12 Volt Battery - what does cutting power from it do?

[TrevTremaine]

I'm trying to understand something about how power flows through Teslas: In the accident I recently had, the firefighters cut the 12V battery cable as per instructions. Although power to the console and Instrument Panel was gone, we were still able to activate the doors and the trunk. Some hours later I was still able to receive telemetry from the car (location and main battery state) from what I recall, but was unable to communicate with it by morning.

So, what does cutting the 12V battery cable do? Seems to me that the car is essentially still powered, whether it's "ancillary" functions or more, I've got no clue.

 

[f-stop]

I don't have a definitive answer, but you might some info in the emergency responders guide, here: First Responders | Tesla

e.g. from the 2015 dual motor guide on that page, it says:
"FIRST RESPONDER CUT LOOP - FRONT TRUNK
The front trunk first responder cut loop consists of low voltage wires. Cutting this loop shuts down the high voltage system and disables the SRS and airbag components."

so of course cutting the loop disables the contactors and the HV system. It specifically mentions disabling the airbag system, but doesn't mention the other systems powered by 12V which are listed a paragraph or so earlier in the guide, so I wonder if cutting the first responder loop perhaps leaves some 12V systems powered? (I'm not sure)

btw, the inside front door handles are mechanical, so using those will open the front doors whether there's 12V power or not. However the rear trunk or rear passenger doors will not open via their normal release handles without power.

 

[mblakele]

I'm not sure exactly what cutting the first responder loop does either. But I'd avoid trying to open the doors if the 12V is disconnected. You risk breaking the window.

 

[TrevTremaine]

I'm not sure exactly what cutting the first responder loop does either. But I'd avoid trying to open the doors if the 12V is disconnected. You risk breaking the window.

The door handles didn't present on the accident side (most likely because the wiring through that side was ripped off), but I did manage to get access through the driver's side as the power was still available without issue - the doors, trunk and windows still were powered when collecting personal belongings the following day. I take it that telemetry might have a separate battery backup that would last for about a day or so, if indeed it's also powered via the 12V - any ideas?

What's unclear is coincidentally the issue over app access for a few days around the time of my accident.

Well, in my case it's kind of irrelevant (the front passenger door was completely ripped off and embedded in the hood of the other car) - the car was pretty much destroyed. Thankfully, no injuries beyond scrapes and bruises. Still waiting to hear back from insurance about the course of action.

Tesla Accident

• TrevTremaine
• Mar 3, 2017
• 4

T-boned by an SUV coming out of a parking spot.