Unexplained ACC braking

[Amarillo]

This has been mentioned in my tour blog, but I think it deserves its own thread.

I was recently driving along a provincial road in Romania, the DN13 between Brașov and Feldioara. My adaptive cruise control was set to 80 kph, and I had a clear road ahead.

Without apparent explanation the vehicle braked accompanied by and audial and visual warning to brake. I tapped the accelerator which cancelled the warnings and the braking and we continued without incident.

On return to our campsite I cleaned the radar (and the rest of the car except wheels).

Three days later we were driving along the same section of road, this time following a car ahead at about 75 kph. At approximately or exactly the same spot the brakes were applied accompanied by an audial and visual warning to brake. We were, at that time, being overtaken by another car, and it is that which may have triggered the braking.

I have written to VW about this and have had this near worthless response.
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Thank you for contacting Volkswagen Commercial Vehicles UK.

I am sorry to hear of the issues you have been having with your vehicle.

There are no known faults on your vehicle relating to the emergency braking system. I have spoken to our Technical Support Team and they have advised the emergency braking system is connected to the adaptive cruise control and the way it is activated is, if something obstructs the camera on the front of the vehicle. They also advised it can be triggered by railway lines if they are next to the road and come into the cameras view.

I hope this information proves useful. Thank you for contacting Volkswagen Commercial Vehicles UK.
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There is no railway along that section of the DN13.

Is it worth trying to get to the bottom of this mysterious and worrying incident given that I'm unlikely to drive that section of the DN13 ever again?


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[Annik]

Russian retaliation?

 

[Ocean Spirit]

At the end of the day, there is no intelligence in the emergency braking/ACC radar function.
If it picks something up it's going to activate. As picking something up doesn't equate to a fault we are stuck with that limitation.
I have seen reports of 'unexplained braking' on the web but mainly based on the emergency city braking rather than ACC and I'd hazard a guess that with enough time spent each and every case could have the trigger explained.
How dangerous could it be is the real question.
In normal conditions I suspect it's shock value with a tinge of annoyance but in icy conditions perhaps the problem could be worse? but then your driving style is likely to differ enough to avoid the automatic braking.

So whatever your radar has picked up I'd assume it would continue to do so but equally I wouldn't worry about trying to get to the bottom of it.
This used to bother me (2 minutes in)
https://www.plymouthherald.co.uk/news/local-news/volkswagen-car-keeps-thinking-its-689355

 

[CampervanTime]

I found the same system on my old Audi S3 used to have a few 'moments'.

Usually when pressing on along a bumpy road and it got surprised by rapidly approaching tarmac or road signs etc. Was very infrequent but it did occasionally false alarm.

Just be thankful you don't like in the same road as this poor chap in Cornwall!!

https://www.cornwalllive.com/news/cornwall-news/vw-tiguan-automatic-braking-problem-658847

 

[Stoneybroke]

The basic tech is a form of radar. Radar can be fooled by various objects, normally where there is some movement or vibration.
A handheld Home Office approved radar speedgun used to be checked before and after a session by pointing it at a tuning fork, which, when vibrating, equates to a particular speed - even though the operator is holding it in their hand.
It could be the wheels on the passing vehicle had a similar effect, fooling the radar, or some roadside object...
Unnerving though.

 

[CampervanTime]

I’ve got a camera based adaptive cruise system in my BMW i3 and it’s utter rubbish. The radar system is far better but it does make you wonder if they need a combination of both in the future

 

[WelshGas]

I’ve got a camera based adaptive cruise system in my BMW i3 and it’s utter rubbish. The radar system is far better but it does make you wonder if they need a combination of both in the future

Or better still, standard cruise control and an attentive driver.

 

[SimonB]

I’ve got a camera based adaptive cruise system in my BMW i3 and it’s utter rubbish. The radar system is far better but it does make you wonder if they need a combination of both in the future

It could be interesting to go along that road in a number of VW vehicles with ACC and see if they all brake at the same place with no obvious reason, or is it down to some individual feature or setting.