gears down for acceleration or inclines. After 47,000 miles, with Michelin Defenders set to 32 psi, my lifetime mpg is still 30.4. If you can't get to ninth in Eco mode on a level road at 55+ speeds, I suggest seeing a dealer.
FWIW, I tried driving around in S mode and noticed the car would not go in to 9th willingly. S mode is one click Forward with the roller switch and ECO mode is one click Aft. Just sayin'

This doesn’t happen on Comfort mode at all. As soon as C mode is switched (from E mode, when it is stuck at 7th gear), C mode makes transmission upshift to 8>9 right away, when on same exact speed.

The other day, I was around 78mph on Eco mode, the transmission was insistent to be on 7th gear on a very flat highway. I had to manually gear up to 8th and it continued to 9th after that. Very strange.

If I am not misunderstanding, earlier posts above mentions the same behavior was on all other vehicles of the same year, as the dealer tested. Guessing some common programming issue, or perhaps a logic behind that I can’t figure out.

ps: Very confident I am on E and not the S. Impossible to not notice the change in the feeling either 🙂

For future reference; Happy to update that the issue is completely gone. Eco mode immediately upshifts to 8th and 9th gear on all conditions now. I have done nothing else but only this, and after completing the steps, I noticed the Eco mode shifting freely to higher gears on my very first drive. Even got a 34mpg on the same exact commute that I have been always getting 29-30mpg.

What fixed it was the controversial “transmission reset” procedure. I have always thought that to be nonsensical, however, first hand experience that it fixed the issue that I have been having for a long time.

Not sure exactly what that procedure does, but it did whatever it has done to revert back to the original, expected condition.

Please see my other post here
https://mbworld.org/forums/glc-class...ml#post8859124

I was going to ask how aggressive you had been driving in the day or two prior to your complaint.

I like the ability of the transmission to learn driving habits, my complaint with Mercedes transmissions is that they are slow to forget that time you had to merge or pass.