I have been led to believe that's all it takes... I had my first experience with a Y a couple weeks ago and it was incredibly frustrating (I dropped a socket ) and ended in defeat. I simply couldn't figure out how to disable power in the Y to reboot it.Thank you for this great thread, FalconFour! My case is the more simple one where I need to swap my ECU (1537264-80-B) with the CCS-enabled one (1537264-00-B). I ordered the part from my local SC today and should have it next week. In preparation, I watched a video on how to access the 12v battery in the Y and part of the video showed the presenter disconnecting the First Responder loop:. Would doing that have the same effect as unplugging the connector under the rear seats?
I also found the Y seems significantly more complicated to access the ECU on... the trunk layout is totally different. No idea how to get started there, but if you do find it, it may be a bit OT in this thread (for the 3) at *this* moment, but the overlap means this thread could evolve into instructions for both the 3 and the Y (which is generally already Gen4, but some with the stripped issue as you have).
Anyway, at least in the 3, if you unplug that connector under the rear seats, without unplugging the 12v battery, it disables the PCS but the car stays awake using its 12v battery... in kind of a "waking up in middle of surgery" moment. It's not terribly happy with that. Not sure exactly how the first responder loop works, but if it's really that simple, it could work well. Please do let me know what you find - if it actually kills power to the whole car or not
If your MCU screen goes dark, that's all it needs.