Sudden acceleration

Edd Beesley · Aug 28, 2024

mozza said:
This same thing happens to me, any bump whilst braking will cause the car to fly forward. Sick of reading all this bollocks about driver error. Car is just faulty, I still drive it, I'm used to it and expect it to happen.

It's a common thing with cars with regen - they are very sensitive to traction loss and turn off the regen immediately. This sudden reduction in braking force -feels- like you are suddenly accelerating but you're not. The mechanical brakes are still there and still work and if there was a need for you to increase braking force you can just push the pedal harder

fnegroni · Aug 28, 2024

After 5k miles on the original tyres and 6k miles on their replacement, I blame most (if not all) problems people are having wrt handling, traction and regen to the rubbish OE tyres (whether conti or Bridgestone) and their China-only compound

Kimiko · Feb 1, 2025

les said:
Has anyone experienced the car accelerating fast without warning?
I’ve just tried to park, took my foot off the accelerator and the car shot forward. Just checked and it has hit the parking bollard, denting the front bumper a little.
Did the ACC kick in?
Felt it did this earlier too.
Another scary experience. I’m shaking.

Hey, did you got an explanation of this? I’ve just experienced the exactly same thing, and not sure what to do now.

neeti · Sunday at 7:20 AM

les said:
Has anyone experienced the car accelerating fast without warning?
I’ve just tried to park, took my foot off the accelerator and the car shot forward. Just checked and it has hit the parking bollard, denting the front bumper a little.
Did the ACC kick in?
Felt it did this earlier too.
Another scary experience. I’m shaking.

Dear Les
Something similar happened to me yesterday in MG4 Trophy. Would you be able to tell me what the outcome was for you?
Much appreciated.
Neeti

Kimiko said:
Hey, did you got an explanation of this? I’ve just experienced the exactly same thing, and not sure what to do now.

Me too Kimiko. It happened yesterday to me. What did you do?

Tuareg · Sunday at 8:09 AM

Wow 2 first posts again. lol.

fnegroni · Sunday at 10:36 AM

May I suggest @Kimiko and @neeti - take a picture of the accelerator pedal and the area surrounding it. It might be something stuck like the carpet or something.

neeti · Sunday at 9:33 PM

Chequers said:
Another one accelerating out of control posted on the MG4 Drivers UK Facebook group.

driving away from a roundabout the car suddenly accelerated and despite the driver standing on the brake pedal the wheels were spinning at top speed, car did a 360 then ended up on the grass verge.

MG need to get on top of this before the motoring press pick up on it.

Do you know where I can find out more about this? Something similar happened to me.

pollenface · Sunday at 10:25 PM

Kithmo said:
Check the floormat hasn't come off it's hold down clips and slipped forward. One of my clips had come undone.

Once the floor mat stopped me from getting full throttle, I thought there was something seriously wrong with the car until I realised that

crispyjay · Monday at 12:18 PM

bowfer said:
That’s not acceleration, that’s just the braking being interrupted by a tyre slipping.
It’s not acceleration as such.

If you’re braking going downhill when the brakes stop working - you accelerate! My MG5 does this and it’s quite scary.

DannySB1 · Monday at 12:53 PM

Edd Beesley said:
It's a common thing with cars with regen - they are very sensitive to traction loss and turn off the regen immediately. This sudden reduction in braking force -feels- like you are suddenly accelerating but you're not. The mechanical brakes are still there and still work and if there was a need for you to increase braking force you can just push the pedal harder

This is actually one of the few things that has taken some getting used to for me.
Slowing down with the help of regen only for it to suddenly back off and rely entirely on the friction brakes. It definitely can catch you by surprise if you're not paying attention!

fnegroni · Monday at 4:38 PM

Why would regen suddenly stop? I’ve never had that happen to me in 18 months of ownership

Graydo · Monday at 4:57 PM

My Zs hybrid plus suddenly accelerated coming out of a car park a few days ago, I braked and all was fine, but I worked out that the culprit was me pressing the cruise control button instead of the regen button on the left side of the steering wheel.

They are small buttons and right next to each other so as my cruise control was set at 60 mph it took off and tried to reach that speed.

One to watch out for.

Graydo

nanomad · Monday at 4:57 PM

@fnegroni Regen braking is the first thing the stability control module kills as soon as it feels one of the rear wheels slip compared to the other.

I can trigger it quite reliably by having one wheel on a wet and freshly painted crosswalk line and the other on the asphalt while the car is slowing down

fnegroni · Monday at 5:01 PM

nanomad said:
@fnegroni Regen braking is the first thing the stability control module kills as soon as it feels one of the rear wheels slip compared to the other.

I can trigger it quite reliably by having one wheel on a wet and freshly painted crosswalk line and the other on the asphalt while the car is slowing down

Now I see. Yeah that had happened to me with the stock tyres. Never happened again since I put the new tyres on.
But I personally didn’t think of it as a sudden regen stop; to my mind sudden regen stop means ‘out of the blue for no apparent reason’ as opposed to ‘because the wheels lost traction’.
But I get it now.

nanomad · Monday at 5:07 PM

fnegroni said:
But I personally didn’t think of it as a sudden regen stop; to my mind sudden regen stop means ‘out of the blue for no apparent reason’ as opposed to ‘because the wheels lost traction’.

I can get you a "sudden deceleration" as well if you want, whoever did the integration testing on the different modules forgot to catch at least one other edge case:

Set the car to regen 1 (max 5% regen power)
Activate ACC / LKA
Foot off the accelerator
Wait for ACC/LKA to start a deceleration with a strength > 5%
Disable ACC/LKA (steering wheel button) without pressing the accellerator

Observe as the car keeps slowing down with regen > 5% despite being set to max 5% with no brake or accelerator input

Fortunately it looks like the inverse doesn't happen during acceleration, if you disable ACC while the car is accelerating without pressing the accelerator pedal it should revert to the correct amount of regen braking.

LenEV2016 · Monday at 6:57 PM

Tuareg said:
Wow 2 first posts again. lol.

What a surprise

Sudden acceleration

Edd Beesley

Established Member

fnegroni

Prominent Member

Kimiko

Novice Member

neeti

Novice Member

Tuareg

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fnegroni

Prominent Member

neeti

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pollenface

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crispyjay

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DannySB1

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fnegroni

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Graydo

Standard Member

nanomad

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fnegroni

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nanomad

Established Member

LenEV2016

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