MG4 unresponsive

wdryan2023 · Jan 20, 2025

Twice in the last few days, my MG4 seems to have "shut down" for no apparent reason.

This appears to have happened, on both occasions, when I didn't lock the car with the key fob when leaving the car.

The wing mirrors remain out, but it's completely 'dead' and can't even get in. No response at all and the app is not responding either.

The last time, it 'rectified' itself by the the next morning although I had to leave it in the local village overnght.

It's after happening again this evening in the driveway at home.

Any ideas what's happening here and now to resolve.

Thanks in advance.

Jamesrr · Jan 20, 2025

wdryan2023 said:
...
Any ideas what's happening here and now to resolve.

Lock the car when you get out

Tsportcar · Jan 20, 2025

Is it possible you have a flat aux battery?

wdryan2023 · Jan 20, 2025

Jamesrr said:
Lock the car when you get out

Indeed, I know, I keep bloody forgetting.

Tsportcar said:
Is it possible you have a flat aux battery?

I guess it's possible. Odd though it 'resolved' itself last time.

Jamesrr · Jan 20, 2025

wdryan2023 said:
Indeed, I know, I keep bloody forgetting.

So does my better half. It's why I'm used to suggesting it

David9448 · Jan 20, 2025

Loose 12V battery terminal connection??

Tsportcar · Jan 20, 2025

wdryan2023 said:
I guess it's possible. Odd though it 'resolved' itself last time.

One way to prove it it to open the bonnet and put some jump leads on the battery to another car

Ian Key · Jan 21, 2025

Check the 12V battery terminals are tight.

You might need a software update as I thought the main traction battery should have kept the 12V battery topped up.

Tsportcar · Jan 21, 2025

Ian Key said:
Check the 12v battery terminals are tight.

You might need a software update as I thought the main traction battery should have kept the 12v battery topped up.

The 12V battery only gets topped up while the HV battery is active (When you are driving) or you are plugged in charging.

Ian Key · Jan 21, 2025

Tsportcar said:
The 12v battery only gets topped up while the HV battery is active (When you are driving) or you are plugged in charging.

Mine must be defective then as it also charges when it's switched off. When it's been sat on the drive locked for two days, not charging or connected to the charger, the battery voltage in the app has gone from 11.9V to 14.2V.

Tsportcar · Jan 21, 2025

Ian Key said:
Mine must be defective then as it also charges when it's switched off. When it's been sat on the drive locked for two days, not charging or connected to the charger, the battery voltage in the app has gone form 11.9v to 14.2v

To the left is were the car is charging while its being driven. To the right is were its charging when the battery is charging.

Geekice · Jan 21, 2025

Tsportcar said:
The 12v battery only gets topped up while the HV battery is active (When you are driving) or you are plugged in charging.

Same for me. I have a dashcam with two channels and a 4G module that is always on. A few times, I left the car for a week and noticed via the app that the HV battery occasionally recharges the 12V battery

Martinonline · Jan 21, 2025

As per the manual:

I believe the 12V battery will not be charged if DC charging.

Coulomb · Jan 21, 2025

Martinonline said:
I believe the 12V battery will not be charged if DC charging.

I think it's saying that the "automatic" charging is suspended when externally charging. While DC charging, the main contactors have to be on, so unless they go to a lot of trouble, the DC-DC will be active, charging the 12 V battery and powering all the pumps, fans, computers, etc.

The quoted manual section above doesn't differentiate between AC and DC charging, and we know that the 12 V battery gets charged when AC charging.

Martinonline · Jan 21, 2025

From the 'Fast Charging and Low Battery Warning' thread:

Evgen K said:
So, i did experiment and i can say that after Fast DC Charging when car was not locked the HV battery stay disconnected and you see these two warning lamps even if the CCS2 plug was removed from charging port and even if driver is sitting in driver's seat. You have to step on break pedal to move the car in READY mode and connect the HV battery to car's system.
I still think that this is weird behavior and i hope this issue was fixed in some firmware update (mine is R40).

The 12V battery warning is not about the battery voltage itself but indicates the charging circuit is not operational and so the battery is not being charged.

Evgen K · Jan 22, 2025

Martinonline said:
From the 'Fast Charging and Low Battery Warning' thread:

The 12v battery warning is not about the battery voltage itself but indicates the charging circuit is not operational and so the battery is not being charged.

You are right but there is small addition. If this lamp is flashing it's about low voltage of this 12V accumulator. According documentation (see second paragraph of details column):

Deleted member 2148 · Jan 25, 2025

Ian Key said:
Check the 12V battery terminals are tight.

You might need a software update as I thought the main traction battery should have kept the 12V battery topped up.

Only if car is locked.

Ian Key · Jan 25, 2025

Rattly said:
Only if car is locked.

Or you've sat on the driver's seat and pressed the brake pedal.

Sakuntala · Jan 25, 2025

wdryan2023 said:
Twice in the last few days, my MG4 seems to have "shut down" for no apparent reason.

This appears to have happened, on both occasions, when I didn't lock the car with the key fob when leaving the car.

The wing mirrors remain out, but it's completely 'dead' and can't even get in. No response at all and the app is not responding either.

The last time, it 'rectified' itself by the the next morning although I had to leave it in the local village overnght.

It's after happening again this evening in the driveway at home.

Any ideas what's happening here and now to resolve.

Thanks in advance.

I only had this problem everytime I use a water hose to clean the car. Especially when I soak up the side mirrors and front windshield. Power windows outside etc. I am suspecting that when moisture gets into the mirrors or windows exterior etc. Any short detected in the electric circuit due to moisture disables the side mirrors to open etc or unresponsive as you mentioned. Also the comments others mentioned about the 12 volt battery voltage capacity is a probable cause. In my case I wait a few seconds for the short circuit error to clear itself and retry until the side mirrors open up to regular mode. I just do several unlocks until the mirrors open up

Martinonline · Jan 25, 2025

Ian Key said:
Or you've sat on the driver's seat and pressed the brake pedal.

I'm sure that you only need to power up the car by sitting in the seat to get the 12V battery being maintained by the HV battery. You don't need to put the car into Ready mode by pressing the brake pedal unless, as reported in some cases, you have just finished DC charging.

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