Fault codes in drive battery

[kennypats]

I have bought a broken 2010 IMIEV. Found a problem with the obc and did this repair. then cleared all fault codes. Now left with these 3 fault codes

P1A33 - cell voltage sensor (BMU)
P1A39 - charge state signal error (BMU)
U1924 - Bat -Lin bit error

Looking like a fault in CMU board number 3 and one cell in that package, cell number 17 reads a low voltage of 2.51 V

Some suggestions on the repair process would be appreciated, viewing that it will require the removal and reinstallation of the drive battery. I want to ensure I do the job right, as it is a major undertaking just to remove/reinstall the battery in itself.

 

[MickeyS70]

Hello

You’re right 2.51V is way too low for a cell but it’s not unheard of that the voltage isn’t correctly reported by the CMU.

Have a look at this excellent video below (post #46) regarding battery removal

https://myimiev.com/threads/battery-pack-change-plans.5525/page-3

 

[kennypats]

Thank you for that link.

I guess my main concern is verification of the CMU board in pack 3 and finding a couple of used cells for replacement of the low voltage one.

 

[MickeyS70]

Thank you for that link.

I guess my main concern is verification of the CMU board in pack 3 and finding a couple of used cells for replacement of the low voltage one.

See below for diagram
https://myimiev.com/threads/hv-battery-pack-layout-diagram-and-cell-numbering.5160/

What is the remaining capacity of your pack? As decent LEV50s are hard to find you may get away using NMC 93Ah or similar instead.

If the fault is caused by the CMU you may be able to replace the LTC chip.

 

[piev]

Thank you for that link.

I guess my main concern is verification of the CMU board in pack 3 and finding a couple of used cells for replacement of the low voltage one.

I have cells if you need some. I am in Alabama.

 

[Gary12345]

2.51v is the default shown when the value received from the cmu is out of range. The cell voltage is reported in a few places, some will show the true reading - check in the cmus, bmu and ev-ecu. Also check adjascent cells as you can usually spot a measurement fault vs a cell failure that way. Cheers

 

[kennypats]

I have cells if you need some. I am in Alabama.

Thanks for the offer, but hope to find them here in New Zealand. Shipping them from the USA would be expensive.

 

[MickeyS70]

2.51v is the default shown when the value received from the cmu is out of range. The cell voltage is reported in a few places, some will show the true reading - check in the cmus, bmu and ev-ecu. Also check adjascent cells as you can usually spot a measurement fault vs a cell failure that way. Cheers

Actually if the CMU reports back 0 (no data) the BMU would interpret this as 2.1V therefore 2.51V is quite plausible and I wouldn’t point the finger at the CMU just yet. Did you check the reported cell temperatures, any outliers on CMU3? I have seen examples where just one weak cell was taking down the whole pack.

I assume the car doesn’t charge any longer because of the faulty cell? There may be a way to get around that to do further troubleshooting but to do a permanent fix, the battery will need to come out regardless.

 

[CZeroOwner]

Actually if the CMU reports back 0 (no data) the BMU would interpret this as 2.1V therefore 2.51V is quite plausible and I wouldn’t point the finger at the CMU just yet. Did you check the reported cell temperatures, any outliers on CMU3? I have seen examples where just one weak cell was taking down the whole pack.

I assume the car doesn’t charge any longer because of the faulty cell? There may be a way to get around that to do further troubleshooting but to do a permanent fix, the battery will need to come out regardless.

To supplement Mickey, the formula for converting the bytes on the the CAN network to cell voltage is:

volts = (6E1[4] * 256 + 6E1[5] + 420)/200 This is the voltage for cell A in module 1. 6E1 is the PID and [4] means byte 4.

If both bytes are zero then the voltage shown is 2.1.

However data from Ionysos, who has converted his battery to CATL NMC 93 cells, show that when there were faults the voltage reported by the BMU was 2.51. In Ionysos' case these failures occured only when the voltages of the cells prior to failure were between 2.975 and 3.25 volts. Furthermore the failures were only in module 3 cells A - H and module 4 cells E-H. These are new cells, their true voltages were low but not too low and they were clustered together so I believe this was a CMU failure and not a problem with the cells.