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Discussion Starter · #1 ·
Grid charger just started turning on all dash as if the key on, beeps for a moment as if the ign was just switched on. This happens as soon as it's plugged in and enables the IMA fan. Doesn't matter if the grid charger's switch is on. Everything else is fine. I really don't think I just overlooked this before. Any ideas? If it was a stuck relay, I'd thing it would do this without the grid charger.
 

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It does happen occasionally on some of the cars. It is the grid charger 12v back feeding through one of the fan relays. The IMA fan relays are on the IMA compartment.
The first one of these I saw years ago, we installed a diode on the fan power wire to stop the problem.
Scott
 

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^ Interesting, I've never heard of this problem before now.
 

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Where do the grid charger fan wires connect? I'm looking at the wiring diagram and I don't see how the dash would power up, unless the grid charger grounds to both the fan and the chassis. The negative side of the fan only connects to the relays, which should be off. The battery fan relays are forward of the battery on/off switch. You could try unplugging them. If that solves the problem, it's either stuck relay(s) or the BCM turning them on.
 

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Discussion Starter · #5 ·
It does happen occasionally on some of the cars. It is the grid charger 12v back feeding through one of the fan relays. The IMA fan relays are on the IMA compartment.
The first one of these I saw years ago, we installed a diode on the fan power wire to stop the problem.
Scott
What's the minimum wattage rating for that?
 

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The diode only needs to handle 500 mA at most. Assuming a 0.7 volt drop, that's 350 mW.

I've seen this behavior manifest itself several different ways over the years. One way it can happen is that the BATTFANH/L line gets enough voltage on it for the BCM to slightly power on, which immediately causes it to bias the BATTSCI serial bus. If the bias rises to more than ~2 volts, then the MCM can turn the relays on (drawing power thru MCM pin VBU).
 

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Discussion Starter · #7 ·
The diode only needs to handle 500 mA at most. Assuming a 0.7 volt drop, that's 350 mW.

I've seen this behavior manifest itself several different ways over the years. One way it can happen is that the BATTFANH/L line gets enough voltage on it for the BCM to slightly power on, which immediately causes it to bias the BATTSCI serial bus. If the bias rises to more than ~2 volts, then the MCM can turn the relays on (drawing power thru MCM pin VBU).
I've figured out that it only happens when a 400W block heater is plugged into the same circuit.
 

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My first guess then would be that you have a floating neutral in your house wiring.
 
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