SME battery management faulty.

[SeanL]

Hi. I've followed this forum for a while and am very impressed with the breadth of knowledge and good advice shown here.
I hope you can help me with an SME question.
My local BMW authorised workshop tells me the SME needs replacing because it shows error codes.
I asked what the consequences would be if i don't replace it, but they could not answer that question.
So, can anyone in this group help me - would it be dangerous to continue driving if the SME fails completely?

 

[frictioncircle]

Welcome to the forum, SeanL!

By "SME battery", do you mean the auxiliary 12V battery up front?

 

[MagicCarpet]

The SME is within the HV battery and is the cell management electronics.

I guess it will be expensive to look at and wonder if fully charging the battery at least 3 times might help ensure the battery management system can correctly balance the cells - this process wont happen if the car is not at full charge every so often.

If error codes persist it may be a cell fault in the HV battery. Cell faults have a long warranty but there is a dealer cost to test for this.
A guide is to go into the service menu and take a reading of Batt kappa max especially if you have done this check in the past,
or verify if your range has become significantly lower than it used to be

 

[alohart]

I guess it will be expensive to look at and wonder if fully charging the battery at least 3 times might help ensure the battery management system can correctly balance the cells - this process wont happen if the car is not at full charge every so often.

Cell charge level balancing doesn't occur when charging is active, so repeatedly charging the battery pack won't affect the passive cell balancing used by the BMS.

Over more than 8 years of ownership of our 2014 BEV, I have only occasionally charged to 100%. Our i3 has been driven only 12k miles, so it has sat parked for most of its life which is when passive cell charge level balancing occurs. The mi3 app shows that the maximum and minimum cell voltages differ by only 0.004 V at a 100% displayed charge level indicating excellent cell charge level balance. At 0.5% displayed charge level, the maximum and minimum cell voltages differ by only 0.025 V, and the maximum and minimum cell capacities differ by only 0.25 Ah indicating that all cells have similar capacities and charge levels. This is evidence that cell charge level balancing occurs even when the charge level is less than 100%.

 

[SeanL]

Hi everyone. Thanks for your excellent, in depth replies.
It is the high-voltage cell management system that is giving errors.
One answer i might have missed: is there a safety issue if the BMS fails completely?
Here are answers to some of your points:
I regularly charge to 100%, but still have error codes.
I've been checking Batt kappa max values regularly since i noticed a deterioration in range in 2018. I reported this to the dealership but they refused to accept there was a problem. The capacity was still above the threshold for warranty to kick in.
I then reported again in 2021, when Batt kappa max was down to 14.3kwh. The range has dropped commensurately to about 55miles. It was regularly at 100 miles when I purchased the car in 2015.
This doesn't necessarily mean there's a fault in the high voltage cells. It just means the BMW workshop can't detect any cell faults until the BMS is replaced.
BMW refuse to acknowledge there is a problem, so have washed their hands completely.
Maybe its time to move the car on to a different owner.

 

[frictioncircle]

SeanL –

(the following assumes you're in The States)

Have you just dealt with a single dealer for this issue? If so, ask them to escalate your complaint – tell your dealer's Service Advisor that you want their Area Manager to evaluate your situation.

If they decline, contact your area's BMW Area Manager directly. BMW NA's email format isn't difficult to figure out and a quick search of "BMW Area Manager" along with where you're located should return helpful LinkedIn results.

If all of that fails, bring your issue to BMW NA's social media channels.

Personally, I couldn't consider selling to a private buyer a vehicle with such issues as you describe unless I first exhausted all the above options and then made sure the private buyer was well aware of the state of the battery.

 

[MagicCarpet]

seems to me it would be worth the cost of having the battery capacity degradation check done

If the dealership can charge and discharge the battery and measure better than 70% of new capacity then you will have more than 70 miles range.
the range you currenty have seems well short of the spec.

If they cannot, they must replace the battery pack as it is faulty - its not your problem the SME is reporting errors - presumably cell errors.


Alohart mentions the Mi3 app to check what the BMS (the SME) is reporting differences in individual cell max. and min. voltages
the results could be a giude for yourself to decide what the likelihood of cell faults might be

 

[SeanL]

Thanks for all the advice. I'm actually in the UK. I contacted the CEO of BMW UK, but they have refused to help.
Thanks for letting me know about Mi3 Alohart and MagicCarpet. I'll certainly give this a go. Thought I'd also try Bimmergeeks ProTool.
Just to reassure FrictionCircle I would not sell without alerting the buyer to problems with the BMS.
The problem with charging to get, say, 70 mile range, is that this is not really 70 miles. There's a rapid deterioration in range as I drive (Eco+ on and driving style is economica). So, 70 miles becomes only 55 mile range.