Red Triangle. Unsure if Battery ECU or other issue?

Hello. First time posting please forgive me. I've not had my prius (2007) long but trying my best at self maintenance and appreciating reading this forum.

I've got a red triangle of death and on plugging in the laptop have the following errors codes:
- P0A84 Hybrid Battery Pack Cooling Fan 1 Control Circuit Low
- P3000-123 Battery Control System
I was really hoping its not an ECU or HV issue so I was hoping it was possible the fan problem was also responsible for the P3000 code. I have noticed the battery level displayed when driving has been a bit erratic, but I'm not sure if I'm just being paranoid.

I've checked everything I can with the HV fan/blower, it runs fine when taken out of the car. No blown fuses and 12V is coming in on relay input. Swapped relay. Good connections between all wires on fan, relay, motor controller & ECU. No identifiable corrosion or damage on ECU pins. I tried putting in a new AGM 12V battery. And I even tried plugging in a spare motor controller.
On clearing codes and running battery fan test the fan doesn't run and the same errors come back.

Is there anything else I'm missing? Or am I barking up the wrong tree and I need to replace the battery ECU? Is there a test I can do myself to determine if it is a battery or ECU issue causing the P3000?

Thanks for any thoughts or suggestions.

 

Got about 95k on the clock, and due to pandemic only a few of those are actually mine.

The block voltages are all about 16.6 V in techstream <0.2V difference across them.

The only sub codes showing is "123" under P3000 which the service manual directs to "REPLACE BATTERY ECU ASSEMBLY".
Following the P0A84 instructions in the repair manual there doesn't seem to be anything else I missed and it finishes with the final step "REPLACE BATTERY ECU". So its seems reasonably clear what I have to do.

I am struggling to find which bits constitute the assembly and the replacement procedure. I think I read elsewhere the battery ECU can be replaced without any re-programming etc but obviously want to be sure before I start.

 

Thanks for the suggestions.
I had checked the fuses with my multimeter, no problems (I got carried away and checked them all).

I have consulted the manual and gone through the procedures, though I could perhaps stand to go back through them again this weekend and be a bit more meticulous.
Straight off the bat there were issues. There was no voltage reaching the battery circuit from the battery fan relay (B14) when running a fan test. I confirmed this both manually with an external meter and with the battery ECU readout from the reading on VM. The relay itself seemed fine, though it's damn fiddly to test so I swapped it out to be sure.
I checked all the connections through to FCTL1 on the battery ECU which drives the relay were good, so it seemed like the issue was the ECU not activating the circuit.
This is where I went off script a bit and shorted the relay connector to see it was just a problem with FCTL1.
Now VM read 12V but the blower motor still didn't run when running a fan test.
This is the point where backprobing and looking at the signal onto the motor controller would have been a good idea, but I didnt, I'll get back to you on this.
All the connections to the motor controller checked out, so I swapped in a spare motor controller to no avail.
As a last (and unrecommend) resort I removed the motor controller and shorted VM to GND on the connector, which should create a simple 12V circuit for the blower fan, removing ECU and motor controller from the equation, but the fan still did not run.
At this point I checked again that I wasn't mad and the fan does indeed run fine when taken out the car, it runs smoothly at 12V and draws about 3A.

So I was stumped. The wiring and connectors were all solid connections where they should be, there seems to be some issue with the relay/FCTL1 but then also I can't get the fan to run when bypassing that issue.