My son drove his Prius into 2+ feet of standing water

My son’s a new driver, just got his G licence, and loves his Prius. He’s blaming his nav or failing to respond correctly for driving through deep standing water getting off the Highway, vs pulling onto the shoulder. Be that as it may, he drove through this deep water (top of hood) that, after him, stranded a Ford F-150 and several other cars. At least he made it through the water bog!

He managed to drive another 1.25KM, almost home, and “the car started shutting down in stages”, first the stereo, then the dash, then the whole car shut down.

He managed to park it safely and called me at 11:30pm for help. The car seemed dead (12V) so we used a jumper pack and got it to try and start many times. Sounded like a really rough, misfiring rattling (heat shields) mess. We boosted from under the hood, (fuse box terminal) and at back of car.

We took out the air filter and it was (really) water-logged. :-/

No luck so we flatbedded it home (only 1KM!) and it sat in the driveway at -12 degrees Celsius 10.4 F and frozen. We finally installed the new AGM battery we bought 2 years ago, after fully charging it over night.

Got a Green Ready Light (!) and was hopefull but one clunk sound (to me it seemed frozen or seized and then flashing green ready light and nothing. The flashing green ready has been the common theme here!

Pushed car into garage with space heaters and model y set to 21 and “camp mode” and got temps up to 10 degrees or 50 F.

Tried to start again after 26 hours, and got a rattlingly quick misfire then flashing ready light.

Pulled the plugs before the start event thinking we’d blow the water out of cylinders but no such luck.

Drained the oil and replaced with heated oil at 113 F thinking it couldn’t hurt to try but it didn’t help. There was a foamy film on the drained oil, but not a lot.

Marked crankshaft pulley with sharpie, put a 19mm socket on an 18” breaker bar, and couldnt’t turn over the crankshaft even with the plugs out. Can the MG1 jamb the engine trying to start? Maybe engine is still frozen? I don’t know what to do other than give it more time to thaw out?

other than the non-ready light, lots of clicking from HV battery area.

The car is in excellent shape and only has 51k miles on it. We both really like the car and are afraid Toyota will write off the car and write us a cheque which we don’t want. He said he’d like to drive it another 10 years, and I don’t blame him. This little car has something about it we love, we don’t want to give up on it, can’t afford to replace it, but can put money into a repair if needed, but we’re just puzzled as to what’s going on.

Lastly we tried Maintenance Mode. Tried to start for maybe .25 second and that was that. Nothing.

Would really appreciate some real world feedback from anyone that has been through this and not just ChatGTP because that hasn’t helped us much.

Thanks so much!

P.S. I hope I’m in the right forum, sorry if I missed that