Dreaded P-Lock error

So it's my turn to solve this P-Lock mystery on the 370,000 mile 2008 Prius.

Last week about to go home for lunch and the car brake peddle sunk an 1" or 2 and the lights went dim on the dash. Then completely dead - no 12v power anywhere - not even door locks.

Get AAA out to jump start and it fires right up and displays the P-lock error.
The tech checks the 12v battery and seems to be holding enough volts for him to give it a pass as the problem.

While the car is running (very cold day) I decide to run it home and park it. I get home and turn off nd back on and starts no problem. Brakes seem to work fine and the HV battery remained on 6 bars. The roads were icy so I took extreme care fearing the might be a problem with the breaks or the car stalling. It's only a mike to home so was relived to make it and not be a frozen victim broken down again.

So wife unlocks the car to put the code reader in the car for me and after work I brave the cold to only find the car is completely dead with the drivers door unlocked. So no codes.

Seems different to others that still have power to the car in some form.
The 12v was not new but also less than 2 years old and tested fine on the techs load tester.

So something is cutting all power to the whole car. I can try and jump start again to see if I can get some codes to work with.

 

OK the car has sat berried under snow for a while. The battery was checked by the AAA tow company and said not the problem.

I was driving the car most days and making sure it got warmed up after the milky oil last winter.

I'm leaning to a bad earth or the voltage not getting to where it needs to for the car to run.
It is strange for it to fire up on a jump start and then drop dead for the next start.

 

So when you first start the car it's on the 12v and then goes over the the HV system yes?
If that's the case then the 12v system is redundant once up and running.

I have no issue with buying a new battery - but hate to do that only to get stuck the next start.
So once the snow/ice melts a little more I can get to the car. The ice is packed up to the door so impossible to work on it just yet.

 

It will jump start and run, Stop turn off and it is 100% dead - no door locks nothing

 

Yep - cant lock the car. completely dead.

 

less than 2 years and was load tested by aaa

 

Update:
So the snow and ice has melted some and I could get to the engine bay to test a jump start. Got the the same brake peddle issue and no start this time - still totally dead. Time to pull the 12V battery and get it tested. Turns out we have 1.4 volts and a very dead battery.

Buy a new battery and install it. Had to jump the power again to unlock the tailgate lol - it was a fighter all the way.

Car starts on 2 cylinders after not running for 3 months. Then 3 and finally after what seemed way too long, all 4 and smoothed out some.
It logged no codes at all throughout this whole dead time.

But I cant move the car as the ice has it still trapped in place. I can move it a little back n forth.
Looks like hot water might help or wait another month for the warmer days to melt the ice.