Windshield wipers work on all but highest setting (2012 Prius)

I have the exact same thing - wiper works but not the highest speed. Have anyone solve the problem?

 

There's a troubleshooting chart, page 5710, "front wipers do not operate on HI", in this attachment. The links are dead, but you ou can then search for "inspect the windshield wiper motor assembly".

 

EDIT: Found robomoto's posts on cracking the wiper motor open and cleaning it out. I'll give that a shot in the morning.
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Hoping someone might be able to help out on this. Having the same symptom: wipers won't operate at all on HIGH, and the LOW setting is - strained and slow. I had to manually assist it to get it to move on LOW a couple of times.

I've disassembled the wiper motor and the wiper transmission. I did troubleshooting on the motor. It runs (seemingly) properly on all settings, including HIGH, with the motor detached from the transmission. However, with it attached to the transmission, nothing moves on HIGH, even with the blades detached.

So, I'm still in the dark as to whether it's the motor or transmission. The transmission offers a fair bit of resistance to movement, certainly more than I'd expect. Given the gradual decline into failure, I'm thinking that's the issue. Has anyone successfully disassembled the transmission and lubricated it?

 

Funny things can happen with wipers.

The carbon brushes can be worn in the motor. Sometimes that's it.

Friction in the transmission can be a thing. Don't forget the double-jointed passenger-side wiper arm. There are two bearings in it and they're pretty weather exposed. One time that was noticeably slowing my wipers down. Was as simple as taking that arm off and spraying some light lube into those two bearings, and working them back and forth a bunch.

The most recent time my wipers stopped working was just a few months ago, and it was just tarnish on the blades of the wiper fuse. The fuse was otherwise fine, and since getting its legs shiny again with a rubber eraser and putting it back, the wipers have been fine.

Figuring my car might now be getting to that age, I now carry said rubber eraser in the glove box.

That's all to say, look at all the possibilities, don't rule anything out without checking.

The rubber-eraser-to-polish-contacts trick was a recommended one that I learned decades ago. I do remember recently seeing an article (probably for some modern contact cleaner chemical) that said "never use any kind of eraser! they're too abrasive!"

I don't know. The one I'm using is a white art-style polymer eraser; I like it better than the pink ones that leave crumbs. I don't know how microscopically abrasive it is or isn't, but for me it gets the job done, and doesn't leave the contacts visibly scuffed up, anyway.