The only modes the heating is actually working (not just blowing air around) is when the car is READY to drive or during the preheat function via the app (car locked).
It’s highly recommended to externally charge even a brand new 12V aux overnight as you don’t know how long it’s been sitting on a shelf.
The car will shut down immediately once the 12V aux goes below a certain limit (11.8V is too close for comfort imho), regardless of the SoC of the main battery.
The CCU (Combined Charge Unit) in a MG5 has two functions:
provide low voltage power (14V ish) when driving or charging
convert AC mains voltage into DC battery voltage during Type1/2 charging
You’re correct, it certainly looks like the CCU is defective (or fuse ‘M’ under the hood has blown)...
It looks like the car successfully balances the cells in an hour and a bit.
Can you confirm that all looks good when you turn on the car, e.g. the message only pops up when reversing?
This could indicate that (at least) one cell’s voltage drops significantly under load (car moving) and...
If yours is a long range model, then a reported SoH of 98% seems (given the age and mileage) excellent as in ‘too good to be true’.
If it’s a standard range, it could be more realistic if it has one of these rumoured ‘reject LR battery’ fitted.
The ‘tortoise mode’ could be caused by either a...
‘Snail mode’ is a condition where the car limits the available power to prevent damage. A very common one is when a cell voltage drops below a safety limit which seems to be the issue here.
A functioning car will let you fully discharge the battery before snail mode is eventually activated.
Moving the steering wheel fully left & right should clear all the errors that will appear after re-connecting the 12V aux, otherwise driving a few yards should do the job..
It’s rare, but I have heard of MG5’s suffering from what appears to be a voltage imbalance caused by a weak cell.
I would start with a hard reset, I.e. disconnect the (-) pole of the 12V battery for a few minutes.
If that doesn’t make a difference, invest in a OBD dongle and check the cell...
That’s odd, the book value of 250 miles should not be exceeded @100% SoC after a reset of the accumulated total?
I wouldn’t worry about it though, as it reverts back to 240 after a driving few miles.
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