Where do go from here, think I have a dead HV battery?

To make a long story short:
My daughter's 04 Prius won't start, and shows the 5 squares on the speedometer, then shuts off. 12v battery appears to be OK, MFD lights up in acc mode, but code reader won't connect to show codes.

Problem is most likely self-induced, little bit of history:
I removed the inverter reservoir to change a broken AC hose, apparently didn't get the O ring installed correctly, started leaking shortly afterwards. Daughter took the car to Houston anyways, and I drove down the next weekend and installed a new O ring which stopped the leak. However, the red triangle of death showed up next day after I had left. (maybe I didn't get all of the air bled out of the inverter coolant system, btw, the inverter coolant pump was changed last year) Autozone checked the codes, said it was just a bad O2 sensor (this was an old code), so she kept driving it. Car has now shut of completely, assuming HV battery is dead. I drove to Houston Sunday and brought the car back on a trailer, (it's really hard to load it on a car trailer when you can't put it into neutral)

Where do I go from here?
1. Is it normal to be unable to connect with a code reader if the HV batter is dead?
2. Can I charge the HV battery in the car, or do I need to remove and disassemble it to charge each cell individually?
3. Am I missing something simple, what else can I check

 

Thanks for the advice, really appreciate it. I don't have Techstream, but I've used my bi-directional Autel MD802 to pull and clear codes from this car many times in the past, so I don't think that's the issue.

Is there a write up somewhere on how to charge the battery in the car? I'm not opposed to pulling the battery, but having done it twice already, I don't want to if I don't have to.

About three years ago, the odometer stopped at 299,999, so I'm guessing around 350k. But that's probably not too relevant, since I've changed the engine/transmission once and HV battery twice.

 

Thanks for the response, I may have been somewhat unclear in my original post. The MFD (in the middle of the dash) works fine in acc mode (start button without touching the brake) but if you step on the brake and try to start the car, the speedometer/gear indicator flashes on very briefly, then displays 5 squares, while the MFD never lights up. Other posts I've read say that's classic inverter coolant pump symptoms. Since I just re-installed the inverter cooler reservoir, I'm looking in that direction.
The 12V battery shows 13.6 Volts at the underhood jump point, but I haven't figured out how to check the HV battery voltage yet.

What's the easiest way to check HV battery voltage? I know I could remove the inverter cover, and check the voltage at the DC input to the inverter, but I'd really like to check it as close to the HV battery as possible.

 

Thanks for the sage advice, sounds like I’m barking up the wrong tree worrying about the HV battery at this point. I’ll unplug the inverter water pump tonight and see what happens. I’ll also test the battery to see if it’s ok.

 

Thanks for the advice, it was absolutely correct. Unplugged the ICWP, no change. Found AM2 fuse was blown, replaced it and things started working again. Plugged in the ICWP and the fuse didn’t blow, but didn’t take long to figure out the cause of the problem. After 3-4 minutes of looking around, smoke started pouring out of the ICWP. I’m thinking that maybe the missing coolant reservoir o ring got sucked into the ICWP and locked it up. Still shows red triangle and all warning lights, so I’ll get my code reader and keep looking around for other issues. You just saved me untold hours of wild goose chasing with your advice.

 

ICWP appears dead/locked up, got a new one coming. Still have red triangle, abs, check engine, vsc, and red car exclamation in the mfd, so I assume there are still some issues remaining.