MG4 dead after charging (disco lights)

[Papagato]

I charged my 2023 MG4 Luxury at work today in the nice cool underground car park.

When I returned, it unlocked but the mirrors remained folded. When I sat in it and pressed the brake it didn't start but all the lights just went crazy. Interior, headlamps, rear and brakes, all flashing away at a few hertz. Out of synch too, not all at once.

After a while it died down and lower brake lights are on and flickering and the speedo screen backlight flashes every few seconds. Nothing works, of course.

Any advice or simple fixes while I wait for the tow truck?

 

[mystreet]

If you have a 10mm spanner, disconnecting the battery for about 10 minutes. Reconnect it, computer reboot.

 

[webhiker]

12V battery collapsed?

 

[Papagato]

If you have a 10mm spanner, disconnecting the battery for about 10 minutes. Reconnect it, computer reboot.

Very close!

The 12V was flat. Quick boost and we're good! The mechanic said it doesn't charge unless the car is in use, "Ready" on the dash.

 

[siteguru]

It should charge automatically, even when the car is Off. But there's a minimum state of charge (SoC) below which it won't do so ... received wisdom is that this SoC level is as high as 50% for some strange reason. (The manual tells us about this, but doesn't specify the SoC).

 

[mystreet]

Very close!

The 12V was flat. Quick boost and we're good! The mechanic said it doesn't charge unless the car is in use, "Ready" on the dash.

View attachment 37571

Time to get one of these then.

Amazon.co.uk

 

[Papagato]

It should charge automatically, even when the car is Off. But there's a minimum state of charge (SoC) below which it won't do so ... received wisdom is that this SoC level is as high as 50% for some strange reason. (The manual tells us about this, but doesn't specify the SoC).

I think if the car is charging, the HV battery is isolated from everything else, so won't charge the 12V.

 

[Papagato]

So the ANWB man said there have been a few problems like this recently. If the computer decides to consume a load of power, it can drain the 12V battery in a few hours.

So I'm going to blame the new app update, which seems to never actually fully connect, but constantly tries.

This weekend I have to go away, I'll be digging out the old jump cables from when I owned a Volvo. Just in case.

 

[lordsnipe]

I'm pretty sure the 12V lead acid battery is also charged when the car is charging... not sure why it would be flat whilst plugged in.

 

[Ian Key]

I'm pretty sure the 12V lead acid battery is also charged when the car is charging... not sure why it would be flat whilst plugged in.

From what I remember (long story as mine is still at the dealers with a charging fault) the 12V battery is charged when the car is charging on AC but not on DC.

 

[Martinonline]

The thread 'MG4 Unresponsive' discussed 12V battery charging. @Coulomb posted that he could see no reason for the low voltage battery not to be charged whilst DC charging. Another poster in a different thread (can't find it) supplied an image of the low battery voltage levels over time when DC charging which indicated the battery was being charged until DC charging stopped and then restarted when the car was powered up after DC charging.

 

[Martinonline]

Found it here:

Looking at my data history I can see my 12 V battery at >14 V during a DC charge session. e.g. this brief DC charge session:

View attachment 37201

The orange lines are data samples taken every couple of minutes of the DC drive system power (negative = charging), the white dots are samples of the auxiliary 12 V battery voltage, which was sitting at 14.1-14.2 V, tailing to 13.8 V at end of session. Aux battery dropped right down immediately after charging stopped, then came back up again when I started to drive away.

I see this pattern repeated in the data for other DC charge sessions.