vladarh

Hi guys,
I had a scary experience today. I got a new 2018 E350e a month ago.
Today I was driving in a queue, using Distronic at 10km/h, and a car in front turned off the road.
My car accelerated quickly and didn’t see a huge SUV in front of me. It was a big Merc GLE, not that hard to spot.
The day was clear, no rain, no fog…
So I barely had enough time to break. I stopped probably less than half a meter from it. I had to get on the break as hard as I could.
Has anyone else had something like that happening?
I think Distronic uses both a radar and cameras. It was able to see cyclists in the rain before. How could this happen now?
Anyway I made a call to the Merc customer service to have them check the car. I’m scared to use it now…

Egonvdv

never had this problem and I do use the system everywhere, even in town.
however it does sometimes brake later and harder than other time.. but it always brakes
but remember, it's an assist. You can never trust it blindly.

c4004matic

I had that issue on my C400. Its not exactly a "problem", its a system "limitation". That is why there are tons of of warnings on every page. I quote " the system is only an aid you must be aware of the traffic situation and maintain your hands on the steering wheel at all times".

nashvilletn

i always tell my clients to treat it as an assist, and to focus on using it on the interstate rather than city streets - for that exact reason.

Proeliator2001

Mercedes make a big deal about the system being great for traffic jams and working from a complete stop and most of the time it's brilliant at doing that. I engage it every single time I hit stop start traffic though I always keep an eye on traffic for sudden lane changers as it's not good at avoiding those. I've very occasionally had the same happen as op describes, usually a car turns off or quickly changes lane and my car speeds up before realising there is another car in front, only to have to brake hard.

As a work around, I set the adaptive cruise control speed limit low. If the stop/start traffic isn't getting above 20mph, I'll set cruise speed to 25mph. Means I keep up with flow but also means the car doesn't drop a gear and do full bore acceleration if it thinks there is a clear road ahead. Since doing that, I've had no heart attack moments. Previously, the speed used to be left at whatever I'd previously had it. So when the car misjudged a gap, it would think hey, I'm only doing 20mph but I need to be doing 70mph so would speed up quickly and keep accelerating till I smacked the brakes on.

chillysyrup

I think what happens is the system went into all clear mode when the car in front turned, then had a delay in recognizing the new vehicle. This has happened to me, and I felt I needed to respond with braking action and did not leave it to the Collision Prevention system to engage - although it may well have.

I recall reading that the system does not respond to slow or stationary objects as fast as we might like as it does not know if they are just roadway-adjacent features like signage, medians, buildings etc. that you may well come upon and then steer around (e.g. when going around a curve with a parked car at the side of the road). It works best with moving objects (which can only be one thing: other vehicles). It is reluctant to kick in with emergency braking and certainly has difficulty establishing a following routine behind objects it has not resolved as actual moving traffic.

vladarh

Of course, the system is just an assist. That's why I was ready to break and did so. It's just the issue that it wasn't assisting as it should. The collision prevention assist didn't even turn on (no beeps or braking). I had to break hard.
As far as I remember the speed was set previously at 70 km/h and I don't think I lowered that, so that's why it accelerated hard.
It's just strange that it was able to see even the smallest things before, and now it missed a huge SUV. But that's technology for you...
Anyway, just reminding everyone not to blindly trust the car

ua549

My only bad Distronic experience was when I was using cruise control at 45 mph. Distronic saw a 15 mph school zone sign and slammed on the brakes even though the school zonewas not active (no flashing yellow light). That first time the experience was startling to both me and the following cars. Now I turn off cruise control when nearing a school zone for safety reasons.

Proeliator2001

I've turned off the automatic speed limit change for a similar reason (mine reads the "limited to XX mph" speed signs fitted to some lorries over here causing me to brake hard from 80 to 50 or whatever they are limited to). At least yours was responding to a stationary speed limit sign not one going 50! Either way though, it is indeed surprising to following traffic.

gfmohn

Was the SUV stopped? When my 2015 C300 system has been tracking a moving vehicle, it will track it all the way to a stop (and then go again, etc.). It also seems to pick up stationary objects that come into its range. I assume it has been tracking them before they came into its danger zone. However, it does not do so until the last second. In your situation, the disappearance of the moving object it was tracking unmasked a new, stationary object (which I am assuming was stopped). I believe the sysyem treated this as part of the roadside environment, as chillysyrup describes. If the SUV was not stopped, I don't know what to say.

vladarh

I don't remember whether it was at complete standstill, but if not it was barely moving.
That explanation does make sense.