Adaptive cruise control (ACC) behaving badly? Check your number plate.

[ntompson]

Update as of 27 December 2021: if you're having issues with ACC, check how your front number plate is installed; it could be blocking the radar - see post #17 below.

Original post:

Hi all,

First post from a happy new MG ZS EV owner. I'd love to hear about your experience with adaptive cruise control (ACC) to know if what I am experiencing is abnormal and could be an indication of a fault.

Among the many cool features I'm learning, I've been quite impressed with the ACC. It's handled busy stop / start traffic scenarios quite well (not always super smooth, but pretty good nonetheless).

Having said that, I've had a few cases where ACC suddenly decides to slow the car down for no obvious reason (no traffic ahead of me or coming towards me). One example is along a straight (wide) suburban main road when passing a parked car. Another example is a straight suburban road with a large concrete embankment quite close to the edge of the road (this one has happened on multiple passes of the same spot). Both are 50 km/h zones.

In these cases, ACC suddenly throttles back and then half a second later applies the brakes (which makes a bad sound). I'm not completely confident, but it sounds / feels like the braking is heaviest on the left hand side of the car (we drive on the left in Australia).

One observation is that this has only happened when the sun angle is relatively low creating a little glare looking through the windscreen (but not that much). I had assumed that ACC only uses the radar, but maybe it also uses the windscreen camera? The windscreen is clean.

So I'd appreciate the benefit of your experience: is this is a common occurrence for ACC in the MG ZS EV? Or is this unusual and I should assume that something is wrong, needing fixing? It's a rather unsettling experience and makes me nervous about what might happen at higher speeds.

Many thanks,

Nick

Original title: Unexpected braking when using adaptive cruise control (ACC)

 

[Yu1234]

I use ACC in UK on motorway network on way to work in mornings, at 3am traffic is virtually non existent, so is perfect time to use it.

On slight bends, i.e when exiting, entering slip roads, the vehicle does slow down and speed up inconsistently, with the rev counter jumping up and down, seems like the sensitivity is high

 

[Kithmo]

This may not be the ACC it may be the AEB detecting the possibility of a collision if you approach a hazard too fast or steer around it too late. Try the same route without ACC on and if I'm right it will still do the same.

 

[Kithmo]

I use ACC in UK on motorway network on way to work in mornings, at 3am traffic is virtually non existent, so is perfect time to use it.

On slight bends, i.e when exiting, entering slip roads, the vehicle does slow down and speed up inconsistently, with the rev counter jumping up and down, seems like the sensitivity is high

rev counter ?

 

[Tim Green]

I have the same problem on one particular road. I think it is a very slight curve that the radar sees. It is rather annoying but I now know not to use it on that road.

 

[rbpasapera]

I always turn the collision alert sensitivity down to 'Low' on every drive so it won't have too many false alarms.

 

[Kithmo]

I always turn the collision alert sensitivity down to 'Low' on every drive so it won't have too many false alarms.

The forward collision system stays on whatever setting you had it previously, not sure about the AEB for pedestrians.

 

[rbpasapera]

The forward collision system stays on whatever setting you had it previously, not sure about the AEB for pedestrians.

This FCS sensitivity setting keeps defaulting to Normal, so I need to change it to Low on every drive.

 

[Kithmo]

This FCS sensitivity setting keeps defaulting to Normal, so I need to change it to Low on every drive.

According to the manual it should stay as it was, but having said that, I leave mine on normal anyway so either way it's the same as it was.

 

[ntompson]

Hi - thank you all for your replies and apologies for the late response - I think maybe subscription notifications were going to my spam.

I had also started to wonder whether it was actually the forward collision system that was causing the problems and not ACC. I'm still not quite sure, to be honest. I have rerun the same route without ACC and not had sudden braking occur, but I've also had it both ways with ACC active - so it is hard to be definitive.

More recently, I've tried deactivating the FCS system. Since doing that, I've had one occasion where FCS shouted at me (big red noisy alert) - it was triggered by a car ahead of me drifting slightly from their lane towards mine. No real danger. I can only guess whether the car would have braked in that case had FCS been active. In this case, ACC was not active.

I need to do some more test runs to get a better idea, but perhaps the question I should be asking is: do people generally find that these systems (ACC / FCS / AEB / lane keeping) commonly suffer from false positives (that is, they go off when there was no real danger)?

In other words: is this stuff all a bit crap and I might as well turn it off, or are the overreactions of my car possibly indicating a fault?

Thanks,

Nick

 

[mj224]

I get the same response on a particular corner locally, especially if there is a parked car there. The MG ACC is detecting a possible hazard I guess, and acting accordingly.

I do use the ACC quite a lot on local roads, especially on the straights. But as said, its really designed for motorway/dual carriageway type roads...

 

[Archev]

I’ve had that happen with my previous ZS and current 5LR too. I’ve always just put it down to the hypersensitive timidness of the wee guy down there in the gubbins who actually presses the brake pedal and pulls the warning chain ?. Steer away from such situations and his lane keeper mate screams at you and wobbles the steering wheel.
Evict them or switch them off !

 

[Gomev]

Remember it's just a computer working to set parameters with set actions.
It is not intuitive and does not know for example that the car in front has slowed because it is turning left. You know it will be gone by the time you get there, it doesn't. It just sees a vehicle that it interprets as virtually stationary, i.e. not going forwards in the same direction as you, in effect it is reacting to you closing in rapidly on a static vehicle.

 

[Kithmo]

I just got used to it on the Prius and the ZS and altered my driving style to suit.
Leave more distance to the vehicles ahead and approach other hazards like parked cars slower or at least with you foot off the accelerator.
The only time I've had a false reaction from it was in low, bright sunlight as I was approaching a bridge, it interpreted the shadow of the bridge as something else.

 

[ntompson]

OK - thanks all. Sounds like what I am experiencing is situation normal. It would be nice if it were possible to turn some of these features off, but I've noticed that they all come on again after turning the car off and back on again. A little annoying.

As suggested, I'll not expect so much from ACC in built up areas. It's a bit of step backwards, though. My previous car (a 2014 VW Polo) had the less fancy kind of non-adaptive cruise control. I'm sure it saved me many a speeding fine on boring suburban 50 km/h streets, where it's all too easy to sneak up the speed without realising. Oh well.

 

[Gomev]

OK - thanks all. Sounds like what I am experiencing is situation normal. It would be nice if it were possible to turn some of these features off, but I've noticed that they all come on again after turning the car off and back on again. A little annoying.

As suggested, I'll not expect so much from ACC in built up areas. It's a bit of step backwards, though. My previous car (a 2014 VW Polo) had the less fancy kind of non-adaptive cruise control. I'm sure it saved me many a speeding fine on boring suburban 50 km/h streets, where it's all too easy to sneak up the speed without realising. Oh well.

I used ACC a great deal in urban areas, particularly in heavy traffic. Set at 30mph/50km/h and let it do the work.

 

[ntompson]

TL;DR: if you're having issues with ACC, check how your front number plate is installed; it could be blocking the radar.

Hi again - an update. Contrary to many of the responses to my OP, our ACC experience continued to be poor. Sudden braking would occur in otherwise ideal conditions - straight road, parked cars and so on. I think I've figured it out... Take a look at how our number plate was installed straight from the dealer:

If you're not familiar with where it is, that small black rectangle below (and behind) the number plate is the radar. I would guess around half of the radar's vertical field of view is blocked by a metal object (the number plate). It's a miracle it worked at all.

My guess is that the radar beams that see further down the road were blocked by the number plate, meaning that objects only become visible to the radar when they are relatively close. So the ACC reacts dramatically because it figures something suddenly leapt in front of the car.

A couple of extra holes in the number plate later to shift it upwards, and the ACC is behaving much more politely.

So if anyone else has been suspicious about the performance of their ACC, I'd highly recommend checking the number plate. This will be particularly relevant for Australian drivers: our number plates are somewhat taller than European plates.

I'm a little surprised that the dealer didn't think about this...

Hope my experience helps someone!

 

[ChrisR]

TL;DR: if you're having issues with ACC, check how your front number plate is installed; it could be blocking the radar.

Hi again - an update. Contrary to many of the responses to my OP, our ACC experience continued to be poor. Sudden braking would occur in otherwise ideal conditions - straight road, parked cars and so on. I think I've figured it out... Take a look at how our number plate was installed straight from the dealer:

View attachment 6075

If you're not familiar with where it is, that small black rectangle below (and behind) the number plate is the radar. I would guess around half of the radar's vertical field of view is blocked by a metal object (the number plate). It's a miracle it worked at all.

My guess is that the radar beams that see further down the road were blocked by the number plate, meaning that objects only become visible to the radar when they are relatively close. So the ACC reacts dramatically because it figures something suddenly leapt in front of the car.

A couple of extra holes in the number plate later to shift it upwards, and the ACC is behaving much more politely.

View attachment 6076

So if anyone else has been suspicious about the performance of their ACC, I'd highly recommend checking the number plate. This will be particularly relevant for Australian drivers: our number plates are somewhat taller than European plates.

I'm a little surprised that the dealer didn't think about this...

Hope my experience helps someone!

Good detective work there @ntompson, I'd say you're right. Mine has a slimline number plate on the front (as fitted by the dealers to the demo model) that avoids this situation and maybe they were aware of the problem.

I only use ACC over 100km/h on the highway and it's always been fine. My only issue is that when the car slows down for a slower car in front when I change lanes to pass it takes a while to come back up to speed so passing isn't quick.

 

[Deleted member 7171]

TL;DR: if you're having issues with ACC, check how your front number plate is installed; it could be blocking the radar.

Hi again - an update. Contrary to many of the responses to my OP, our ACC experience continued to be poor. Sudden braking would occur in otherwise ideal conditions - straight road, parked cars and so on. I think I've figured it out... Take a look at how our number plate was installed straight from the dealer:

View attachment 6075

If you're not familiar with where it is, that small black rectangle below (and behind) the number plate is the radar. I would guess around half of the radar's vertical field of view is blocked by a metal object (the number plate). It's a miracle it worked at all.

My guess is that the radar beams that see further down the road were blocked by the number plate, meaning that objects only become visible to the radar when they are relatively close. So the ACC reacts dramatically because it figures something suddenly leapt in front of the car.

A couple of extra holes in the number plate later to shift it upwards, and the ACC is behaving much more politely.

View attachment 6076

So if anyone else has been suspicious about the performance of their ACC, I'd highly recommend checking the number plate. This will be particularly relevant for Australian drivers: our number plates are somewhat taller than European plates.

I'm a little surprised that the dealer didn't think about this...

Hope my experience helps someone!

I'd have a word with your dealer. They should know better!