Pre-Safe Brake Oddity

[mbenz76]

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!

 

[whitenemesis]

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

 

[mbenz76]

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.

 

[elisetype25]

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

 

[mbenz76]

Thanks. Will get it reported when I next go to the dealer then and they can check it out.

 

[Toodeep]

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.