Can anyone explain this behavior?

Did you encounter the front door handle area that locks/unlocks all the doors when washing with your hand, and key fob in your pocket?
Put the key fob in the house and try washing it again, in a few days when it needs another washing.

 

Is -25 deg C approaching 10 deg F, at which point the car climate control system is said to stop heating the car ?

 

Water from the hose will trip the lock/unlock trigger on the door handles when the fob is in my pocket while washing the Subaru.

 

Happens with my 2010 at the car wash routinely. Owners' manual mentions it:

 

in some cases, 2 m may not be enough

 

the heat pump is inefficient, but the engine produces plenty of waste heat

 

I always disable the fob when washing my car. Hold down the lock button while pressing the unlock button twice. The fob light will blink twice. Pressing any button once it is disabled will re-enable the fob. I found this info in my 2017 Prius manual as well as in my 2022 Venza manual.

 

Hmm, doesn't seem to be a thing with a gen 3 fob. Too bad, that would be convenient.

 

question

 

Is that waste heat used by the heat pump to heat the car ?

 

Not in the Prius. It takes heat from outside air, which is more efficient than using an electric resistance heater. Heat from the engine goes directly to the vents through the heater core.

Some BEVs have their heat pumps gather heat from their motor/inverter and/or batteries.

 

Not sure what the question is, but as Trollbait said, there is both an electric heat pump and a heater radiator core in the Gen 4 and Gen 5 PHEVs. They are independent. Even with the A/C and fan off, you will get warm air from the vents if the engine is hot and the car is being driven fast as the fresh air from the outside goes through the heater core.

 

I did not now that there is a heater core in a US 2024 PP XSE model.

 

Your body or something else is rubbing on the lock button on the door handle.

 

There is one in the Gen 4 PHEV. Since Gen 4 and Gen 5 are practically identical cars, I am sure there is one in the Gen 5 PHEV as well.

 

This is the coolant system with the heater core in the Gen 4 PHEV. The heater core is described as “straight-flow aluminum II (SFA-II).”