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Chevy volt BECM IMD (insulation monitoring device) and battery insulation informations

3145 Views 50 Replies 5 Participants Last post by  remy_martian

I would like to know if someone already deep studied or reverse engineered the insulation monitoring device integrated on the BECM module of the chevy volt Gen1 ?
I know that it's not the most appropriated forum category but I know that's is probably where I can potentially find this kind of informations.
At the same time I'm also looking for someone that already measured insulation values of a complete chevy volt without and with official GM coolant inside with a megohmeter ?

I'm currently fighting with capricious Chevy volt on which I've tested insulation of all the HV parts independently, with very good values on all of them including the battery pack, but the car's IMD still measuring a low insulation value.

So I started to reverse engineer the IMD to find any problem on it and I'm looking for references values of battery/modules insulation.
For the moment I get >2000MOhms @500Vdc on the total battery pack without coolant and >30MOhms when it's full of official GM coolant. I can't imagine that this value is considered too low by the IMD...

So i'm interrested by any reliable informations on this topic.



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Any new findings? Have had Opel Ampera with low measured isolation value (250k) while charging. Replaced battery coolant heater, new onboard charger, checked all HV cables and HV battery. Nothing helped. By doing various experiments I noticed that isolation value did not drop if charging with disconnected mains ground.
Does that mean "yes", or is it sarcasm?
YES. When not charging BECM reports 3000k which is max value. And if charging with mains ground disconnected it stays the same 3000k. But as soon the mains ground is connected it drops to ~250k.
Sounds like you may need a new charger.

It's the only component, other than the charge port and cables, that knows about chassis ground.

Maybe disconnect the charge port cables at the charger and test the isolation to verify a charger fault?
Charger has already been installed brand new
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