P0A08 error code

Previous thread (with new subject title) on my 06 Prius losing steering and brakes while driving with multiple errors (red triangle, battery, etc.) while braking on steep down hill section of hwy 17 (mountain road). Took car to dealer but dealer could not find the root cause.

Print out from dealer:
131297 found code P0A08. dc/dc converter status circuit. checked aux battery-passed load test. Check cable connection from auxiliary battery terminal - cables connections are secure. Checked inverter water pump coolant level and operation-pump is working.

So I had them replace the 12V aux battery. So far no relapse of this problem with one day driving with the new 12V aux battery. I am not convinced that this is the root cause.

Galaxee and Patrick Wong had previous threads something about DC/DC converters overheating when the inverter pumps failed - and perhaps that is closer to the root cause of the issue my 06 Prius is having.

Thoughts?

 

I checked the hose between the driver side headlamp and the fuse box and noted some slight vibration when I put my finger on it - so I am guessing (if that's the inverter coolant pump hose) its working.

Which coolant reservoir is the inverter coolant - the yellow fluid reservoir?
Thanks