I cleaned the corrosion out. the fan is still blowing- so its working. its blowing a bit hard- and consistently from just a few seconds after I start the car. I thought maybe the inverter coolant pump needs replacing- but my home mechanic wont mess with it and Toyota quoted me $4000???!?? not sure if they misread something... and the Toyota phone person also told me they "stand by the maintenance codes word" and insist its my hybrid battery. edit: I also sealed up my hatch to prevent any more water from getting in.
it could also be corrosion inside the battery case and connectors. shop around some more dealers, and look for a hybrid mech. the inverter pump is an easy job.
Im in the midst of this right now myself.. Just put in my 3rd 12v battery.. After the original died, bought a new 84 month from the dealer(march/2016 $313.00).. that one went out yesterday/today.. Took it out of car and to dealer this morn.. With the warranty, got a new of the same for $145ish... Installed it, car started right up.. red triangle.. but my code reader would give any codes other than those 'you just disconnected the battery now you have to drive it around before you can smog it warnings'.. Came here looking for answers.. Found some.. Hastily may have posted my problem in the Gen I forums.. Went back and tested new battery and it was strong.. Started car.. No red triangle.. In fact, I have no dash lights at all.. Right now I'm chalking it up to that BS these Gen II's do sometimes.. With the no dash lights or won't shut off without holding the button Gonna keep trying trying the car for dash lights etc.. When I connected the battery installing it, the whole car turned on.. radio too.. That seemed weird.. Don't know if the engine part came on too. I think it was just the 1st aux 'on' mode..
Whenever I disconnect a 12v battery on a Gen 2 prius, if I don't use a battery saver on the front jump terminal, the first time you press the power button(with foot on brake pedal), you'll have a ton of warning lights. Press the button again and all will clear, unless you have a real problem. Does it every time. That's just the nature of the beast, and I'm pretty sure Toyo mentions it in one of their manuals.
Yea, Mine's all good. A couple starts, a trip around the block and another unplug/replug of those positive battery wires/clips.. Back to normal.