2021 e-450 adaptive cruise control

[jimdh56]

My 2021 e-450 comes with adaptive cruise control. I turn this off, but it is always on. This is a big safety issue for me because if I am going down the highway at 80mph in an 80 zone and the speed limit goes down, the car slows quickly to the new speed limit. This is not as bad as when it also picks up exit speed limits at times. Then you are slowing from 80 to 45 quickly and the speed limit has not changed. I have talked to my dealer who is clueless (When I asked if they report this type of stuff to Mercedes, he gave me the US Mercedes number (which does not reply to e-mail or voice messages). Any ideas?

 

[Ron240]

This will be the Active Speed Limit Assist part of the Driving Assistance Package that you are talking about which will operate in conjunction with the cruise control.
I really would have thought it was possible to turn off this additional feature...so are you absolutely positive it cannot be diabled somewhere in the settings?
I am assuming you are not in the UK because we do not have an 80mph speed limit...our national maximum is 70mph.

Mercedes offer this optional Driving Assistance Package at significant cost (at least £1500 depending on model) which includes multiple features, but the only one I would actually want is the Active Distance Assist, which other manufacturers call Adaptive Cruise Control.

 

[jimdh56]

I am in Utah, USA. There is an option to turn on/off the Active Speed Limit Assist, but even with it off, it still adapts. Hoping for a software update.

 

[Ron240]

There is an option to turn on/off the Active Speed Limit Assist, but even with it off, it still adapts.

This seems very strange because this is the feature that you are having the issue with...so it cannot actually be turning off in that case.
Maybe other members here that have the Driving Assistance Package on their car can comment on this.

It is interesting to know that parts of the US have an 80mph speed limit...I was not aware of this and always believed you had the same or lower limits than the UK.
Having just checked I see that the maximum speed limit in the country is on the Texas State Highway at 85mph.

 

[Botus]

My 2021 e-450 comes with adaptive cruise control. I turn this off, but it is always on. This is a big safety issue for me because if I am going down the highway at 80mph in an 80 zone and the speed limit goes down, the car slows quickly to the new speed limit. This is not as bad as when it also picks up exit speed limits at times. Then you are slowing from 80 to 45 quickly and the speed limit has not changed. I have talked to my dealer who is clueless (When I asked if they report this type of stuff to Mercedes, he gave me the US Mercedes number (which does not reply to e-mail or voice messages). Any ideas?

legally they can't in today's world be seen to be driving above a new speed limit - it would be great if it could see it earlier and reduce speed more progressively, but its sign recognition - but imagine it this way - if plod is in a mood or indeed an always on camera is nicking every idiot that hasn't got to the posted limit (just like the law suggest they should) I'm sure 200 quid and 3 points saved would make your day just because your car is sensible to helping whilst you're asleep

if it offends, can you not just turn off the speed limit assist feature, and hope you're paying attention come the roadworks

 

[Botus]

This seems very strange because this is the feature that you are having the issue with...so it cannot actually be turning off in that case.
Maybe other members here that have the Driving Assistance Package on their car can comment on this.

It is interesting to know that parts of the US have an 80mph speed limit...I was not aware of this and always believed you had the same or lower limits than the UK.
Having just checked I see that the maximum speed limit in the country is on the Texas State Highway at 85mph.

wow its been quite a few years since they went back to normal most are faster than ours now

Speed: Maximum posted speed limits

Speed: Maximum posted speed limits

www.iihs.org

 

[Botus]

I am in Utah, USA. There is an option to turn on/off the Active Speed Limit Assist, but even with it off, it still adapts. Hoping for a software update.

is there an overall speed limit in play (that maybe you can get at - and its set low)
and then the speed limit assist bit?

of course it will always adapt to the idiot in-front - if lower than your set speed - note in case you've not found it - the gap is adjustable (to a minimum of 2 second rule - which will seem close till you trust its competence and or its raining and the driver should build in a bit more safety by setting it to 3 seconds or whatever)

on mine its level of road rage changes with the suspension / gearbox setting
C = asleep vague wandering elastic band
S = full on road rage, needless gear changing and wasting petrol

 

[Ron240]

Botus... I am trying to figure out the way you are thinking in realtion to the OP's specific issue because I believe I have already addressed it.
It is not the commonly referred to "adaptive cruise control" (Mercedes call it Active Distance Assist) that is the problem here, but where the car automatically adjusts its speed when seeing a different speed limit sign while the cruise control is operating.
Mercedes call this feature Active Speed Limit Assist and the OP has stated that there is an option in the settings to turn this off...but when turned off he states "but even with it off, it still adapts"
I took this to mean that the car is still adjusting speed when seeing road signs with a different limit while using cruise control.
This makes no sense to me because why is there an option to disable Active Speed Limit Assist if it carries on working exactly as before?

To the Original Poster...it is possible that when turning off Active Speed Limit Assist it only remains off for the current ignition cycle and will be turned on again by default next time. This is what hapens with the Active Lane Keeping Assist on my car.

 

[Botus]

Ron, I saw and read all the points you again mention in your first 3 sentences above. NOTE I have used grown up acronyms and naming conventions that should be industry std not some marketing clap trap, unique to each manu.

I have ACC (active cruise) and know how it works I've had on my last two cars. I also understand what speed limit assist does - track the signs and puts the brakes on - usually when you don't want it

The OP says he turned off speed limit assist but it still functions - that is unlikely. Yes, the USA is a nanny state and might have other legislation and software but its unlikely. Far more likely and this is what I'm trying to get across (and it seemed abundantly clear to me in what I wrote previously)... OTHER safety features are in play and in casual use appear to have a similar effect to speed limit assist (and so the OP thinks it wasn't really disabled by the user in a way he believes it should when off).

A few culprits that seem very likely are on the car and can allow the car to alter the speed away from the one the driver set out to drive

1) ACC picking up distant vehicles and reacting to them. On a BMW they default to the 3 second rule, but on my Merc it stays wherever I set it last... so if I have on the 5 second rule its looking 1/2 mile away and backing off for people way out in front

2) I can imagine in USA it might have a speed limiting function enabled and is this coming in to play regardless of any other settings - and or - its been turned on in error. Goodness knows why its there, its irritating and dangerous for zero benefit if the car has cruise control anyway

3) Traffic safety - the bumper saving low speed always on version of ACC. Often overly sensitive and picks up noise in the driving environment and occasionally will stand on the brakes when there is nothing there

 

[jimdh56]

Thanks for the discussion, but the issue is while driving down the road with cruise on, it often picks up the speed limit from the exit and slows a lot. Nothing to do with the driver in front of me.

 

[Botus]

Thanks for the discussion, but the issue is while driving down the road with cruise on, it often picks up the speed limit from the exit and slows a lot. Nothing to do with the driver in front of me.

not sure I get that terminology, "picks up the speed limit from the exit"

I found this on another forum for Mercs,

So a starting point would be to ensure the latest Sat Nav mapping is installed (in case some limits were recently updated) as the speed assist works to the following logic based on 3 steps;

1. Null (No knowledge)
2. Navigation (Installed on the HDD)
3. Camera (Reads roadsigns)

Reading the marketing blurb, it should show the speed limit from the satnav map data but adjusts if it sees a sign to the contrary.

If the camera hasn't seen a repeater sign after a time the speed symbol goes off or shows the wrong speed.

OR
Not all roads have speed signs on them and UK law takes care of this by defaulting every road limit without signage to 30mph.

OR
The only time it reliably fails is it reads "70" as "10" in one sign near my house. Granted the "70" is pasted on and looks home-made by some tradie so it's understandable

OR
Pretty accurate to date with speed limit indications, barring the occasional failure to recognise filthy, overgrown or damaged signs

OR
Picked up the speed signs written on the side of buses or lorry's, etc

OR
Most of the time the issues come about after passing a de-restriction sign, the de-restriction sign then shows on the dash for a short while, after it goes out there is often no sign on the dash or if there is an incorrect speed sign will show. There are a couple of examples near my house, 70mph will show on a single carridgeway or on one road 30mph where it is 60mph

 

[keefysher]

Thanks for the discussion, but the issue is while driving down the road with cruise on, it often picks up the speed limit from the exit and slows a lot. Nothing to do with the driver in front of me.

The camera system may need re-calibrating.
Is the camera lens clean? Often there can be a build up of dust on/between the windscreen (windshield in US) and lens.
Have you had a new windscreen?
Do you Intelligent Light System? Do the headlights work OK or are they random, which may also be due to calibration.
Do you have Traffic Sign assist activated, can be switched off by turning cruise control end switch by rotating. I turn mine off as it picks up signs on side roads, junctions etc. Too sensitive.

 

[daveenty]

It sounds like it's picking up/reading the wrong sign, i.e. one adjacent to the road which you're actually on. I've had it a couple of times, especially when exiting one road to enter another, both 60 (example) and it sees a side road signed 30 or 40 and tries to drop down to that speed by harsh braking.

All I do is to dab the brake or hit the switch to cancel the cruise but it's not a pleasant experience to be honest.

 

[Ron240]

It sounds like it's picking up/reading the wrong sign, i.e. one adjacent to the road which you're actually on. I've had it a couple of times, especially when exiting one road to enter another, both 60 (example) and it sees a side road signed 30 or 40 and tries to drop down to that speed by harsh braking.

All I do is to dab the brake or hit the switch to cancel the cruise but it's not a pleasant experience to be honest.

This is the same issue the OP is having.
What about disabling the Active Speed Limit Assist because it should prevent this issue from happening?
Is it like some of the other safety systems and on by default every time the engine is started?

 

[daveenty]

This is the same issue the OP is having.

Which is why I replied...

What about disabling the Active Speed Limit Assist because it should prevent this issue from happening?
Is it like some of the other safety systems and on by default every time the engine is started?

Active Speed Limit Assist is not an individual function and forms part of the whole Distronic experience. The only way to disable it, as far as I can make out, is not to set the Distronic, or cancel it when leaving the motorway. Mine only gets used on motorways though even then you have to be aware that it will brake for you, sometimes quite severely, when a change of speed limits happens such as road works etc.

 

[Ron240]

Which is why I replied...

Fair enough....
It's just that you started your post with "It sounds like it's picking up/reading the wrong sign", which is exactly what the OP said it was doing so I wasn't clear on whether you were sure or not.

I asked the question earlier about disabling the Active Speed Limit Assist and the OP said it could be turned off but the issue remained exactly the same...which I found very strange.

I think we can all agree the system has its limitations and does not always operate in an ideal and logical way.

 

[jimdh56]

The camera system may need re-calibrating.
Is the camera lens clean? Often there can be a build up of dust on/between the windscreen (windshield in US) and lens.
Have you had a new windscreen?
Do you Intelligent Light System? Do the headlights work OK or are they random, which may also be due to calibration.
Do you have Traffic Sign assist activated, can be switched off by turning cruise control end switch by rotating. I turn mine off as it picks up signs on side roads, junctions etc. Too sensitive.

The camera is clean (all of them). The car is rather new (now with 10k miles) and the issue has been happening since I bought it. No new windscreen. The headlights work as expected. I will try turning off Traffic Sign assist. Thanks!!