Hi,

 

I have noticed since getting my 68 plate l&k from new that occasionally the ACC seems to have a glitch. I have found that when the car infront of me slows down the ACC kicks in, slows down then suddenly decides that the car infront has gone and begins to speed up again, this leads to me manually intervening. It is completely random and only happened a few times over the last 7.5k - has anyone experienced this?

Had this several times right through my ownership on my early (2015) UK build S3.  Every so often it would suddenly lose lock on the car ahead and accelerate!  The most frightening ones were whilst in stationary traffic as those required immediate and sharp braking to prevent me rear ending the still stationary car ahead.  I stopped trusting any of the systems after the third or fourth time.  Dealer could find no errors logged nor help with a diagnosis.

 

I also found that it would occasionally react to the car beyond the one directly ahead.  I can only guess that it’s something to do with the reflections seen by the radar being misinterpreted by the software.

I use ACC daily and have noticed a couple of things you need to keep an eye on. Firstly, in start-stop traffic if the car in front changes lane and the one in front of that is stationary, ACC will not always recognise it and I have to intervene and brake manually. The manual does give a badly worded warning to this effect. Secondly, some of the seemingly weird reactions it has are actually based on what is going on in the next lane to the right (I'm in the UK and it is the "undertaking" protection kicking in). If you treat it as an assistant, not the driver, it works brilliantly and I wouldn't go back to a car that doesn't have ACC.

I have noticed exactly the same, only rarely but a couple of times. Enough to make sure you keep a close eye on what its doing.

Proof that with today’s technology, fully autonomous cars are about as likely as flying cars. 

Only had the OP’s problem when the road is very twisty, eg on roundabouts. Never had i when the car in front is reasonably straight ahead.

On 11/03/2019 at 23:23, nicknorman said:

Only had the OP’s problem when the road is very twisty, eg on roundabouts. Never had i when the car in front is reasonably straight ahead.

ACC is not to be used on Twisty roads and Roundabouts. 

It is an aid on Dual carriageway and Motorway. I can't remember the exact wording in the manual. 

29 minutes ago, vfrvrs said:

ACC is not to be used on Twisty roads and Roundabouts. 

It is an aid on Dual carriageway and Motorway. I can't remember the exact wording in the manual. 

I have actually experienced the issues when the road is straight, going round my local bendy a-roads it is fine

On 13/03/2019 at 18:02, vfrvrs said:

ACC is not to be used on Twisty roads and Roundabouts. 

It is an aid on Dual carriageway and Motorway. I can't remember the exact wording in the manual. 

I know. But it’s not a hanging offence. I use it when I wish, knowing its limitations.

Use on motorway to be safest , set the distance to furthest scan , reduce when in slow traffic or the guy behind thinks your at it with the big gaps.

Like all software , hasn't been tested in all world conditions