2015 Prius V electronic key lost transmission with the vehicle

Get a multi-meter and check the voltage on the battery.

Do you have another functioning key? Try it out for function check.

 

(1) Try using the dead-fob-battery method of opening and starting the car. Use mechanical key (in fob on keyring loop) to open the door. To start engine, press brake to wake up the electronics, hold fob to the start button so that the very-short-range RFID detection works, then start car. If this works, then a dead key fob battery is the most likely explanation. (the multi-meter mentioned above is better, but not everyone has it available.)

(2) Did someone turn off the Smart Key System detection before the trip? Check, and turn it back on if necessary. This is done from the vehicle setup menu on the big screen of my Liftback, but your 'v' would have different menus.

 

Most likely that the 12 V battery has gone dead in the car.
Have that tested first.

If you do NOT have a second remote key, GET one soon.
If you lose both......or both go bad......it is a VERY expensive thing to fix.

 

welcome to PriusChat!

 

You might have to pair it again. I think you have to hold it on the push start button. There is a tutorial I think I'm the manual.