Newly purchased MG5 battery module fault

[mgcars1]

hope someone on here can help??? Having purchased my new car from an auction site with an electrical fault which supposedly appeared after the 12V battery died, I have since replaced the 12V battery with a new fully charged one but have not been able to start the car. When switching on the ignition, the is an amber warning saying HV battery shut off. I have put the car on charge overnight using the domestic plug-in charger supplied with the car and it has charged to 97% on the display, but will still not start. I have tried the 12v disconnect to reset the system to no avail, the car is still displaying HV shut off message. Any ideas please?

 

[MickeySw]

Having purchased my new car from an auction site with an electrical fault which supposedly appeared after the 12V battery died.

The fact that the car charges is good news; the issue doesn’t seem to be the HV battery itself.
Best chance to get somewhere is trying to read/clear the DTCs with an OBD dongle and app (Car scanner or similar) as you have already done the ‘hard reset’.

 

[Verdigris]

Perhaps the HV battery is actually faulty. Have you got an OBD2 dongle and Car Scanner?

 

[maskull]

Maybe a stupid question , but are you putting the foot brake on while you're trying to start the car ? If not you will get the HV fault appearing

 

[CanyonReveller]

I'd recommend checking the voltage of the new lv battery disconnected from the car and then connected to the car after you've tried to start it. It should never go below 12v.

I viewed a pre-facelift 61kwh exclusive a while back that had some form of short circuit/ high drain across the 12v battery, so a new 12v battery would be discharged within a handful of minutes. It was advertised with a similar description and charging of the hv battery was still possible. I couldn't get the car into ready mode.

I came down to it possibly being a fault with the inverter not providing a voltage to replenish the 12v battery, but I couldn't be certain so walked away.

 

[MickeySw]

Maybe a stupid question , but are you putting the foot brake on while you're trying to start the car ? If not you will get the HV fault appearing

Good point.
Another idea, if your 12V aux voltage is low, the current will go up to compensate, might want to check your fuses…

 

[mgcars1]

Thanks for the above responses. I have had my diagnostic machine on the car but it wont communicate with any of the HV modules. Its probably too old and too basic for that, I had the AA out to it today and they found there was hard a fault stored in the drive motor.
During my own diagnosis I suspect there is a main fuse blown somewhere on the car (500 amp bolt on unit). There are several second hand ones for sale on ebay. From what I can see, I believe it is either in the HV battery box or housed in the top part of the drive assy. Has anybody here had similar issue with this fuse?

 

[Caramaddy]

This might be an obvious question, but has the car a full service history at MG? It would the be under warranty.

 

[Verdigris]

This might be an obvious question, but has the car a full service history at MG? It would the be under warranty.

I wondered that but I suspect the reason it is in the dog auction is because the service schedule hasn't been kept to, or it was a private hire vehicle and the limited warranty has expired.

 

[MickeySw]

From what I can see, I believe it is either in the HV battery box or housed in the top part of the drive assy. Has anybody here had similar issue with this fuse?

Most of the MG5s are still under warranty, therefore there is very limited DIY repair knowledge out there presently.

From experience with other EVs, I would guess that the fuse inside the battery box is fine (it’s charging). If you have a blown fuse then it’s more likely on inverter side.

 

[mgcars1]

I have read through the siac mg workshop manual for the MG5 and in the fault diagnosis for not starting , it mentions a fuse in the "PEB", which is the electrical box on top of , and part of ,the transmission assy. I am going to take a look at this tomorrow, and lift the lid, hopefully a fuse inside this module has blown. I will keep you updated on progress.

 

[MickeySw]

I have read through the siac mg workshop manual for the MG5 and in the fault diagnosis for not starting

How did you get your hands on that?

 

[Alibro]

Thanks for the above responses. I have had my diagnostic machine on the car but it wont communicate with any of the HV modules. Its probably too old and too basic for that, I had the AA out to it today and they found there was hard a fault stored in the drive motor.
During my own diagnosis I suspect there is a main fuse blown somewhere on the car (500 amp bolt on unit). There are several second hand ones for sale on ebay. From what I can see, I believe it is either in the HV battery box or housed in the top part of the drive assy. Has anybody here had similar issue with this fuse?

I'm not fully familiar with the fuse layout in MG5's but I'd have thought If the HV fuse was blown you would not be able to charge it. The fact you can would suggest something else is wrong.
But please be careful, when poking around anywhere near that fuse. With the battery charged there is 400V there and that is enough to kill you several times over.

 

[shpub]

I don't know what your experience or background is but so forgive me if this is a bit granny sucking eggs.

Just to confirm the system is full of 400v sources which if touched will kill you. You need the right ppe and to follow the procedures for isolating the battery. Assume nothing.

If the 400/500A fuse has gone I would not recommend simply replacing it and seeing what happens. Those fuses require a serious short to rupture - short out a battery or a couple of modules with molten spanner type short - and this can damage other parts of the car. There are also precharge resistors that allow the inverter capacitors to slowly charge and they are connected by a relay.

Either way DO NOT ASSUME that the fuse is not live even when the car is switched off and the MSD is disconnected. You do not know what is wrong with this car and should not assume anything.

That HV fuse is for the connection to the inverter and onto the motor. If it has blown then the most likely fault could be a motor or inverter fault. You need to track down what the fault code is that the AA reported.

The charger connects to the battery via another route. It cannot produce the 200kw that the big fuse is rated at and has a seperate protection circuit.

My experience is that those fuses rarely fail - they can - but usually it is one of the power relays, its drive circuits, or HVIL O/C or the line insulation monitor that stops the HV from being connected.

 

[mgcars1]

Hi I have quite extensive knowledge of EV technology having worked for a bus manufacturer who produced the first electric buses to operate in London, hence my training and experience with HV drive systems.
Getting back to my MG5, I attempted to remove the top of the PEB, but with all the bolts removed, the top housing would not come off. I think the whole drive motor assembly needs to be removed from the car to allow this part to be removed, which I don't have the facilities to do. It looks like the car is going to have to go into a dealer workshop for repair. According to the AA engineer, there is a massive backlog at most MG dealer workshops so not Ideal.
As for the workshop manual, I purchased online from eBay. The only thing I don't have is wiring diagrams for the car.

I don't know what your experience or background is but so forgive me if this is a bit granny sucking eggs.

Just to confirm the system is full of 400v sources which if touched will kill you. You need the right ppe and to follow the procedures for isolating the battery. Assume nothing.

If the 400/500A fuse has gone I would not recommend simply replacing it and seeing what happens. Those fuses require a serious short to rupture - short out a battery or a couple of modules with molten spanner type short - and this can damage other parts of the car. There are also precharge resistors that allow the inverter capacitors to slowly charge and they are connected by a relay.

Either way DO NOT ASSUME that the fuse is not live even when the car is switched off and the MSD is disconnected. You do not know what is wrong with this car and should not assume anything.
U046181
That HV fuse is for the connection to the inverter and onto the motor. If it has blown then the most likely fault could be a motor or inverter fault. You need to track down what the fault code is that the AA reported.

The charger connects to the battery via another route. It cannot produce the 200kw that the big fuse is rated at

and has a separate protection circuit.

My experience is that those fuses rarely fail - they can - but usually it is one of the power relays, its drive circuits, or HVIL O/C or the line insulation monitor that stops the HV from being connected.

1B2500, unknown fault code was the stored fault for the drive system.The AA engineer couldn't get any info on the fault.
The only other fault which wouldn't clear was an abs/ stability fault code U041681, but the engineer thought that this might clear once the car was driving. Looks like it's going to have to go into a MG workshop for diagnosis.

How did you get your hands on that?

Purchased via ebay

 

[RichP]

I wish you the best of luck getting this repaired. My 14 month old MG5 was replaced by the dealer as neither they or MG UK could fix the problem after >6 months of trying. I’m not saying the HV battery was the cause but it was constantly disconnecting the HV battery and throwing up multiple error codes.

 

[MickeySw]

Getting back to my MG5, I attempted to remove the top of the PEB, but with all the bolts removed, the top housing would not come off. I think the whole drive motor assembly needs to be removed from the car to allow this part to be removed, which I don't have the facilities to do.

I have seen it on my 1st Gen EV that in addition to bolting lids, a sealing compound is also used which acts like glue, a heat gun can work wonders..

 

[shpub]

1B2500, unknown fault code was the st
ored fault for the drive system.The AA engineer couldn't get any info on the fault.
The only other fault which wouldn't clear was an abs/ stability fault code U041681, but the engineer thought that this might clear once the car was driving. Looks like it's going to have to go into a MG workshop for diagnosis.

1B2500 is not a valid code or at least it is not one in the MG5 manual. It could be an incorrect decoding from the OBD reader. There is a PID2500 which is an internal PEB fault with the electronics supply voltage. It may be that.

Given that the 12v battery died indicates that the Charger may have failed to keep the battery charged that would indicate that the CCU is faulty. However it could also be caused by the HV battery not connecting due to some other fault without which the CCU cannot charge the 12v battery or provide the power for the HV battery heater.

U041681 is a comms issue between the power steering control and stability control system indicating that no valid messages have been received after 1s. Can't be cleared until the 100 consecutive valid frames are sent and/or 40 failure power on/off cycles. Whether this is a knock on effect from other failures I don't know. It is a shame that the AA man didn't note the codes that he could clear as that would have given a lot more information.

Assuming that 1B2500 is what I think it is, I'm guessing that there has been a major voltage spike or short that has taken out several of the modules. This should be covered under warranty unless the car was an ex taxi. This raises the question of why the previous owner(s) didn't do this.

 

[mgcars1]

A quick update , the car was collected by the AA and taken to the nearest MG dealer. They have diagnosed the steering column lock module as the fault. Part has been ordered and should be fitted Tuesday/Wednesday and hopefully that will be it!!
I'll update once the work is complete

 

[JonCott]

The fact that the car charges is good news; the issue doesn’t seem to be the HV battery itself.
Best chance to get somewhere is trying to read/clear the DTCs with an OBD dongle and app (Car scanner or similar) as you have already done the ‘hard reset’.

My MG5 was dead recently when we were on our way out. Only had it about 2wks. Used the key to get in and the bonnet open and charged the 12v battery even though it was showing over half. Thought I'd try the warranty and booked into MG dealer. Half a day later 'All done. We've run a bulletin update from MG. Basically turns off the traction battery and back on. It is a recorded issue. Should fix it. But if it happens again bring it back.' Might be worth trying?