Pre-Safe Brake Oddity

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MB Enthusiast
Dec 11, 2009
E350 AMG Night Edition Premium Plus Saloon
Driving up the M1 in the early hours of Sunday morning. Not a car in sight on the particular stretch I was on. I had Distronic Plus on and set at 70 on the dot.

Then all of a sudden the Pre-Safe Brake warning came on and beeped a good 6 times, before the car backed off a little (or braked, not sure which), before it the sped back up and continued as normal.

It was a bit misty, but unless there was a ghost in the road it saw and I didn't, there was nothing in front of me to cause the system to activate.

I have had a couple of "Pre-Safe Brake Functions Limited" warnings over the last month or so, but having checked in the handbook I put it down to the fact on one occasion I was parked almost directly under a mobile phone mast, and the other I was parked nose-to-side with another car in a basement with hadrly a gap between.

Has anyone else experienced rogue activations?

It's a bit worrying I guess as the ultimate function of the Pre-Safe Brake is to effectively slam the brakes on, this could be very dangerous if traffic was following and there was no need to brake that hard!
Could it be you were close to one of the "restricted" areas, where Distronic will disable itself? The car will know via COMAND. There is a section in the handbook about this
I would have thought it would give me a warning to that effect though, and simply disable the system, not brake the car!

Been up and down the M1 a few times in the E350 and never had this before, so doubt it's that to be honest.
Yes, distronic will disengage and a warning will appear. This happens every time I have driven along the A5 near Nesscliffe.

The pre-safe on my car also has a tendency to beep erroneously under certain conditions. There are a couple of places on my route to work where it will beep once, in the same place. I suspect it might have something to do with RF interference from under road cabling or something similar.

What you describe sounds a little more disturbing, if the car did take unwarranted action I would want to get this checked out immediately, sounds very odd at best and potentially dangerous at worst.

Regards, Neil
Thanks. Will get it reported when I next go to the dealer then and they can check it out.
I've no science to support this but I've always imagined that the radar sensors could possibly reflect off a road sign, a countdown marker or even the central Armco on a bend or if you were changing lanes or even correcting within a lane so that the car is briefly facing the 'obstacle' head on. I presumed the system was clever enough to allow for such a circumstance, perhaps by referring to the steering angle.

I once had a warning on a particularly winding road in Surrey but eventually put it down to a metal gate or a 'sharp deviation' sign. Maybe I was being too forgiving and there is a fault since I've tried to recreate the scenario without success.

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