MG5 (FL) 12V Battery Drain

[Waggers66]

Hello all,
Interesting 12V problems... I seem to have had all of them since buying my 72 reg MG5. So, long story short:-
1. MG battery replaced by good reliable battery
2. Less occurrence of voltage drops
3. Longer journeys (100+ miles) 12V drained right down. On one occasion complete shut down on M40, frightening!
4. Became very adept at whipping 12V battery in and out to charge externally!
5. Asked MG Hendy Crawley to investigate, made appointment... TWO MONTHS wait!!!
5.5 Explained to technicians my theory that 12V was charging ok when car itself was being charged but NOT charging whilst driving via the HV battery. See below, they agreed after the diagnostics.
6. Went in two weeks ago. Did full diagnostic. They think it needs a new CCU.
7. They have sent a 'Snowcase' ?? to MG and asked for a replacement part (£1200?)
8. MG seem to be reluctant to replace, asking Hendy to do more tests?
9. Meanwhile they can't give me a courtesy car and show no sign of getting a resolution.
10. Other potentially useful info. The display screen occasionally glitches out, going green and stripey.
Well that's my current tale of woe. I'd be interested to hear anyone else's experience. Plus any advice about contacting MG direct??

 

[MickeySw]

3. Longer journeys (100+ miles) 12V drained right down. On one occasion complete shut down on M40, frightening!

When in READY all 12V systems are powered by the CCU, therefore you’re right, it’s not a battery problem

5.5 Explained to technicians my theory that 12V was charging ok when car itself was being charged but NOT charging whilst driving via the HV battery.

Did you measure the 12V battery current or how do you know it works when the car charges?
It does seem strange that the DC/DC section only fails when driving but the only way to rule out the CCU as the cause is to replace it.

See below, they agreed after the diagnostics.

Surprised that the garage didn’t figure this out immediately, simple way to check, with the car in READY just disconnect the 12V aux and wait..

Well that's my current tale of woe. I'd be interested to hear anyone else's experience.

CCUs have been replaced under warranty for other drivers, usually due to the car not being able to AC charge.

9. Meanwhile they can't give me a courtesy car and show no sign of getting a resolution.

That’s usually down to MG dragging their heels to accept this to be a warranty issue

Plus any advice about contacting MG direct??

Most drivers in your situation have reported this to be an “utter waste of time” but I’d email them anyway if only to have a paper trail..

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[Waggers66]

Thanks Mickey