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Does car need to be stationary when switching from C to S driving mode?

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2K views 29 replies 15 participants last post by  Rick_In_Tas  
#1 ·
I have an R172 SLK55 with three drive modes: C (Controlled Efficiency--that's what they call it for the AMG models), S (Sport), and M (Manual). In the manual, page 151, it states that the car needs to be "stationary" when switching to M using the program selector button. But it's never been very clear to me if the car needs to be at a complete stop when switching from C to S. The manual doesn't really state that.

To be safe, I've always made sure the car was stopped when switching to S mode. It's not a huge inconvenience, but I just want to get this nagging question out of the way for good :p
 
#4 ·
R171 '55 can switch on the move. W164 ML63 also btw. BUT when you change the mode it can change the current gear ; if you're in a gear at high rpm (e.g. 5000) without load (coasting, but at 5000 RPM) and you switch from S to C for example, or M to C (can't remember the cycle, should be C to S to M) then it will promptly change gear to a lower gear. So it's better to not switch when accelerating or braking hard.

Also if you're in 1st and go from M to C it will almost immediately go to 2nd gear.
 
R
#6 ·
Mine was a retrofit wheel. I've changed mode on the move with no ill effects. It's mentioned in the driver's manual too.

As @slk55inchina says, a prudent driver will switch wisely with the box in a stable condition. When going from an automatic mode to manual the box will select the appropriate ratio and this will be displayed on the instrument cluster. Similarly, going back to automatic the box will work out where it needs to be.

For drivers with RHS, the button is on the far side of the gear shift and it is inadvisable to change it while going into a tight corner or making a turn. In other words, anticipation is your friend!
 
#8 ·
Thanks for the info, guys. That's good to know that you can change drive modes on the fly.

I'm not sure if it's the same for the R171, but in my '14 55, the car will always default to C when you start the car regardless if you had it in S when you shut the engine off. I always like to get the engine and trans to near optimal operating temp before I switch to S. I'm pretty sure I read this somewhere about doing that, but I'm not sure if there's any advantage for doing that. In any case, I usually wait for an opportune time, such as at a stop light or stop sign, to switch from C to S so I can get the car roaring :p
 
R
#9 ·
I think that C mode cuts out 1st gear and also changes up a little sooner that S mode. So it's a little easier on the engine, which is why it makes sense to bring the engine up to optimum temperature before pushing it.

The reason it reverts to C mode is to improve fuel economy to comply with EU regulations. However, I have noticed that since the gearbox was coded to accept M (manual) and A (agile) mode it retains the mode that was last in use when the car was switched off. Before that, it would always revert to C mode.
 
R
#11 · (Edited)
Thanks, Robbie. My apologies if I have misled our AMG friends. We can only describe our experiences, but yes, you should ALWAYS check your vehicles manual.

Image


As you can see, there's no mention of stopping the car to move into M mode. In fact, I go from A to M when entering the exit slip lane from the local highway. The IC immediately shows "M" and indicates "7". Buy yes, always,always RTFM!!!
 
#12 ·
@Rick_In_Tas my comments were in reference to the original question, not your observations and experiences.

The manual describes you need to be stationary when moving between Auto modes and Manual, and not when switching modes. I read this as meaning you don't need to be stationary when switching between auto modes, E/C and S.

I have no idea as to why. The manual goes on to mention that there are controls to stop the gearbox and engine from being pushed beyond safe limits.
 
#14 ·
I’ve simply been amazed by the robustness of the gearbox and the intelligence of the software. It doesn’t seem to make any difference what I do to the thing it just works it out.
I don’t however have Manual mode and don’t know in what way that is different that using the gear lever or flappy paddles to change gear.
Also, if you haven’t had it done, I highly recommend getting A mode activated.
 
A
#16 ·
dirty hippy said:
I have an R172 SLK55 with three drive modes: C (Controlled Efficiency--that's what they call it for the AMG models), S (Sport), and M (Manual). In the manual, page 151, it states that the car needs to be "stationary" when switching to M using the program selector button. But it's never been very clear to me if the car needs to be at a complete stop when switching from C to S. The manual doesn't really state that.

To be safe, I've always made sure the car was stopped when switching to S mode. It's not a huge inconvenience, but I just want to get this nagging question out of the way for good :p
Click to expand...
17 cars in 36 yrs some with C,S,M and i switch at all speeds but never with the pedal to the metal.
 
A
#18 ·
C is all about fuel economy. The car - except more recent ones with 8 spd transmissions - starts is 2nd gear and shift points are at the higher end of the torque curve when in C. They also have a 2 spd reverse gear.
Since these trans are used around the world I very much doubt this has anything to do with European specifically.
 
R
#19 ·
dirty hippy said:
I have an R172 SLK55 with three drive modes: C (Controlled Efficiency--that's what they call it for the AMG models), S (Sport), and M (Manual). In the manual, page 151, it states that the car needs to be "stationary" when switching to M using the program selector button. But it's never been very clear to me if the car needs to be at a complete stop when switching from C to S. The manual doesn't really state that.

To be safe, I've always made sure the car was stopped when switching to S mode. It's not a huge inconvenience, but I just want to get this nagging question out of the way for good :p
Click to expand...
No you can change driving modes on the fly
 
#21 ·
For what it's worth I've switched modes while moving but not under load in other words when just cruising.
The button works in rotation so when you start in C one press takes you to S and another to M so another press is back to C which I've done on numerous occasions but now I'm concerned that I may have been doing the wrong thing.
I must mention that I've noticed that the ECO light doesn't come on and the cylinder deactivation no longer operates when I return to C after going through S and M unless I switch off and start again, so maybe we do need to be stationary before switching modes. Now I'm worried 😟.
 
R
#22 ·
I'm not familiar with 172s, and certainly not with 55's so what do I know? Ha, not a lot! However, from what I do know, the mode button for cars with paddles show C-S-M in a circular pattern, implying that, as you have demonstrated each push of the button gets you to the next model, i.e. if you are in "C" mode, one push of the button will get you to "S", the next push brings up "M" and then the next push completes the circle back to "C" mode. Round and round it goes, there's no other option but to proceed in that direction. That's what the label on the button implies too. You're not doing anything wrong.
As for Eco, I don't know about that at all, but it does sound as if changing gear mode does need to reset by switching off ignition. What does your manual say?
 
#23 ·
Based on my experience with the same car and 20000 miles of use, this is not the case, I've just changed when I want to, and my gearbox seems perfectly fine. I had it serviced last year and I could certainly tell the difference after that was done.
 
R
#30 ·
Totally agree with Alex. When I first got my flappy paddle wheel and got Agility mode programmed I was very aware that switching modes whilst underway could well cause a contention within the box, so my first use of M mode was very tentative!
 
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