Why does my rear wiper fuse keep blowing?

[John Brennand]

Update chaps:

Just braved the elements and guess what.... its working now. Fuse hadn't blown. So hoping its something simpler. Third faulty wiper motor in a row? Bad connection in the connector?

More investigations after the deluge.

[John Brennand]

Having thought about it a bit. I thing my diagnostics might have been a bit off. With it working fine now - clearly the fuse isn't blown and thinking back I never actually looked closely at the fuses I took out I just assumed they had blown after seeing the very first one had.

So if we assume the issue isn't a blown fuse does that change anything?

Surely a shorting wire would blow the fuse first ? I was wondering whether it might just be a loose connection - say on the motor's cable connector (or somewhere else)? I will take a look soon. Or perhaps I have just been unlucky with the 2 replacements I got - should I try a third?

Thoughts/ramblings appreciated.

[Harley Dave]

It's working now - keep using it until it stops working, then check the fuse (properly - with a continuity tester or similar)

At that point you will have something to go on.

Cheers

Dave

[John Brennand]

Originally Posted by Harley Dave

It's working now - keep using it until it stops working, then check the fuse (properly - with a continuity tester or similar)

At that point you will have something to go on.

Cheers

Dave

Kinda what I did. It stopped working, I pulled the fuse, looked at it with a magnifying glass, looked perfectly intact, but put a new one in anyway, switched it on and it was still dead and not working. left it overnight went back, switched it on to double check and it started fine, ergo... fuse ok.

[Harley Dave]

Hmmm - motor overheating and seizing perhaps.

Then, when cooled down, works OK again??

Run the wiper for a while (perhaps with the wiper off the glass) and see what happens.

Also run the wiper and feel how warm the motor gets.

When the wiper stops, are you getting 12 volts at the motor?

Have you tried running one of your spare motors on the bench?

Could be the wiper linkage is stiff/seizing up ?

Cheers

Dave

[John Brennand]

Originally Posted by Harley Dave

Hmmm - motor overheating and seizing perhaps.

Then, when cooled down, works OK again??

Run the wiper for a while (perhaps with the wiper off the glass) and see what happens.

Also run the wiper and feel how warm the motor gets.

When the wiper stops, are you getting 12 volts at the motor?

Have you tried running one of your spare motors on the bench?

Could be the wiper linkage is stiff/seizing up ?

Cheers

Dave

What's odd is that I have had 3 different motors display the same behaviour. Could have been unlucky I guess or something is causing the same problem to reappear.

[Harley Dave]

Common factor could be the linkage - or, of course, the wiring.

But that's more likely to happen when the wiring gets moved around - either while driving or opening/closing the tailgate.

Cheers

Dave

[SwissXC90]

^^ this

if the problem is that the wiper motor simply doesn't work sometimes, then suspect a wire breakage in the flex part of the wire loom from tailgate to vehicle body.

The loom bends every time you open and close the tailgate
Any eventually metal fatigue breaks wires - and sometimes they sit just right that they work.... and then the next day they don't touch and the motor doesn't work....

Slide the rubber boot back and visually inspect. Any breakages / fatigue will be easy to spot.

And where one wire breaks, others follow soon after....

[John Brennand]

Originally Posted by SwissXC90

^^ this

if the problem is that the wiper motor simply doesn't work sometimes, then suspect a wire breakage in the flex part of the wire loom from tailgate to vehicle body.
...

Thanks Swiss. I am no electrician, but if there is a broken or shorting wire somewhere wouldn't that just keep bowing the fuse?

This post has an unfortunate title as I have established that apart from the very first occasion I have no real evidence that they are repeatedly blowing - I just assumed they were after the first one. Indeed, after the wiper stopped last the fuse I replaced wasn't blown and the wiper worked fine when I tested the next day.

I do recognise the tailgate issue as it condemned my old 245 to the scrapyard in the sky and I had to have my old XC70 wires repaired for the same issue, buy the good Mr Mike Alder of this parish. I just thought that it was "less" of an issue on the XC90 due to design changes.

But of course I will take a look.

[SwissXC90]

As the wire flexes when it moves, it might sometimes make no connection and not cause any shorts, or it may sometimes make a connection and the motor works, or it may sometimes touch other wires and cause the fuse to blow

I've seen all these scenarios with my own eyes before
Anything can happen with broken wires inside a flexing wiring loom.... it all depends on how many are broken and how they are broken....