Phantom Braking when in Alert Only Mode

[TedB]

I always turn off LKA and now Front Collision Assist before starting every journey since nearly being rear ended after starting to overtake a parked car a few months ago when my MG4 Trophy suddenly jammed the brakes on. However, yesterday while driving through a built up area at about 35mph in a 40 limit with no other vehicles in front or behind the car suddenly jammed the brakes on and off again for no apparent reason whatsoever. Importantly the software was set to alert only as seen in the screen shot. Anyone else experienced this or have any idea why it might have happened?

 

[Martinonline]

Were you using ACC or TJA?

 

[TedB]

Were you using ACC or TJA?

No they were both off.

 

[Rolfe]

I find that when using ACC the car will see a parked car and clock it as being in front of me in my lane, so slow down. It's bloody annoying, but I can see what's happening. It doesn't happen unless ACC is on, and it doesn't slam on the brakes.

 

[fnegroni]

Possibly a bug.
Although AEB would have prevented the idiot who rear ended me the other week from messing up my car.

 

[Roberto 2761]

I always turn off LKA and now Front Collision Assist before starting every journey since nearly being rear ended after starting to overtake a parked car a few months ago when my MG4 Trophy suddenly jammed the brakes on. However, yesterday while driving through a built up area at about 35mph in a 40 limit with no other vehicles in front or behind the car suddenly jammed the brakes on and off again for no apparent reason whatsoever. Importantly the software was set to alert only as seen in the screen shot. Anyone else experienced this or have any idea why it might have happened?

Yes had the same thing with my trophy when passing parked cars and about to turn right
Quite crazy.

 

[Wil Tryharder]

I’ve been running an experiment for the last couple of weeks. Always turn LKA to alert only, also Front Collision Assist to alert only, then drive as best I can in between the lines. It almost works ok, most of the time. But when I attempt to drive with ACC the trouble starts. Mostly it’s just straight up phantom braking seeing on coming cars in front. But sometimes large amounts of road markings and narrower roads bring on random slowdowns even with no traffic. So…. Just have to go without I guess ?

 

[fnegroni]

I’ve been running an experiment for the last couple of weeks. Always turn LKA to alert only, also Front Collision Assist to alert only, then drive as best I can in between the lines. It almost works ok, most of the time. But when I attempt to drive with ACC the trouble starts. Mostly it’s just straight up phantom braking seeing on coming cars in front. But sometimes large amounts of road markings and narrower roads bring on random slowdowns even with no traffic. So…. Just have to go without I guess ?

Are you using ACC on like urban roads and b roads and such?

 

[Wil Tryharder]

I’m just on the edge of urban and country. Most of the urban roads are really very wide, usually with a parking or cycle lane, that’s mostly as wide as a car. The country roads or ‘connection’ roads between towns are also really wide, and basically well marked. They have very (some would say) generous speed limits 80 - 100 kph. A parked car in a feed in lane (driver stopped to use phone) or parked on the ‘nature strip’ (verge) will almost certainly slow the car down.

My town is famous in Aus for having 21 roundabouts and only 3 sets of traffic lights. Clearly the road system here was designed by someone from Basingstoke ?. Most days the traffic really flows. One pedal driving here is a blast. I mainly use ACC for limiting speed.

I think I read in the manual that LKA isn’t active below 60kph so around town it’s not a problem. The ACC on the hand will phantom brake below 60kph even if LKA and Front Collision Assist are set to alert only.

I’ve just had a bunch of updates done at my local dealer and there’s no change.

 

[NLMGSAN]

A parked car in a feed in lane (driver stopped to use phone) or parked on the ‘nature strip’ (verge) will almost certainly slow the car down.

Does the system trigger the brakes with cars on both sides, or only on one side?
Reason I'm saying this: I had similar issues with cars to the right. These cars were taking right turns, me going straight ahead. It caused slamming the brakes. They updated/calibrated camera and radar. Now it happens only occasionally because the system falsely interprets a car is in front of me in the same lane (e.g. in bends or crossings). But it usually corrects itself quickly.

Btw, I would never use ACC in rural areas. It is not made for that. Particularly these roundabouts can be dangerous places with acc at 50kph and 'nobody' ahead of you.... That's when I would use the speed limiter. But only occasionally because speed limits vary too often in towns (30,40,50,60,80 kmh).

 

[Martinonline]

The ACC is working as intended, that is to keep you a fixed distance from the car in front of you by braking or accelerating. Unfortunately the sensor systems are not good enough for use in town conditions where parked cars and cars edging towards your lane confuse them.

 

[Wil Tryharder]

Does the system trigger the brakes with cars on both sides, or only on one side?

Yes it does.
Oncoming traffic turning right is a problem. I slowly getting used to the idea of never using ACC again. But it’s taking a while, I used the bog standard cruise control (no sensors) in my old ice Peugeot a lot.
I’d swap the dedicated HVAC + ~ buttons for a on off LKA, or two more programmable buttons so that WE can decide.

 

[Wil Tryharder]

Unfortunately the sensor systems are not good enough

That’s it in a nutshell ?

 

[NLMGSAN]

Yes it does.
Oncoming traffic turning right is a problem. I slowly getting used to the idea of never using ACC again. But it’s taking a while, I used the bog standard cruise control (no sensors) in my old ice Peugeot a lot.
I’d swap the dedicated HVAC + ~ buttons for a on off LKA, or two more programmable buttons so that WE can decide.

I would definitely ask for a recalibration, in particular the radar.
Another thing: did you have your wheels aligned?

 

[Wil Tryharder]

Another thing: did you have your wheels aligned?

OK, I may have made an amateur assumption here. With the car being bought brand new from a dealer. I assumed the wheel alignment would be spot on. For a while anyway. I haven’t hit any kerbs yet, even with LKA trying its best.
I do get free checks from the place I used to take my bone shaker, so I’ll pay them a visit.
Which brings up another question. Is the consensus that EVs being heavier will mis-align quicker? The buzz locally is that with 21 roundabouts in the town the front near side wheel takes more abuse than normal.

 

[NLMGSAN]

I asked because if so, radar and camera need tuning (it's in the manual).

Your car is heavier than a normal petrol car. But it would surprise me if this would result in misalignment. If there is no wobble and the car does not pull sideways, I would not worry.

 

[Ian Key]

Which brings up another question. Is the consensus that EVs being heavier will mis-align quicker? The buzz locally is that with 21 roundabouts in the town the front near side wheel takes more abuse than normal.

A lot of SUV's are heavier than the MG4 and they don't have misalignment problems.

 

[NLMGSAN]

How about SUV plugins...? They are heavy because of the petrol engine, EV motor and the ever increasing battery size to compete with full BEV's.