Prius completely lost engine power *after* mountain pass

Of all the loads you mentioned there, only the A/C is very significant. I guess the gen 2 halogen headlights would still account for 110 watts or so. Maybe the radio can use a hundred or so if you blast it at ear-splitting levels. (I haven't looked up those specs for the stock amp.)

The A/C can add 2.5 kW or so, but only if you set the temp to make sure it's running flat out (it's variable speed). So yeah, that (more or less by itself) may increase the amount of power you can dump by another 25% or so of what the engine can do, but I'd think that's about it.

 

The cabin fan at full blast is somewhere in the vicinity of 15A. Round it to 200W. Rear window defrosters are that or more. It isn't 2.5kW, but it moves the needle towards 3kW, and with everything going at once, probably past it.

Hmm, the conversion efficiency from the regenerative braking isn't 100%. I have to think on if that makes these electrical loads more braking or less braking. Feels like a trick question.

 

I guess the ultimate limit for braking through the 12V system is how much current the inverter can supply at that voltage. 100A is the number that sticks in my head, and maybe 20A of that is in use by the rest of the car. So 80A x 14V is 1120 Watts, and no matter what 12V electrical devices are turned on, it can't go beyond that. The A/C runs at a higher voltage on a different part of the inverter, so it can be 2.5 kW, independently.

 

No reason you can't count the maybe 20A used by the rest of the car as load, too. So you can think of a max 1400 W being dissipated in the 12-volt system. (Also, the conversion inefficiencies in the inverter and converter can be counted; they're getting rid of some extra power as heat.)

 

The Tioga pass is scary enough at just under an 8% grade. I think it's the "rock wall on one side, cliff on the other with no guardrail" sections that give it that extra "no errors allowed here" factor. On the other end of 120 there is "New Priest Grade" which is the longer and windier alternative to "Old Priest Grade". The latter is still in use and has sections which are said to be at a 17% grade (some say 20%, in any case steep), whereas the former is only a 4% grade. 120 is not a road you want to be on in a car that is mechanically suspect.

 

Something disconnected then reconnected after cooling down.
1. When you jumped on the accelerator peddle, did the engine revved or nothing.
2. On the Gen2, do they have an ATF cooler?
3. When was the last time the ATF was changed? Hitting steep mountain passes every quarter is severe duty, besides 200K+ miles it's due for a change.

 

The transaxle containing MG1 and MG2 is cooled by the same loop as the inverter. It doesn't have the same sort of engaging/disengaging gears as a normal automatic though. If that coolant was too hot the same symptoms as an inverter pump failure would appear. The described failure does not match that, notably the absence of the big red triangle and corresponding codes.

Toyota does not specify a changing interval for the transaxle fluid. It isn't going to gum up the works like on a regular automatic if it goes off, but if it becomes acidic it could cause problems with the wiring, including in the electric motors. If it has not been changed in 200K miles it would certainly make sense to do so. Also, unlike a in an old conventional transmission, changing it will not cause problems, at least as long as the right fluid is put back in and no contaminants are dropped in with it.

 

from maybe the inverter overheated so the car shut down off or something weird?

 

The car puts up the red triangle of death and lots of other warning lights come on when the inverter overheats. The OP reported no lights.

 

That reddit had an instance of it not starting without any lights...except the door light, so I wondered if maybe related or might have interesting ideas Anybody know of any concept of anti-overheat self resetting fuse I wonder....