Heated seats stopped working - Prius v (lowercase v for the Prius v wagon)

welcome! very odd. when odd things happen, check the 12 volt!

 

Based on the attached schematic, if you have LEDs ON at your switch, you should have power to the seat heaters. Otherwise look at the 10 amp fuses and the switch itself. If no LEDs, check the fuses with a voltmeter on both sides to ground and then try to check the switch itself for power. A bad ground in the circuit could cause the issue. If you are not handy with voltmeters an audio tech installer (short of paying the dealer) who is used to working behind the instrument panel might be the answer.

The second attachment shows the seat heaters are part of the upper and lower seat covers/cushions and are not available separately . In this illustration they are sold with the covers as 71072S bottom 71074S top but many varieties based on interior trims. Actual part numbers are different based on the trim and heat / no heat.

Checking for power that switches on and off at some connector under the seat would be my next step assuming fuses and LEDs are good. Going to Toyota TIS and finding specific instructions ($15 for two days) would be a good plan. If you found seat heater switchable power under the seat and still no heat, probably the heater themselves, which look expensive at $200 or more each. I would try to ohm out the heaters but there is likely to be some kind of safety control with them to avoid overheating, so ohming might not work. You could pull the covers and try to find the heater. Going to the dealer parts counter with your VIN will get you the exact part numbers and pricing and "maybe" a look at the parts if they have them in stock.