MB87
Novice Member
Written 7th May 2024
Recently bought used MG5 61.1kWh 72 plate with just over 7k miles.
I had intermittent Check HV battery coming on the dashboard with the car going into limp mode on three occasions.
The car seems to be sorted now but here are the details and symptoms just in case it helps someone.
Symptoms
Intermittent “Check HV battery” red warning sign was coming on dashboard and it would clear by itself. Sometimes it would be on the dashboard for a few seconds and sometimes for longer. It didn’t have any particular pattern e.g. appearing after charging, at particular battery percentage, type of charger used to charge it etc.
When the light would be present it did not affect driving experience whatsoever.
I didn’t notice that the battery heater setting in the car settings could not be switched on.
The car went into turtle mode twice after charging but after a few miles and once randomly on the motorway. Not a pleasant experience. If the car goes into a limp mode whilst stationary or if you stop when it goes into the limp mode you can’t drive more than 10mph. If you’re on motorway I kept going with my foot down, the car was slowly loosing speed but it did get me to the next junction. By the time I reached the slip road I was on 40mph.
The limp mode would clear itself however the car was underpowered for the next few miles.
I tried several things such as draining the battery to 10% and then charging it for 12h but nothing happened. I did get a few more miles range though after doing it.
Dealership and resolution
I took my car to MG Dealership in Oxford after the first limp mode and they were very methodical with their approach.
They firstly found a bunch of historic codes but no active codes. As there were no active codes on the computer they deleted/cleared the historic ones and sent me off.
The following day the “Check HV battery” warning appeared again and it was very frequent, such as every time I’d drive the car.
The dealership booked me in but I had to wait for few weeks as their technician was on holiday and they had no bookings.
In the meantime the car went the second two times into the limp mode. Once when joining motorway (very unpleasant) and second time whilst on the motorway. This was on two separate days. I didn’t feel safe driving the car so took it to the same dealership and left it there until it could be looked at.
As I said, the technician was then very methodical and worked with MG HQ on the resolution.
He found that there might be a problem with one battery cell which wasn’t charging and discharging properly. My understanding is that he then had to keep the car on charger for 24h then discharge to 10%, then put on charger again for 48h.
Finally, working with the MG HQ they found that it was a software issue. The battery charging and discharging parameters were outside the tolerances and this was triggering the computer.
The software update was released and since then the car has been working fine.
The overall driving experience has changed for the better as it’s more consistent.
The battery heating system can now also be turned on.
I hope this helps someone.
Recently bought used MG5 61.1kWh 72 plate with just over 7k miles.
I had intermittent Check HV battery coming on the dashboard with the car going into limp mode on three occasions.
The car seems to be sorted now but here are the details and symptoms just in case it helps someone.
Symptoms
Intermittent “Check HV battery” red warning sign was coming on dashboard and it would clear by itself. Sometimes it would be on the dashboard for a few seconds and sometimes for longer. It didn’t have any particular pattern e.g. appearing after charging, at particular battery percentage, type of charger used to charge it etc.
When the light would be present it did not affect driving experience whatsoever.
I didn’t notice that the battery heater setting in the car settings could not be switched on.
The car went into turtle mode twice after charging but after a few miles and once randomly on the motorway. Not a pleasant experience. If the car goes into a limp mode whilst stationary or if you stop when it goes into the limp mode you can’t drive more than 10mph. If you’re on motorway I kept going with my foot down, the car was slowly loosing speed but it did get me to the next junction. By the time I reached the slip road I was on 40mph.
The limp mode would clear itself however the car was underpowered for the next few miles.
I tried several things such as draining the battery to 10% and then charging it for 12h but nothing happened. I did get a few more miles range though after doing it.
Dealership and resolution
I took my car to MG Dealership in Oxford after the first limp mode and they were very methodical with their approach.
They firstly found a bunch of historic codes but no active codes. As there were no active codes on the computer they deleted/cleared the historic ones and sent me off.
The following day the “Check HV battery” warning appeared again and it was very frequent, such as every time I’d drive the car.
The dealership booked me in but I had to wait for few weeks as their technician was on holiday and they had no bookings.
In the meantime the car went the second two times into the limp mode. Once when joining motorway (very unpleasant) and second time whilst on the motorway. This was on two separate days. I didn’t feel safe driving the car so took it to the same dealership and left it there until it could be looked at.
As I said, the technician was then very methodical and worked with MG HQ on the resolution.
He found that there might be a problem with one battery cell which wasn’t charging and discharging properly. My understanding is that he then had to keep the car on charger for 24h then discharge to 10%, then put on charger again for 48h.
Finally, working with the MG HQ they found that it was a software issue. The battery charging and discharging parameters were outside the tolerances and this was triggering the computer.
The software update was released and since then the car has been working fine.
The overall driving experience has changed for the better as it’s more consistent.
The battery heating system can now also be turned on.
I hope this helps someone.
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