how do i set the interior lights to go on automatically when the door opens?
Check dimmer switch. On some vehicles when dash lights are dimmed to their lowest position the interior lights will not come on when doors are opened.
If that interior light is still not fixed perhaps it could be a computer module problem, btw you should still be covered by Toyota warrenty have them check it out for free.
This seems silly, but it took me 30 min to figure out that there are 2 switches that control the interior lights coming on when the door is open. The obvious one is in the complete center of the car (sort of over the driver's right shoulder - and this one should be set to "door" But it still won't work UNLESS the front-top light switch (sort of above the rear- view mirror) is also set to DOOR.
Looking for a Used Prius in your area?
CarGurus has 22,585 nationwide Prius listings starting at $1,250.
Search Toyota Prius Questions
Toyota Prius Experts