MG5 Dcdc charge fault??

[trehans]

Hi, bought my 21 MG5 prefacelift a few weeks ago, 15000 miles. Everything was going smoothly but today got a scare while driving when a warning message appeared - DCDC charge fault with a red battery symbol.
Car was at 78% charge and this warning appeared a few times before arriving home.
Anyone had any experience with this?
Help would be greatly appreciated.
Thanks

 

[maskull]

Not had that . If it's a few weeks old return to the dealer is best .

 

[Jomarkh]

What was the 12V battery level showing?

 

[Alb]

Not a common fault.
The logs will need to be interrogated by a dealer to get more info.

 

[MickeySw]

The only DCDC action happening while driving is the charging of the 12V aux from the HV battery via the CCU. That’s why looking at the 12V aux level as suggested by Jomarkh is important.

[Edit] above is actually not the full story, a working DC-DC will provide all low voltage power (including charging the 12V aux) to the car..

When the car is in Ready it should show a stable value around 14V, if it’s way below that or fluctuating the issue is more likely a faulty DC/DC. Suspect the 12V battery, if the car fails to go ready (these are known to fail and come with just 1 year warranty anyway)

Keep an eye on it otherwise and if it happens again bring it back to the dealer.

 

[trehans]

What was the 12v battery level showing?

Where do I find this?
Display shows 14.1V sometimes drops to 13.7 if that helps

The only DCDC action happening while driving is the charging of the 12V aux from the HV battery via the CCU. That’s why looking at the 12V aux level as suggested by Jomarkh is important.

When the car is in Ready it should show a stable value around 14V, if it’s way below that or fluctuating get a new battery (these are known to fail and come with just 1 year warranty anyway)

Keep an eye on it otherwise and if it happens again bring it back to the dealer.

The only DCDC action happening while driving is the charging of the 12V aux from the HV battery via the CCU. That’s why looking at the 12V aux level as suggested by Jomarkh is important.

When the car is in Ready it should show a stable value around 14V, if it’s way below that or fluctuating get a new battery (these are known to fail and come with just 1 year warranty anyway)

Keep an eye on it otherwise and if it happens again bring it back to the dealer.

What battery is recommended?

 

[maskull]

Where do I find this?
Display shows 14.1v sometimes drops to 13.7 if that helps

14 volt ,13.7 when lighting in use looks OK . Maybe it was a false warning. I would still take it to the dealer to have it checked and logged .

 

[RichP]

I’ve had similar but in addition to the dcdc charge fault, I also got auto hold fault and most recently motor fault. The car also either shuts down or goes into limp home mode. This first happened on the 3 June and 4 breakdowns and 6 months later the fault remains undiagnosed and I’m left without a car! I hope you have better luck.

 

[Richierich37]

Hi, bought my 21 MG5 prefacelift a few weeks ago, 15000 miles. Everything was going smoothly but today got a scare while driving when a warning message appeared - DCDC charge fault with a red battery symbol.
Car was at 78% charge and this warning appeared a few times before arriving home.
Anyone had any experience with this?
Help would be greatly appreciated.
Thanks

Hey, did you ever get the DCDC CHARGE FAULT fixed?

 

[decrep]

There's a very similar thread here. the fix was dealer replaced car. Maybe not that uncommon.

 

[Richierich37]

There's a very similar thread here. the fix was dealer replaced car. Maybe not that uncommon.

Cheers, I’ve had a look and my car is getting lifted tomorrow and delivered to the EV garage for diagnostics and hopefully fixing!

 

[Richierich37]

I’ve had similar but in addition to the dcdc charge fault, I also got auto hold fault and most recently motor fault. The car also either shuts down or goes into limp home mode. This first happened on the 3 June and 4 breakdowns and 6 months later the fault remains undiagnosed and I’m left without a car! I hope you have better luck.

I got the car lifted and recovered to MG, £320 to diagnose the fault and confirmed it’s the CCU (onboard charger) that needs replacing so my total bill is £2773 and they’ll be working on it next week once the part arrives! Car is nearing 3 years old but has covered 98k miles as I’m a Private Hire. Hopefully it can do another 98k and nothing else at that price blows!

 

[dragon2611]

14 volt ,13.7 when lighting in use looks OK . Maybe it was a false warning. I would still take it to the dealer to have it checked and logged .

Seems a bit low, My 12V battery is getting as low as that, used to be around 14.5 and 13.9 (depending if headlights are on) I suspect it's on it's way out and needs changing.

Particularly as when I drove it shortly after charging the HV battery overnight it was at around 14.5v yet drove it later in the day and the 12V was just at 14.0/14.1v with the dcdc running.

Also see a 0.1v drop on the reading if breaking/turning (load from the rear brake lights + power stering probably)

 

[Alb]

When the DCDC converter is running, you are reading converter output voltage, not battery voltage.

 

[dragon2611]

When the DCDC converter is running, you are reading converter output voltage, not battery voltage.

Which still reads higher if the battery is more charged and drops with load...

Also it's the overall 12V system voltage afaik. not specifically the DC-DC output voltage.

 

[Coulomb]

Also it's the overall 12V system voltage afaik. not specifically the DC-DC output voltage.

The DC-DC converter is very strong, capable of well over 150 A when needed. So when the DC-DC converter is operating, the only difference between the DC-DC output voltage, the 12 V battery voltage, and the "12V system voltage" is due to voltage drop across the wires. Usually the wire from the DC-DC converter to the battery is quite thick, like about 10 mm² (edit: possibly 25 mm²), so the voltage drop would be quite small unless the loads are extremely high.

So when the DC-DC converter is operating, the battery voltage meter is essentially reporting the DC-DC output voltage.