Full charge and range, but bars go to 0 and turtle mode on [RESOLVED]

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New member
Apr 30, 2023
Hi everyone,
I've had a 2012 i-Miev for almost 5 years now and am very pleased with it.

Yesterday out of the blue I went on a short 3 mile trip with a full charge. Half way through the bars dropped to nothing, I got the car with the exclamation, turtle mode and regen braking stopped working. The range was still showing healthy. The weather was almost 20 degC so not cold at all.

If I continue to drive the bars come back (but still exclamation mark and no regen braking), then go away again after a minute or so.

If I stop the to car and remove the key from the ignition, then restart, it works fine for about a minute or so, then happens again.

This happens even if all I do i cruise down a mild slope (ie happens even when not under load).

When I try to charge the car initially it shows charging and I can hear the cooling pump, but after a minute or so the charge stops and I get the exclamation car again.

I don't know of any EV mechanics near me and I am loath to take it to the main dealer (who has been servicing the car so far) as I fear dealers often give terminal diagnostics for older cars!

Any ideas?

Thanks in advance,
ElectricIggy said:
Any ideas?
My wild guess: an intermittent connection from cell to CMU (cell management unit). Perhaps an SMD fuse or resistor, or a loose bolt, broken PCB track, or cold solder joint.

Alas, the CMUs are buried in the high voltage battery container, so it's highly non-trivial to even get to them. Few people do board level repair, and fewer yet have stocks of refurbished CMUs sitting on the shelf ready to go.

It might also be one of the ECUs, either the BMS or VCU ECUs (Battery Management System or Vehicle Control Unit Electronic Control Units). Or the wiring thereto.

The only user accessible thing to try would be to see if the wiring harness has been disturbed under the car, especially near where the signal cables plug into the battery (there are about 3 from memory). Or the wiring harness that connects to the ECUs under the rear seat. It could be something obvious, like some animal chewed a wire.

Another thought: perhaps it's just in need of battery balancing. There is a "smoothing charge" procedure that dealers should be able to perform. Unfortunately, I have no idea of its effectiveness, and whether it has a realistic chance of helping in your specific case.

I am loath to take it to the main dealer (who has been servicing the car so far) as I fear dealers often give terminal diagnostics for older cars!
Well, sorry to say, but a failing cell is another possibility. 2012 EVs (I have a 2012 Leaf myself) are likely to have tired cells unless they have been replaced.

EVs are generally pretty reliable, but when there is a failure like this, it can require a fairly well clued repairer to sort it out. Unfortunately, there are way too few of those about at present. Sorry I don't have more cheery news; perhaps someone else can think of something I've overlooked.
Hi Iggy
Sorry to hear about your troubles, unfortunately without diagnostic codes it’s a bit of a guessing game as to what the issue(s) could be.

To make a start, make sure your 12V aux battery is in good condition and fully charged.

If you don’t trust your dealer then you need to get yourself an OBD dongle and use one of the free apps to troubleshoot.

Link below gives a good overview

Thanks guys, I always feared this day would come - I can tinker around OK with IC engine cars but when I got my I-Miev I was worried what would happen if I had a fault I couldn't resolve!

I'll have a poke around at the suggested locations, my gut feel is that a loose connection/faulty connection could be the culprit given the intermittent nature of it... still that fault could be in 100 different locations!

It's not so much that I don't trust the main dealer, it's more that, as coulomb has said, I feel this needs good troubleshooting repairer and dealers tend to just swap out entire components. I haven't changed any cells but if I'm told it needs a new battery the car could be a write off, which I don't want...

Pardon the ignorance but in terms of OBD dongles, there's a huge selection online with vastly different price ranges. Any idea if these make a difference, or are they just an interface and it's the apps that matter?

Thanks again, I'll keep you updated
What is the age, status and condition of the 12V battery? a weak, old or worn out 12V can cause this issue and a multitude of other faults. Check, verify and correct if necessary to rule out this as a culprit.

The other culprit might be a weak or worn out cell in the HV pack. This could be found using an OBDII dongle and one of the phone apps.

i've had good service with the biuetooth radio of OBDLink LX dongle and an android phone device using the Canion app. About $50, beware of counterfeits, it is a scantool.net device.
For a wired device i use one that has reset feature for most DTCs. It was about $100 at the time, don't have it in front of me right now for the model number.
Hello all,
Many thanks for the replies, it's been really helpful. Although GUIDO is not yet back on the road, the problem has been located and is awaiting repair.

In the end I had 2 main issues:

1) Where to find a reputable mechanic to fault find and fix a 10+ year old EV?
After a fair bit of researching and calling around I landed on HEVRA.ORG.UK (Hybrid and Electric Vehicle Repair Alliance Ltd.) which led me to a great local guy, who actually diagnosed (well, educated guess!) the fault over the phone (later confirmed via diagnostic tool).

2) What was the fault and was it terminal?
A diagnostic revealed a faulty voltage sensor on the CMU of battery module 5 - exactly what coulomb suggested it could be 👍 top man! 😉 Clearly with 'faulty' data on one of the battery units the car was going into safe/limp mode and refusing to charge given the unknown status of one of the modules.
Not a cheap repair - HEVRA harvest old/broken boards and send them off to get refurbished and supply repaired boards to their network,. After parts and almost 2 days labour to get to the part the estimate is at least £1,100.

Given the value of the car is far more if it's driveable I didn't hesitate to pay for the repairs, but I guess it does make me wonder at what stage I will deem it better to move the car on rather than have the potential of a costly failure. Given the stupidly high cost of cars (new and second hand, EV or IC) I still think it's worth holding on to. Plus I love my little Guido!

I'd be interested in knowing people's views on longevity of ownership/whether there comes a stage that it's best to sell on a working older car rather than a non-starter for scrap parts and just run it into the ground...
Great to hear Guido will be on the road again soon.

I have replaced a CMU board with the aid of a car lift DYI style in a day, second hand part cost me less than €100 a year ago, but you’re right beggars can’t be choosers.

I intend to run my ‘bug’ for as long as I can and then use the battery for solar storage once D-day comes.

On the other hand you will never get a better trade-in price if you decide to upgrade soon. Personally I would be a bit worried having to rely on a 10 year old Imiev for my sole mode of transport as any small issue could put it off the road permanently due to lack of spares or donor cars in the years to come…