Any guesses on the likely cause of wiper failure...front only, passenger side. I don't have the car here but my guess would be motor failure.
i would think the motor drives both sides. maybe the splines are worn? or could there be a lock mechanism that has come undone?
If the drivers side works, it's not the motor. Something in the linkage. Or maybe the nut was/is loose. It's easy to take the top part of the housing off to look inside.
My money is with Bisco, but maybe its just the wiper arm nut that's become loose. You will probably get answers from a visual inspection when you get the car back.
Mrs. Bisco has placed her bet there. I think it's been for a significant period of time too. Certain traits must be redeeming.
One motor drives both wiper arms through a transmission linkage assembly. The "usual" failure point is the splined union between the driving shaft coming from the transmission and the root of the wiper arm itself. The locknut can come off, and the arm pops free. With any luck, there is still enough meat on the splines on yours so that you can re-seat it, and lock it back down with a new nut. If not, you'll probably need to replace the wiper transmission assembly. Usually cheapest to do with a junkyard part.
I sometimes need to remind my friends that I'm not totally useless. They can always use me as a bad example. Perhaps Mrs. B. has found that to be true with her hubby. Edit to add: Almost forgot the original question. I would agree that it's either a loose nut (not related to my previous paragraph) or the splines. Or even bad splines AND a loose nut.
if you like your money in a stock market that is probably gonna implode at some point, and cd's that probably won't be worth the paper they're printed on, this is the place to come.
Not sure if this feature is on the Prius, but I bet it is. Wipers have a disengage feature if the wiper arm is restricted so you don't shear the splines. If so, the wiper will be free to move if you try to sweep it by hand over the windshield. Open the cover over the base of the wiper arm, should be a nut there, place wiper in the park position you want, tighten the nut and the arm will be re-engaged.