Hey Dolamo. Unlike the great many other functionality of your Yaris or any other model, which can be pretty hard to troubleshoot, wiper are not so. Follow the below steps to try and isolate the cause of your issue. Otherwise, the issue can either be electronic or mechanical.
- Check to make sure that any of the wiper blades is not stuck - yes they do get stuck unfortunately
- Engage the wipers and listen to hear if the is any sound of the wipe motor running
- If there is, then it must most likely be a loose linkage - this is quite common
- If you cannot hear any sound of a running motor, then is may be a bad fuse
- Locate your manual - and head to 'Fuses and relays or circuit breakers' - there in lookup the numbering of your front wipers fuse number and check to see if it has not burnt and replace it if it is burnt
- But if the front wiper fuses checks OK, then you may be having a burnt wiper motor due for replacement.
Note: If you are still under warranty, (be it limited or extended), take you a trip to the dealer and safe you from much :)