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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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Is this in the car (and what car) or on the bench?
Again, is this in a car or on a bench?

If in a car, which one?
So, it's in a Volt, then?

Take it to the dealer.
This is clearly something a dealer won't touch, and you appear to me to be weaseling the location of the IMD vs saying whether this is your own contraption (I image processed your scrap piece of paper, lol):
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And being your own contraption, the Volt pack is not happy with it, so you're looking for a defeat. If that's the case, you should spell out what you are doing so you can get ideas from people here of how to remedy the fault.
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That is not chassis ground. That's the board ground. Chassis ground would be connected through the missing device above the one your highlighted red run is showing.
Those resistors are locally grounded on the board - "ground" is a common return for the circuits on that board.

The four caps KB circled are the only connection to chassis on that board - the schematic is wrong.
Caps are easy to R&R and, technically, you can probably run the car without them...
You cannot get megs of isolation with a 51k resistor connecting to a board worth of circuitry.

I'm not buying that resistor via goes to chassis ground - did you verify that via connection by eye or with a meter?
One thought - did you replace any coolant lines or do any work on it at all?
Yeah - you better look. There could be something else making that connection.
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?
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