gas engine won't crank

Most likely you have moisture/water in some of the HV cable connectors or AC compressor. The HV system is supposed to be completely isolated from the car body(chassis ground). Moisture in connectors tends to cause problems, either between the HV system and chassis, or between the two HV cables. The best thing you can do is find someone with techstream to go on line with your car and see what the shortwave value is. It will be a voltage measurement from 5v to 0v. 5v is the best insulation resistance. 0v is the worst. It would at least give you somewhere to start.

You can always try unplugging the AC compressor power cable from the passenger side front corner of the inverter. If the AC compressor is the problem, it should remove the AC motor from the circuit. See if it makes enough difference to let he car go ready.

Also, as a reminder, Prius and flooded road just don't belong in the same sentence..........

 

Look for water in the orange high voltage cabling to the transaxle or the AC compressor.

 

That code generally means the safety interlock plug was removed at some point and not re-installed correctly.

Usually the third step of ensuring the handle is pushed downward until it clicks firmly into the locked position is not done correctly. You should check this before moving on to more involved diagnosis.

 

Pretty unusual for that code to show up while driving. Maybe the fuse inside the safety disconnect popped during the "at one point the motor did crank once and that was it.." episode.
If the fuse is good, it may be a wiring issue for the interlock circuit.

How high was the water? Did anything get inside the car?