openinverter forum

hi all, i need some help, i'm not used to working with E.V's but a friend asked me for some help, he bought a 2018 ioniq with a bad motor, it blew the capacitor in the inverter and apparantly the whole board is fried, he bought a replacement but when installed immo error comes up, he's asked me if it's possible to clone the replacement but i honestly have no idea if it's even possible, any help or suggestions are welcome, i've posted some pic's,

https://postimg.cc/1gQ3zzBQ
https://postimg.cc/Jt27kxKR
https://postimg.cc/7GQ4SP3h
https://postimg.cc/LJBMN3kS

The guys on german goingelectric forum did this, by using the CPU board of the original car in the exchanged inverter.
An other option could be to read out the two controllers, there are 14-way socket pads on the board. I have no info whether they enabled the jtag lock.

i found an eeprom 95640 with the vin number inside, i took a chance and swapped the eeproms

Indeed, this is great. I would have espected they use internal flash for this purpose.
Now I see

hopefully it works, i'll report back with results, seems to good to be true though,

Ok guys, I got an update, when I swapped the 95640 eeprom into the doner inverter the immo faults have gone but still have these faults that were on the original inverter, at this stage, I'm lost

Looks like it needs a position sensor relearn and the other recharge code is a bit weird, might have a resistor or relay fault for the precharge side of it maybe?

Agree, I think checking the precharge resistor is a good idea

Found the problem guys, it was the pre charge resistor blown to pieces, does anyone know where I can source one ? Cheers.

I do not have personal experiences with it, but norwegian scrappers are said to be a good source for cheap replacement parts.
In case you have more photos of the junction box, and a short description of how to find and open it, I would like to collect all these in my Ioniq documentation at https://github.com/uhi22/Ioniq28Investigations

Does this box have a separate part number, or is it part of the battery pack?

Hi uhe22, as far as I know the box is separate, Hyundai were looking for €900 for the box but when he opened it, he found the resistor, he said it was quite easy to access, at first he thought he would have to drop the axle to access it but it was not necessary, I will ask him to send me some pics for you, I found a resistor on eBay for a good price, he's going to purchase it today, I'm not sure if I'm allowed to post a link, I'm on the phone at the moment and I can't put the link into a text file, I want to thank you guys for the help and input, really appreciated, I'll get the photos for you as soon as possible, cheers guys, goodluck.
https://ebay.us/m/VrB4O4

Some pics for you uhi22

Have another issue, the immo fault has appeared again on the doner, perhaps I should have used write protection when writing the eeprom ?

Maybe, when doing toyota immo stuff I had to use write protection, each time after 1 start it would delete the data i had written and had to redo it again

Yes, I hope so Doig, tomorrow I will collect both board's again and check the data, strange that it just appeared again after he installed the new resistor, thanks for the reply, I'll update tomorrow, cheers.

For uhi22

For uhi22

For uhi22

al70 wrote: ↑Sat Nov 15, 2025 11:34 pmFor uhi22

Thanks, just had a look to the first pdf, it is related to the hybrid variants. The fully electric is different.

Some more pics of the Ioniq for you uhi22, the relay is good, the resistor is good. I've 380v at the input. Bms board looks ok so I'd say it's one of the + contactors, honestly don't know what to check now

Any chance to measure the control voltage on the coils of the contactors? Maybe a high voltage fuse blown in this box? Is it possible to draw a schematic of the HV pathes of this box and then to measure where the interruption is?

I'll pass that on uhi, we're almost there, something simple I think is preventing the start, I'll keep you posted, cheers, goodluck.

I just checked for HV at the terminals into the PRA. Too tricky to do meaningful testing with HV on it so I bailed, pulled fuse and dropped battery. I checked the three big fuses in the junction box and they were all good. I'll drop in a replacement PRA see how it goes and do an autopsy later

Right latest on the Ioniq, precharge resistor had blown again somewhere along the way. Measured capacitance at the Jc junction box and it was way out of range, disconnected ptc and it came a lot closer. Low resistance and ptc terminals so suspect ptc heater pulled down the precharge resistor

Maybe in place of the precharge resistor put two 230V 40W light bulbs in series so you see whether the precharge works.