Accident due to TJA/ACC use.

[fnegroni]

This will be a long post to share some observations, not yet confirmed.
.

Have you got an OBD2 dongle? If not, are you local to London?
would be nice to check exactly what the car is doing a plot it on a graph. I’ll do what you tried there and take an energy consumption graph too. But I wonder if it charges from car to car.

 

[DixieTGS]

This will be a long post to share some observations, not yet confirmed.

While in my first months of ownership, i was obsessing over efficiency and i found out that if i do city driving with lots and lots of traffic stops, my consumption was way higher than without stop/go traffic. This is quite common and expected, but while i was perfecting the slowest starts ever (single digit %s) performed and i annoyed hundreds of drivers behind me... still my efficiency was not all back. I also perfected stopping to red lights by using regen only, not one pedal mode, and annoyed even more drivers. Still not good.

Then i noticed that while i was stopped, the car would use between 3-6% power, but not moving an inch. I dismissed it as a UI glitch for weeks. And then one day while parking i noticed that the slow creep uses about the same power, i was making a 20 point parking by that time.

So, my theory was that if i stop really slow by only regen braking and maybe a feather bit more brake to fully stop, the power would go to 0% and when i lift the foot of higher on the brake it goes to around 4% (sometimes more or less, but not much). The car is 99% of the time not moving at all (flat streets where i live), but my theory is that the car is indeed using some small power but not enough to move the car. Too early to say, but for over a week i try to fully press the brake pedal then release and at least i never see that 'vampire drain' and it feels like my city consumption is somewhat lower.

Weirdly, i never saw this mentioned in any of the hypermiling videos.

Would love to hear if this is noticed by more people?

And to the OP, it seems like the car was not on a 0.0% incline street and that small power output was not enough to hold the car in place, so gravity did its thing sadly.

Edit: i realized i don't fully lift the foot off the brake...

If you don't use auto hold or it is not engaged you can see that on the brake symbol. If the HHC has kicked in it will take some power which may increase to over 30% on steeper hills, and stay like that until you pull away or according to the manual 'for a short time' whatever that means.

Anyway, the solution is simple I think: If you see power actually being used while stationary turn on the parking brake, it turns off as you pull away.

Using auto hold correctly should render the above unnecessary.

Using HHC for an extended time would seem bad to me - potentially high current in the motor with little or no air flow over it?

 

[Anon70]

Tend to use the autohold whenever stopped for more than a few seconds as the power drops from around 4% to zero when handbrake is on. I know it's not much of a saving but can't see the point in using traction power "idling" in an electric car

 

[mg4]

I don't use auto hold, never got used to it, especially when I want to make tight manoeuvres, i.e. parallel park. To disengage the brake I have to press the accelerator and if I do it harder than needed I risk slamming into a car in front of me.

I will train myself to fully apply the brakes I guess, but I wanted to make sure the behaviour is not a one off. And it seemed fundamentally related to the OP?

 

[Ekips]

I don't use auto hold, never got used to it, especially when I want to make tight manoeuvres, i.e. parallel park. To disengage the brake I have to press the accelerator and if I do it harder than needed I risk slamming into a car in front of me.

I will train myself to fully apply the brakes I guess, but I wanted to make sure the behaviour is not a one off. And it seemed fundamentally related to the OP?

You can just fully press down the brake pedal again to disengage auto hold that way you get control for tight manoeuvres

 

[siteguru]

Agreed. And the car shouldn't suddenly lurch forward (or back) ... it'll creep as you lift off the brake.

 

[melvinolotus]

Hi, today i used TJA/ACC the car stopped after another vehicle as expected at red light. The problem is that after a few seconds the car starts to roll back and hit the car behind (the power meter showed 16% power)

Conditions:

• Almost flat road, not crazy uphill
• excellent weather.

The damage is almost nonexistent, but I am 99% sure that this behaviour of the car could have been easily prevented if the dealer would update all modules and not mix software versions as I asked them to do. Very annoying.

Why not put the handbrake on

 

[Starplots]

Were you using one pedal driving? Several owners have reported the car rolls backwards when they've stopped on a downward incline.

I don’t have 1-pedal driving (Exclusive/Luxury/Trophy MY22) with R46. I had exactly the same thing happen yesterday in TJA. I didn’t touch any pedals, auto hold was on but I didn’t brake. The car stopped on a slight incline when it got to the correct distance from the stopped behind front and after a few seconds started to roll back.
I’ll be calling my dealer on Tuesday!

 

[BingBong]

I don’t have 1-pedal driving (Exclusive/Luxury/Trophy MY22) with R46. I had exactly the same thing happen yesterday in TJA. I didn’t touch any pedals, auto hold was on but I didn’t brake. The car stopped on a slight incline when it got to the correct distance from the stopped behind front and after a few seconds started to roll back.
I’ll be calling my dealer on Tuesday!

Please keep us updated if you find any solution.

 

[NLMGSAN]

Please keep us updated if you find any solution.

So what causes it : acc or tja?

 

[BingBong]

So what causes it : acc or tja?

Probably ACC, i don't know why. I tried it again today and it worked well

 

[rabacon001]

Hill Hold works most of the time with ACC but just occasionally it doesn't and the car will roll back. It caught me out once as I thought I had stopped and went to press the A/C button when I suddenly perceived movement out of the corner of my eye and slammed my foot on the brake just in time not to roll back into the vehicle behind. It has made me a lot more cautious, as someone else mentioned, we should be in control of our vehicles at all times.

 

[Watts Efficient]

It didnt used to do this until the latest software update as well!!!! I am actually pretty hacked off about the lastest update to the LKA/TJA its made mine far worse and thats one thing I noticed straight away!!

agree with you. I recently updated the software and when I use TJA my car stirs right crossing the lane

 

[siteguru]

After the update last year my LKA was better ... TJA however was just as bad if not worse. (The two systems are subtly different).

 

[ReintjeWA]

I find with TJA the car gets a little obsessed with being in the middle of the lane, which isn’t always where one wants to be, for instance around cyclists, motorcycles splitting lanes, or if you see kids/pets waiting to cross, I tend to move away from them a little, but the car then starts pulling you back in. Or (Aussie specific ) overtaking a road train, I prefer to hang as far right in my lane as possible.

I thought that would be mostly a LKA thing, but it seems more intrusive when on TJA, perhaps that is just in my head of course.

 

[Lord Randall]

@siteguru my car automatically engage auto hold any time it stops. No need for pedal pushing.

A case of unwanted rollback happened to me too, but was uphill while crawling into traffic with TJA active at very low speed.
I immediatly reacted, so no damage, but still.. you lose a bit of confidence on the car.

 

[siteguru]

@siteguru my car automatically engage auto hold any time it stops. No need for pedal pushing.

It might be helpful if you quoted which of my posts you're replying to ... neither of the one's on this page seem to have much relevance to what you've typed as a response.

 

[Lord Randall]

It might be helpful if you quoted which of my posts you're replying to ... neither of the one's on this page seem to have much relevance to what you've typed as a response.

You were speaking about fully pushing brake pedal to engage auto hold. But not all the models works like this.

I'm late to the party, I was reading the whole trend.

 

[Lillemy]

My car has always rolled back if using ACC and traffic stops uphill.

Thought it is just how it is working, so every time I now put my foot on the brake.

Will mention for dealer at next service.

 

[NLMGSAN]

@siteguru my car automatically engage auto hold any time it stops. No need for pedal pushing.

A case of unwanted rollback happened to me too, but was uphill while crawling into traffic with TJA active at very low speed.
I immediatly reacted, so no damage, but still.. you lose a bit of confidence on the car.

Are you using OPD?