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

3076 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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Ok, I must be dumb, but I have issues with just half the pack voltage being grounded through anything. How and where are you measuring this ?

Is your coolant conductive? Premix should be DI or distilled.
On mine that resistor is tied to chassis however I do not know whether mine is functional since (oh horrors) I don't use the BMS

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Mine is an October 2011

@kennybobby: insulation degrading? Perhaps to the point of leakage, but that typically isn't an insulation thing, it's a connection corrosion cause. I cant see where an insulation could cause a leak without a big failure immediately later.
Edit: everything this stuff is attached to is generally plastic
In that case, disconnect the IMD and remeasure isolation. While being a royal pain, it will determine whether or not the IMD is faulty. Otoh, other than my unit, where do you get a new one? I am impressed you are pulling this pack apart and re assembling.
On my pack everything was clipped to a plastic housing then has an isolation cover of plastic so in the parlance double isolated. Only the harnesses interconnect to anything grounded to chassis . A coolant leak, defective unit, the internal heater, or a frayed harness are pretty much your only choices for high voltage leaks. The way it's built exactly 1/2 battery voltage isn't easily done because there wasn't an external connection at that point. But hey, it's been 8 years since I got mine, so maybe I forgot something
Afaik, nothing HV is tied to chassis directly. I dont remember grounding straps, but I do recall pulling the main cover and checking against the metal backplate and getting no continuity anywhere on metal things sticking out. Wasnt any info online except for eggbert tearing his apart.

Disconnected, I found it to be an expensive useless brick.
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