The other day I noticed that my rear wiper wasn't giving a full sweep across the back window.
When you use the wiper - either a quick flick or leaving it turned on - it should give a double-sweep and end up back in the starting position.
The double-sweep goes 180 degrees one way, then returns 180 degrees the other way, to end up where it started.
But my wiper was only going about 2/3 of the way across on the first sweep and then stopping. I could hear the click from the relay to start/stop the movement of the blade.
Then the next movement would complete that first sweep and then start the return sweep, again stopping partway through. The third sweep would often complete the whole double-sweep and leave it back somewhere near to the starting position, but this was not always guaranteed - if I absolutely wanted it to end in the starting position it could take up to 7 attempts.
It's probably better to describe if you imagine that your rear window is the top half of a big clock face, and you are standing at the rear of the car looking at it.
The wiper blade normally rests at 3'o'clock.
When everything works normally the first half of the sweep moves anti-clockwise back through the hours on the clock face from 3, 2, 1, 12, 11, 10, 9. Then the second half of the sweep returns back clockwise through the hours on the clock face from 9, 10 11, 12, 1, 2, 3 where it finishes - back where it started.
But on my car the first movement went 3, 2, 1, 12, 11 and then it stopped at 11. The second movement went 11, 10, 9, 10, 11 and then it stopped at 11 again. The third movement went 11, 12, 1, 2, 3 and then it stopped at 3 or thereabouts.
So in the time it would take a normal wiper to do 3 full double-sweeps, mine was doing just 1 full double-sweep but in 3 seperate parts.
A guick search of the forum showed that quite a few people have had this problem, and suggested fixes included a loose nut on the wiper arm, faulty wiring (from the roof to the hatch), faulty column stalk, or a faulty control unit (as simple relay change appararently isn't possible).
I wasn't able to check any of these, apart from the nut on the wiper arm which was tight and secure.
[u]But here's the thing[/u]: at the exact same time this wiper problem started my electric mirrors also stopped adjusting, and my reversing light stopped working.
The mirrors and reverse light are both on the same fuse beneath the glovebox (no. 63, 10A). This was my first point of call, as Mrs PM needs to adjust the mirrors when she drives the car. According to the handbook this fuse has nothing to do with the rear wiper.
So last night I changed the fuse for the mirrors/reverse light (which had indeed blown) and they now both work perfectly.
But bizarrely the rear wiper now works perfectly too! It does the full double-sweep back to the starting position, exactly as it should be!
I have no idea how one should affect the other, and fuse no. 63 was the only thing I checked or changed.
So if you have similar problems with your rear wiper, maybe you could check fuses that are not associated with the rear wiper, as a problem elsewhere may be causing interference.