I just checked all voltages from inside the MCM (was very careful to not make any shorts) and they are all good. I guess all options are exhausted now, so I will order new MCM.

 

I got the MCM replacement today, installed it in the car and it's working! Went to do the vehicle inspection since it expired in the meantime and it passed without problems. Thank you very much for all your tips and advice, wouldn't be able to solve it without your help!

However, when I was driving back home, the engine light got on again and I checked with the scanner and got P0404. I'm not sure, if this is realted to what I was doing in the last two months at all. I just deleted the code for now and will see, if it returns sometime.


Two questions poped up in my head now:
a) Is IMA firmware installed on the MCM or somewhere else? I mean the software that received that update which then uses the battery in a more conservative way.
b) How often do you suggest that I balance the IMA battery and should I do the full 3 cycles with deep discharging (like I did the last time) every time? I would like to keep the battery in the best shape possible.

 

P0404 is "EGR valve insufficient lift detected" - if it clears and stays away for long periods, I wouldn't worry about it. There are some electrical connector checks, but if the light stays out most of the time, it's probably just a failing EGR valve.

a) MCM. The software to which you're referring is only applicable to 2006+ HCH. There was no "conservative" update to the 03-05. The "update" to the 03-05 was to eliminate the PTC circuit.
b) overnight charge (8-12 hr) only 2-4 times per year. ONE of those charges should include the prior full charge criteria, and ONE discharge to 96V once per year followed by another topping charge.