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Discussion Starter #1
Was driving through a 50 zone on the M6 this week with the usual averaging cameras.

Road was too busy to use cruise control so switched to the speed limiter.

As I was changing to a slower lane with a Transit 2 inches off my rear the limiter suddenly deactivated and the car suddenly propelled forward hard (because my foot was pressing the accelerator quite a lot).

At first I thought the van had hit me but no, it was just the limiter deactivating.

Anyone had anything similar?
Or was it just a freak blip?

(Worth noting that unlike other limiters I've used, the Merc one doesn't let you override it by pressing the pedal to the floor)
 

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As I was changing to a slower lane with a Transit 2 inches off my rear the limiter suddenly deactivated and the car suddenly propelled forward hard (because my foot was pressing the accelerator quite a lot).

At first I thought the van had hit me but no, it was just the limiter deactivating.

Anyone had anything similar?
Or was it just a freak blip?

(Worth noting that unlike other limiters I've used, the Merc one doesn't let you override it by pressing the pedal to the floor)

Hi MotoPL, I have an Australian spec GLC250 Petrol. What you describe above is the "variable Speedtronic" function working as per design.
In my printed manual, page 187, it covers the usage of the speed limiting cruise control.
Paraphrased in my words..
If you depress the accelerator pedal beyond the kickdown point, the Speedtronic function is disabled (passive mode) and the vehicle will respond to driver input. Speedtronic function is regained once you come back down below your set speed

I suspect you were not aware that your 'extended throttle foot' was just at the kickdown point and the smallest movement put it over that threshold, causing the Speed Limit function to disable and allowing the vehicle to now respond to what is a large throttle input.

As I understand this, your last statement is not correct.

cheers
Phil
 

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Discussion Starter #3 (Edited)
Hmm, I'm completely aware of how a limiter usually works, I've had several on several different cars
My last statement is correct in terms of how the system is operating on my car - not really very helpful to be telling me my description of how my car operating is incorrect! I'm driving it, I should know!

I've tried several times to override it by pressing the pedal to the floor and nothing happens. And on this one occasion the pedal was only partially pressed.

Also, if i re-activate the limiter when my speed is too high, the limiter brings the speed back down - again, not a behaviour I would expect. Would expect it to have no effect until i manually lowered my speed below its setting.

Suspecting I have fault.
 

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I would have thought you last paragraph is how it should work, when you have set the speed you want the car to travel at whether you are below or above that speed it will take the car to that speed when activated.

It also says in the handbook: "If you depress the accelerator pedal beyond the pressure point (kickdown), speedtronic is switched to the passive mode. The multifunction display shows speedtronic suspended and you are able to exceed the stored speed.

It appears yours isn't working correctly.
 

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Discussion Starter #5
Thanks, yes appears that way... The majority of the time at any rate.

Will live with it till it needs to go in for a service or some issue.

Don't recall the suspended message appearing the display on the occasion it did work either.

Ho hum.
 

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Will see what happens with mine tomorrow, have never used it.
 

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My last statement is correct in terms of how the system is operating on my car - not really very helpful to be telling me my description of how my car operating is incorrect! I'm driving it, I should know!

I've tried several times to override it by pressing the pedal to the floor and nothing happens. And on this one occasion the pedal was only partially pressed.

Also, if i re-activate the limiter when my speed is too high, the limiter brings the speed back down - again, not a behaviour I would expect. Would expect it to have no effect until i manually lowered my speed below its setting.

Suspecting I have fault.
Hi MortoPL

Sorry for the mis-interpretation, I thought you were making a generalised comment about the Mercedes Speedtronic function and not your particular vehicle.

My intention is to clear up a misunderstanding not be argumentative.

Action of the Speed limiter function is as you stated, if selected when travelling at a higher speed than the selected speed the vehicle will decelerate back down to the selected speed. There is a warning about this in the manual, that it may be unexpected.

If you have engaged the speed limited function and can not force it into passive mode via heavy throttle pedal movement, this sounds like a fault. Have your dealer service department look at it.

I don't use this function a lot, but if memory serves, when I tried it last time, I was able to override the speed limit function. But as Philamg said, I will check it out again next time.

happy GLC'ing
 

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Discussion Starter #8
I'm suspecting a dodgy connection or something. The one time it did work was when it I changed lanes and rumbled over the cats eyes in the road for a couple of seconds... May have jolted something into operation.

Bit scary when it does it when not expected though. That 3.0 V6 has a **** of a kick!!!
Nearly propelled me into the car in front.
 

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Tried it out and definitely works with message speedtronic suspended appearing, must admit that you have to press the accelerator pedal a long way down to reach the kickdown point, didn't think it was working at first.
 

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OK, took the GLC out for a brief drive this afternoon.

Checked out the Speedtronic Speed limit function.
- Engage when travelling below set speed, accelerate up to set speed and it ceases to accelerate past set speed.
- Engage when travelling above the set speed, it applied the brakes, not hard but not gentle either until speed drops to set speed.
- To force the kick-down action, and cause Speedtronic to go to 'passive' mode, the accelerator pedal has to be hard pressed to the floor. Any amount of pedal modulation before you hit the floor does nothing. There is a small notch at the last bit of travel, right at the floor, it's like pressing through a switch gate...once you do that the vehicle will accelerate hard.

This is all as per the instruction manual.

MotorPL, check you kick down function again ...the first time I tried it, I was gently advancing the pedal to the floor ...I though it was at the full extension, but it had just rested on that last notch in the travel, a heavier press gets you through that and she takes off!! On a rough road, you may not be aware of that last little bit.
 

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Agree Citizen, the kickdown is much further down than I expected, I suppose it is designed that way to stop it being pressed accidentally.
Will be interested to see if Motos works or he has a fault.
 

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Discussion Starter #12
Thanks, I'll try that - maybe I didn't push it as hard as needed. Certainly don't remember pushing past a 'notch'(... but then that wouldn't explain why is went passive in the middle of changing lanes when I didn't really move my foot at all)I'll let you know in due course - but it's biking weather at the moment so my GLC is having a rest for a few days!
 
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You will definitely know if you had pushed past the kickdown, a solid stop before and then a good push to pass it.
 
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Discussion Starter #14
OK, so finally got around to testing this thing out again. And yes, the override does work.

There's a definite 'click' from the pedal at floor level, the display shows 'Passive' and the speed picks up.

So, going back to the original scenario I described where it de-activated unexpectedly...

I can say with 100% confidence that I didn't press the pedal that hard, and the display definitely didn't display 'Passive'.
(I remember looking at the display cause I was worried about my speed when it shot up when I was in the 50mph averaging zone)

So, guessing something isn't right, but no point taking it in the garage 'cause its not repeatable - hopefully just a one off glitch.
 

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Hi MotoPL,

Is good that you were able to verify Speed limit override function.

Just re-read your original post....assuming you were about to or were in the process of changing lanes, making a move to the left, I guess, ...any chance you might have inadvertently knocked the Cruise Control stalk away from you when you moved the indicator stalk to the left (downwards) ??? ...as this would have disconnected the Speed limit function, and if at the same time you had more throttle than required .........

...if not, then this does leave some doubt in the operation of your Distronic Speed Limit. ..which is somewhat worrying.
Even a bit more worrying, if you can not reliably repeat the fault, as then you don't know when it might occur.

..hopefully you have no repeat performance!!

Happy and safe GLC'ing
Phil.
 

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Discussion Starter #16
Definitely didn't catch the stalk because the limiter activated again once the speed came back down.

Slightly off topic...
The number of times i've done the opposite though - gone to tweak my cruise control or speed limiter speed and ended up indicating!!
Crazy place for the speed limiter stalk though, hidden out of sight behind the steering wheel - can't even see the light on it to see what mode it's in - can see why the facelifted version appears to have the controls on the steering wheel itself.
 

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- gone to tweak my cruise control or speed limiter speed and ended up indicating!!
Crazy place for the speed limiter stalk though, hidden out of sight behind the steering wheel - can't even see the light on it to see what mode it's in - can see why the facelifted version appears to have the controls on the steering wheel itself.
LOL ...been there done that.!!

Must admit though I am getting used to finding the stalk without looking. (mostly...lol).

And same here , with my standard seating position, that little indicator light for the speed-limit function is hidden most of the time behind the spoke of the wheel. It's good to have it noted on the HUD ...if you have that option.

Apparently, the Cruise control stalk, has been a MB 'signature feature' for some many years. So it is interesting that they have moved to a wheel button system. Would like to know the amount of 'testing' done on the ergonomics of this set-up and if it leads to people taking their eyes off the road momentarily. Does the new MBUX system respond to voice command to "increase cruise Speed" and the like?? Vehicle manufactures are doing a lot of research in to the man/machine interface .it is interesting times!!
 
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