I am very new to working on the Prius and very new to this forum so please be gentle. Is it almost a definite that these codes are caused by bank 12? I did find some corrosion at the cooling fan connector and cleaned it up as good as I could with no i.provement. All connections at the hybrid battery and hybrid ECU are very clean. I have not removed the top of it to inspect yet.
It is very obvious that one of the two modules that make up block #12 is bad. You need to replace that module OR replace the complete battery pack, whichever you decide to do.
This repair is defined by your budget... You can watch Youtube videos on how to simply replace the bad module for $35 via this guy: Hybrid Car Battery Distributor | Contact Us | 2nd Life Battery and sometimes people get lucky with no issues for a year... Or you could spend more money on gear to charge and discharge all 28 modules several times to recondition them, which will help you find other soon to be bad modules and if you do a really good job it will last up to 3 years. Or you can buy brand new OEM pack and install it yourself, or buy a Lithium upgrade pack via my affiliate link Toyota hybrid battery upgrade pack - NexPower Energy and get unlimited tech support from me.
