My adaptive cruise has started seeing problems (on motorways) that don't exist.

 

When passing a exit slip road it will often decide that I've taken the exit and apply the brakes as if I'm about to come to the end of the slip.

 

Doesn't happen at all junctions - maybe 20% of them.

 

I know that a little pictorial diagram does pop up a few moments before the braking but it's pure chance that I might spot it as it's only on screen for 3 seconds or so.

 

Anyone else experienced this?

Not something I’ve had. Perhaps the radar needs recalibration? Have you had a front end bump? 

This will happen if there is only one car in front of you and it takes the slip road then slows down. The radar has no way of knowing that the motorway continues straight ahead and can only assume that  you will follow the car that turned off. If it can see another car ahead on the motorway then it knows it can continue straight.

49 minutes ago, D402 said:

This will happen if there is only one car in front of you and it takes the slip road then slows down. The radar has no way of knowing that the motorway continues straight ahead and can only assume that  you will follow the car that turned off. If it can see another car ahead on the motorway then it knows it can continue straight.

I get that on any road where the car in front peels off to the left - this motorway quirk is something different.

1 hour ago, Berisford said:

I get that on any road where the car in front peels off to the left - this motorway quirk is something different.

Ok, can you be more specific about the circumstances, particularly what vehicles in front of you are doing? I've worked on these systems so might be able to provide an explanation.

2 hours ago, D402 said:

Ok, can you be more specific about the circumstances, particularly what vehicles in front of you are doing? I've worked on these systems so might be able to provide an explanation.

 Not easy to relate the scenario at the times it happened inasmuch as it only started doing this on a long motorway run this last Saturday and as it all manifests so suddenly / quickly my attention is almost fully diverted to cancelling the auto braking and checking the situation behind.

However, I do recall one instance where I was in lane 2.

I guess it's falsely identifying something ahead of you as an obstruction in your lane. Were there overbridges at the junctions where it happened? I'd get it checked at the dealers but I bet they will want to charge you for re-calibration. 

Why would they not charge for recalibration? I can’t think of any company that wouldn’t. 

I had this issue and solved it by turning off a setting something like 'recognise the road you're on'.

You may find the slip road isn't the problem, rather that it allows access to a motorway that crosses underneath the one you're on.

My guess is that the car was using the sat-nav maps and seeing what it thought was a crossroads approaching so braked on the approach.

I haven't got access to my car now but I think I found it in the settings menu for the ACC rather than the sat-nav but I could be mistaken - it wouldn't be the first time 🙄