Electrics: Rear window washer

[currymunster]

My wife has just started driving the 2004 XC90 now that I've fixed a lot of the issues.
She just came in though and said she can't find how to turn the rear window washer?
I went and investigate and the switch on the end of the right stalk turns the wiper on to constant or intermittent.
Pulling the stalk toward myself does the front washer and wipers.
Pushing the stalk away from me does the front washer jets and starts the rear wiper with no washers. I'm guessing there is something awry here.
I assume pushing away from me should start the rear wiper and washer jet and someone else has been here before me.......
Anyone had this before.... Maybe a plug put back the wrong way around. This could be a can of worms maybe??

[Moose Test]

Yes, something isn't right. Pushing the stalk away from you should operate the rear wash and wipe function.

IIRC, there is just one washer motor for both front and rear windscreens and so I'm guessing that the front or rear selection changes the polarity and hence direction of the motor, which, in conjunction with one-way valves determines the direction of water flow from the reservoir.

As you say, it might be worth checking the connection, although I'd expect most connectors to be polarised. If I'm correct and there's a reversal mechanism to select the water path, maybe a one-way valve has failed.

[Tannaton]

On early model XC90's there are 3 washer pumps attached to the reservoir, one for the front screen, one for the rear screen and a larger once for the headlight system.

I think (rather than know for certain) that they went to a 2 pump system (one for rear and front screens, one for headlights) in MY2005 so yours could be either depending on build date.

FYI the washer bottle is the most elaborate plastic moulding I have ever seen, each pump is run off different chambers at different places so if you run low on water the headlights stop being washed first, then the rear, then the front....

Dropping the washer bottle is relatively easy - once you know how! It's behind the bumper on the drivers side, you peel off the front bumper cover and then you need a socket & extension to undo the mounting bolts that pass through it.

It's worth doing as at that age it's usually full of slime and the pumps have filters which are clogged, very satisfying to see the improvement after a good clean....

[currymunster]

Originally Posted by Moose Test

Yes, something isn't right. Pushing the stalk away from you should operate the rear wash and wipe function.

IIRC, there is just one washer motor for both front and rear windscreens and so I'm guessing that the front or rear selection changes the polarity and hence direction of the motor, which, in conjunction with one-way valves determines the direction of water flow from the reservoir.

As you say, it might be worth checking the connection, although I'd expect most connectors to be polarised. If I'm correct and there's a reversal mechanism to select the water path, maybe a one-way valve has failed.

Thanks for the responses and help. I'm working tomorrow but I should hope to have time to look at it on Sunday.
I'll let you know what I find.
Good help on how to remove. Thanks.

Edit....I thought I'd quoted both of you but it didn't work properly.
No favoutism....I promise.. 😁

[currymunster]

Originally Posted by Tannaton

On early model XC90's there are 3 washer pumps attached to the reservoir, one for the front screen, one for the rear screen and a larger once for the headlight system.

I think (rather than know for certain) that they went to a 2 pump system (one for rear and front screens, one for headlights) in MY2005 so yours could be either depending on build date.

FYI the washer bottle is the most elaborate plastic moulding I have ever seen, each pump is run off different chambers at different places so if you run low on water the headlights stop being washed first, then the rear, then the front....

Dropping the washer bottle is relatively easy - once you know how! It's behind the bumper on the drivers side, you peel off the front bumper cover and then you need a socket & extension to undo the mounting bolts that pass through it.

It's worth doing as at that age it's usually full of slime and the pumps have filters which are clogged, very satisfying to see the improvement after a good clean....

Just because.....😁😁

[currymunster]

Spent some time on it and problem diagnosed.
It needs a new pump.
Although the pump works fine!
Someone had already looked at the alarm and the inner wedding is not back so I was able to access it that way. I'm sure it saved a lot of time.
For clarity this 2004 D5 04 plate has no headlight washer system.
One pump for both the rear and the front.
I make an assumption that the pump works on a reverse polarity.
There is a washer between the two outlets that should be central.
When one side has pressure it forces it over to block the other outlet.
Because the front gets used more the washer has become forced permanently over blocking the rear outlet. If I turn the washer over it then only works on the rear jets.
Due to the design I am assuming the washer is part of the pump.
Hence why a new pump is needed.
I will post pics once I've compressed them.
Also I see a tyre has worn the inner wing??
It's not doing it now. Although the tyres are bigger than standard from the previous owner (255/55/18)

[currymunster]

Pics for you

[currymunster]

Pics again

What I don't understand is if it is reverse polarity why does it need the washer.
If it isn't then I really don't get it....

[Moose Test]

I think you have it already worked out in your previous post. The washer acts a one-way valve, ensuring that only one outlet passage is ever open at a time when the pump is running. If it spins in one direction, water exits on that side of the pump and pushes the disc across the aperture on the other side without flow (due to differential pressure), and vice versa.

Yours is sticking and doesn't (without your help) move over to seal off the front outlet when it should. Water pressure takes the path of least resistance in either the common t-pipe or impeller chamber of the pump, and flows to the front, regardless of motor direction.

Without the one way valve action, the whole scheme falls apart.

[currymunster]

Originally Posted by Moose Test

I think you have it already worked out in your previous post. The washer acts a one-way valve, ensuring that only one outlet passage is ever open at a time when the pump is running. If it spins in one direction, water exits on that side of the pump and pushes the disc across the aperture on the other side without flow (due to differential pressure), and vice versa.

Yours is sticking and doesn't (without your help) move over to seal off the front outlet when it should. Water pressure takes the path of least resistance in either the common t-pipe or impeller chamber of the pump, and flows to the front, regardless of motor direction.

Without the one way valve action, the whole scheme falls apart.

What I don't understand is the pump has two outlets. So why does it need the valve thing. Pumps one way out of the left outlet. Pumps the other way, out of the right outlet. Why do they join with a valve?
I know I'm missing something and it's there for a reason. It bugs me when when I can't work it out! 😡😡