Accident due to TJA/ACC use.

[BingBong]

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.

 

[siteguru]

You have my sympathies, but ultimately it's your fault, sorry ... you're supposed to be in control of your vehicle.

 

[BingBong]

You have my sympathies, but ultimately it's your fault, sorry ... you're supposed to be in control of your vehicle.

You 100% right, BUT i searched about this behavior here is the forum and looks like its known problem with ACC that guess what? Probably solved at the recent ACC/TJA software. Exactly like LKA, BT problems ans etc.

And still after all some dealers refuse to update the vehicle or lie that there is no update. All this can be solved by recall. Here in israel for example Chery did this on the Omoda 5 EV.

If MG wants customers to buy another MG after some while they should fix this problem (and in this case moat of the fixes is already exists). A lot of Chinese manufacturers is coming to Europe and if they want to stay relevant they should wakeup.

 

[Bricktop X PWR]

Did you not have Autohold activated or had you simply not pressed the brake pedal hard enough?

 

[siteguru]

The theory is that you can just sit there on ACC/TJA and it should hold the car until the one in front moves forward. If you engage auto-hold then it disengages ACC/TJA.

 

[BingBong]

Did you not have Autohold activated or had you simply not pressed the brake pedal hard enough?

I used acc and traffic jam assist, it should use the brakes on standstill behind other car. It most of the time do. Never had problem with auto-hold. I use auto hold all the time.

 

[Ian Key]

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

 

[Bricktop X PWR]

The theory is that you can just sit there on ACC/TJA and it should hold the car until the one in front moves forward. If you engage auto-hold then it disengages ACC/TJA.

Then it sounds a bit untrustworthy!

Ive never used TJA for what it was actually designed for, (crawling along in traffic) but regardless, the driver is ultimately in control and should have stopped the car rolling back.

Not bashing BingBong, BingBong, and I imagine you won't be trusting it again!

And....you're not alone, I've got my own gripes and am waiting for MG to get a grip of a known problem with my car.

I've also said that if they want MG customers of today to become repeat MG customers of tomorrow, then they had better start getting a grip of the issues some of us are dealing with.

 

[JonnyG]

The theory is that you can just sit there on ACC/TJA and it should hold the car until the one in front moves forward. ...........

So far that has how my car has behaved ............ but I will watch out on steeper inclines now !!

Not related but the other thing to watch out for is when in reverse gear Autohold does'nt work by just pressing hard on the brake.

Also on OPD the manual says :

"Note: Even if the One-Pedal function can achieve the parking effect, there will still be the risk of sliding in the case of large slope. Don't risk driving with the convenience of the One-Pedal function. Please always ensure effective parking."

 

[Tuareg]

You 100% right, BUT i searched about this behavior here is the forum and looks like its known problem with ACC that guess what? Probably solved at the recent ACC/TJA software. Exactly like LKA, BT problems ans etc.

And still after all some dealers refuse to update the vehicle or lie that there is no update. All this can be solved by recall. Here in israel for example Chery did this on the Omoda 5 EV.

If MG wants customers to buy another MG after some while they should fix this problem (and in this case moat of the fixes is already exists). A lot of Chinese manufacturers is coming to Europe and if they want to stay relevant they should wakeup.

You mention Israel but in your profile you have location set to EU. The cars in Israel are probably supplied/allocated under the Middle East region, so software etc might be different.

 

[wjohnson12321]

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!!

 

[DixieTGS]

So far that has how my car has behaved ............ but I will watch out on steeper inclines now !!

Not related but the other thing to watch out for is when in reverse gear Autohold does'nt work by just pressing hard on the brake.

Also on OPD the manual says :

"Note: Even if the One-Pedal function can achieve the parking effect, there will still be the risk of sliding in the case of large slope. Don't risk driving with the convenience of the One-Pedal function. Please always ensure effective parking."

There are some other odd display behaviours to to with OPD and other setting combinations. Normally when stopping on a steepish uphill when either brake is applied the power drops to 0. But I have seen it continue to consume 30% power even when pressing the foot brake enough to hold it, but weirdly the power reduces if you press really hard and comes back up again as the pressure is reduced. It's not a problem, just weird.

 

[siteguru]

Press hard and release = auto-hold engaged. (Parking light in the driver display turns green). Brakes are applied so power is removed from the motor.

Yes, I know the you pressing the brake pedal = brakes applied, but the car treats that differently for some reason, so appears* to keep some power applied to the motor.

* I'm not sure any power is actually applied.

 

[DixieTGS]

Agreed. I'm used to the display showing the last value before OPD stopped on the flat e.g. -7%, which stays until I move off.

However I'm intrigued as to how the brake pedal pressure alone can change the power display up and down, even though we suspect no power is actually applied.

I'll have to try and reproduce it one day and write the settings etc down.

 

[siteguru]

Brake pedal pressure followed by release = auto-hold. When the car detects that then it sets the motor power to 0%. If the car creeps after release then auto-hold hasn't activated.

 

[DixieTGS]

Ah, I suspect my odd behaviour is for the odd combination of OPD and auto hold off, Thanks. (I wasn't able to test as away from home till the weekend).

 

[DixieTGS]

Oh dear, I'd forgotten about HHC. It's probably working as designed and probably is using power as displayed. Hey ho.

 

[siteguru]

HHC?

 

[DixieTGS]

Hill hold control. I guess it was developed before they added auto hold? P196 in manual.

I've not driven ice automatics but suspect some of those have it.

 

[mg4]

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...