Wiper arm stopped working

There is one motor for both, and a linkage connecting them, under the cowl louvers. Also, your passenger wiper arm is the big odd double-jointed thing, which has a couple bearings in it (under that streamlined top cover that's kind of hard to remove, but you don't have to, because they're easy to see from below when you take the arm off).

When my Gen 1 hit about 14 years of age, I noticed my wipers running slow and squeaking and it was those two bearings. I just took a guess with some lubricant I had around and squirted it in those bearings (from the bottom, after taking the arm off), and that solved the problem. (I think I used an ancient spray can of Aervoe Tef-Lube that some bike shop sold me back in the 1980s. It has followed me through three moves.)

If I had to guess with yours, my guess would be that those bearings in the passenger arm got worse than mine did, and the arm got so difficult to move that the linkage under the cowl louvers probably popped off at one end.

So, fixing it will probably also be a two-step affair. You can take off the passenger wiper arm, and find some likely lubricant and see if you can get those two bearings moving freely again (or pitch it and buy a new arm), and then take the cowl louvers off and try to see what let go in the linkage, and whether you can pop it back on, or need to replace it.

If you look closely at the windshield glass, you should see a little round dot manufactured into it, right where the end of the wiper blade points when the wipers are parked. At least my Gen 3 has that. It's helpful when putting the arm back on.

 

There is another possibilty besides a disconnected wiper linkage. The passenger side wiper has two pivots- the left one drives the arm while the right is an idler that moves freely and guides the wiper. A nut holds the left arm link to the splined stud that drives it. If that nut works loose then the wiper won't move. So check if the nuts on the pivots are tight.

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It might still be worth checking the condition of those bearings; I've not heard much about that nut just coming loose for no reason.

Also, whenever a wiper arm is removed, Toyota suggests using a wire brush to clean up the matching splines or serrations on the driving shaft and in the arm, get any metal grindings out of there. Brushing up and down, of course—along the splines.



If yours has been slipping for a while with a loose nut, those areas might be nearly nothing but metal grindings by now.

A good vigorous brushing will show you if there's much spline action left there at all, or if it has all been just nearly ground flat.

If the splines are too far gone, it is likely to just work the nut loose again; solution: new arm and linkage.

If the splines clean up ok and the two bearings in the arm easily move, you can carefully put the arm back on and, ideally with a torque wrench, tighten both nuts to 15 or 16 foot pounds (21 newton meters).

'Approximate' tightening (by somebody) may have been how this situation arose in the first place.

 

I guess one way to get a sense what the splines should look like would be to take off the driver's arm too (which presumably hasn't been slipping) and compare to those. They're not super deep even when fresh, which is what makes them a bit delicate and easy to flatten if not careful.

Then of course they get the wire brush treatment too, before replacing the arm and carefully retightening to 15 or 16 ft lb.

One of the real tricks putting a wiper arm back on is that what you want to do is set it down on the shaft so gently you can feel when the splines mate up, and then hold it steady in that position while tightening the nut, not letting the arm rotate (because that would flatten the splines). But the arm's got this big spring in it, which nearly keeps both your hands busy just trying to keep it down flat on the shaft.

 

I noticed the splines (on our 2010) looked a little "chewed". This is after maybe 3 removals, and we're low miles. Maybe the metal is too soft??

 

I think they make the splines very fine, because the arms are quite long and you want to be able to position them precisely to point right at the little dots when the wipers are parked. If the splines were more robust (⇒ coarser), you wouldn't have enough position choices. So they are very fine, and easy to mash.

I've never owned a vehicle where they weren't like that; I think it's just the nature of the beast.

Steering wheel splines, same deal.

 

Usually the arm that the splines mate to is smooth die-cast "pot" metal. When it's all tightened up the splines dig in to the arm and create matching splines. What I often see is in freezing weather (ice, snow, sleet) that the arm can't move but the mechanism tries and something has to give.
That said, the OP should check for smooth movement of those secondary pivots.

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