MGS5 safety software fault - recall level problem?

[Delascas]

I today “discovered” a potential very serious safety bug with our 2 week old MGS5 - the joys of being an early adopter.

Steps to recreate this problem:

1. Drive in OPD mode - get up some speed
2. Do a hard stop/panic stop with the brake pedal
3. Come to a full stop then quickly take your foot off the brake - one would expect the auto-hold feature to hold the car in place
4. Instead the car starts to roll backwards. Actually it was more than roll . .it feels like the car is under power moving backwards as the harder the stop seemed to influence how fast it drove in reverse. The D indicator stays on the entire time - in my final test, done on a flat road, I let the car drive in reverse for 10 meters before stopping it.
5. Pressing the brake a second time does stop this reverse motion.

I will pop into to my dealer this weekend . . but I would ask that another MGS5 owner tests this bug - clearly on an empty road! In bumper to bumper traffic, this could easily cause an accident.

 

[Alb]

That does sound odd but from a practical perspective, if I'd just done a panic stop, removing my foot from the brake wouldn't be top on my list of priorities. Did your research extend to measuring the maximum period of time you could stay on the brake with this still happening? Are we talking milliseconds or seconds?

 

[Delascas]

That does sound odd but from a practical perspective, if I'd just done a panic stop, removing my foot from the brake wouldn't be top on my list of priorities. Did your research extend to measuring the maximum period of time you could stay on the brake with this still happening? Are we talking milliseconds or seconds?

I'm not sure I agree about "removing my foot . . .wouldn't be on my list of priorities" . . . I come to the MSS5 from prior EV's with OPD . . and once you really get used to it everyday, not having your foot on the brake is the "natural" state - so I let up on it without conscious thought.

The timing question is a good one . . . I was going to try to rig up my mobile phone to video this behavior. I will play around tomorrow and try to figure that out.

 

[Ian Key]

There is a thread on the MG4 forum about the MG4 rolling backwards when using OPD

Thread 'OPD, car rolls backwards when stopping on downhill slopes (merged thread)'

Feb 23, 2024

Hello,
I am making a quick call to get your feedback on my use case.



Every morning, I leave home (1) and activate the one-pedal (UC with OP only). On the downhill road (not depending charge level), my MG4 regenerates strongly in this phase with peaks to -25.
The deceleration is not sufficient to stop before the panel, on the false flat going down I apply a little brake. (2)

I hear rubbing noises from the brakes, my car stops, I release the brake and then the...

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[yycools]

I'm not sure I agree about "removing my foot . . .wouldn't be on my list of priorities" . . . I come to the MSS5 from prior EV's with OPD . . and once you really get used to it everyday, not having your foot on the brake is the "natural" state - so I let up on it without conscious thought.

The timing question is a good one . . . I was going to try to rig up my mobile phone to video this behavior. I will play around tomorrow and try to figure that out.

Yes, we've experienced this just the other day, using OPD and had to apply hard braking due to the sudden stopping of the car in front. Released the brake once the car had stopped because I thought brake hold would take over, but instead the car started to roll backwards for a few meters. We were able to recreate this even at slower speeds. all you have to do is on OPD, apply hard braking and release the brake within 1 sec of stopping, and it'll roll backwards (rollback distance depends on how fast you stopped from/how hard you braked). We will bring this up with our dealer here, and the issue is not wether you "should" release your brake upon stopping, it is about why the car roll backwards once braking is no longer applied....

 

[Delascas]

So I had some time this morning and found a deserted single track road . . . I can recreate this behavior at will. I am not convinced this is the same problem as was reported in the MG4 - because the car is 100% going backwards under power - its not "just" rolling. I suspect what's happening is a hard stop generates significant regenerative energy and the car is mistakenly converting some of that into kinetic energy. The faster I drove, the harder the panic stop . . . the backwards motion was then faster and lasted longer. If I didn't press the brake again, the backwards motion would "fade away" after about 3 seconds and then comes to a full stop . . . but in that time the car can travel 6-10 meters/yards. Thanks @yycools for confirming this is not just a problem in mine.

 

[Delascas]

After @yycools confirmation, I reported this both MG (https://www.mg.co.uk/contact-us) and filed a report with the UK DOT here: Vehicle recalls and faults

I would ask any MGS5 owner in the UK to report this to the UK Gov. This WILL cause a minor RTA - probably on the M25 and almost certainly by backing into the Audi who is always right on my arse . . or is that just me???

 

[yycools]

I checked with my MG sales team today, and they replied quite quickly:

I have just checked with the technical manager. He mentioned this is the characteristic of one pedal drive. When your car stop, you need to step on the brake and the autohold function will be activated to hold the car then you can lift off your foot. This is to protect the motor system. You can check with Tesla one pedal and it’s the same characteristic too.

I am less concerned about it tbh, I did do a search on telsa forums and it seems like a thing, basically if using OPD, just step on the brake long enough to activate auto hold.

 

[yycools]

This is what it looks like:


car will roll backward if on OPD, using brake to stop, but lift brake before auto hold engages....

 

[Delascas]

Thanks for the video @yycools . But I think the dealer you spoke with is full of it - one of my prior EV's was a gen2 Leaf with it's ePedal OPD system . . it most certainly did NOT do this. The only video I can find about Tesla's exhibiting this behavior is here (This Tesla seems to roll backward - no hold?) . . . but as you can see, the situation is totally different - he was fully stopped for 5-6 seconds before he started to roll back. The discussion in the thread explains what three settings in a Tesla might generate that effect.

What I think your dealer might have been referring to is the problem of EV's being at 100% full charge . .then regen breaking and therefore OPD does not work. That's a problem that all EV's do have . . as at 100% charge there is just no place to store any generated power. Both my prior Leaf and ID.4 had that issue and I've not tested it . . but I'll bet the MGS5 also does.

I do not see how a car set to DRIVE can go into reverse (under some level of power) and this be anything but a software bug. In fact . . .how would this behavior interact with the Rear Cross Traffic Alert ( RCTA ) and Rear Cross Traffic Brake (RCTB) features? I'm not brave enough to go out and try, would would the RCTB system stop the MGS5 from actually hitting a trailing car??

I've already opened a case with the UK DVLA . . so we shall see . . . Thanks agin your video!

 

[yycools]

Feel free to use my video, in fact, here are my observations, which were demonstrated in the video (state of charge ~45%)

1. Car rolls backward under some power rolling backwards with OPD and stopped with brake, lifting brake within 1-2 secs of stopping
2. Roll back will fade within 2-3secs
3. Car will start to creep forward once backward roll stops
4. OPD does not seem to work under this condition
5. Once pressed on Brake long enough for brake hold to engage, everything will work as normal again

 

[decrep]

I have a bit of a theory. (and it's only a BIT of a theory)
Engaging regen is effectively putting the car in reverse, so the motor charges the battery.
When the friction brake lets go the motor is still driving backwards.
If the car has stopped, foot of brake should disengage regen at the same time and apply auto hold.

I could be way off here, but looks like a software bug to me.

 

[EvTek23]

@yycools I don't seem to be able to see your video on my phone using the browser on the MGEVs site. Just see error 403

 

[yycools]

Direct link if you can't view the embedded video:
Link