Mercedes B-Class Windscreen
Washer Problem
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Not long after I bought
my Mercedes B200D I noticed the windscreen washer was pretty
poor and after a few years was only producing a dribble. In fact
a couple of years ago my MoT failed with "Windscreen Washer
inoperative.. needs filling" or something similar. As a
rear tyre was damaged, this was replaced and the car passed its
test (with an "empty" reservoir). A year later the
MoT guy didn't notice the poor windscreen washer or similarly
decided it just needed topping up so I had no trouble.. that
is unless you really need one's windscreen properly clean. When
we decided to take a bottle of water with us recently on a long
trip I decided I must fix it.
Youtube wasn't much help and I decided to fix it through
investigating the problem myself. In fact,
because mice had ravaged the wiring a few years back I'd
already formed the opinion it was a gnawed-through tube that
was the problem and vaguely imagined fitting heatshrink tubing
over any damage. Under the bonnet I found some of the washer
tubes which actually looked OK and pretty tough and I'd already
looked for evidence of water leaks or drips under the car and
found nothing. I'd also completely filled the water reservor
and tried the washer button. In fact by now even the dribble
had gone and I could hear the washer motor whining away to no
avail. The rear washer had also completely failed as well I should
mention.
So, with no real alternative,
I jacked up the car and removed the nearside front wheel. I then
noticed a detachable panel roughly where I imagined the washer
pump was located so removed this hoping to see enough to make
repairs but promptly dropped it behind the wheel arch cover leaving
me little option but to remove the whole cover (something I'd
already planned to do anyway). |
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Above, with the wheel
arch cover removed, you can see the windscreen washer reservoir
(that large black plastic thing). Those water stains are from
over-filling before I'd started. The pump is clipped into the
side of the container and has two black plastic tubes connected.
Also, on the left of the pump, is the fitting for detecting the
reservoir is empty and on the top of the pump is its two-wire
power plug.
I unclipped that nearside tube
by slipping its black plastic clip upwards and tried the washer
to see if water was ejected. No water dribbled out and worryingly
the pump wouldn't come on. In fact the wipers wouldn't work either
and I was then concerned I'd disturbed and broken another mouse-gnawed
wire so rummaged under the bonnet trying to duplicate my initial
pulling and prodding of tubes and wiring then tried the wipers
again. Still no response and then I suddenly realised the bonnet
being open might be the reason for disabling the wipers. Sure
enough, closing the bonnet brought the wipers back to life and
surprisingly no water was emerging from the pump from the hole
from where I'd detached the tube.
Was the pump blocked up so I
decided to remove and test it? Maybe the frenzied whining wasn't
indicative of a working pump.. maybe something had bunged up
or come adrift inside? Despite pulling and levering it the pump
remained loosely fixed in place although I could lift it just
enough to pull it out from the reservoir output hole. |
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I realised something quite
odd though.. despite sliding the pump upwards and clear of the
reservoir, no water emerged ..... not even a single drip. Maybe
there was a rubber valve in place which only allowed water to
be pumped out once the pump was plugged in? I resolved to remove
the pump and I realised I had no option but to just pull it until
something gave way. I detached the power lead by levering under
the lower edge of its plug and lifted the pump to its highest
position free from the reservoir output hole and pulled very
hard on the pump body. There was a loud "pop" and the
clip around the pump body detached itself from a mating hole
in the reservoir and the pump was freed albeit with the leftmost
tube still attached. In fact the clip on this tube was different
and looked fairly secure and immovable so I left it. At this
point I'd assumed the nearside tube I'd removed was for the rear
washer and the other was for the front. This turned out to be
wrong and almost certainly it was the way air could get in to
avoid producing a vaccuum.
I filled a container with water
and made sure the pump input tube at the bottom was below the
surface and got my wife to start the car and press the washer
button whilst I watched the hole from which I'd removed the nearside
tube. No water emerged so I shouted to stop and try again. The
pump whined away and again no water emerged so I shouted to stop
again. The pump clearly wasn't pumping.. but no .. in fact the
windscreen was being drenched in water.. twice, but I hadn't
heard the shout of glee above the engine noise and pump whining...
So.. the pump was fine and I
turned my attention to the hole in the bottom of the reservoir.
There was a rubber thing with a hole in the centre. I decided
to investigate (I'd assumed it was a valve) so pulled it out
which was accompanied by a vertical jet of water. I put my finger
over the hole in the reservoir and peered at the rubber valve
fitting. It was coated in black gunge. I rubbed some off and
noticed some really tiny holes. So, it wasn't a valve but merely
a filter. I wondered about the contents of the reservor and decided
it would be best if I just let it empty and scour any gunge left
inside so removed my finger and let it finish emptying.
I examined the filter and found
its loads of microscopic holes were blocked so carefully cleaned
the thing in running water until all the holes in the base and
slots in the sides were completely clean. |
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Apologies for the blurred
image on the left but you can see the number and size of the
holes compared with a published picture of a replacement on the
right showing larger less-blockable holes.
Is this perhaps an example of
a design problem? Too many owners filling the reservoir with
none-to-clean water or from a garden hosepipe with contaminants
from degraded material leading to complaints? |
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To be safe I extracted
all the water from the bottom of the reservoir with a sucker
in case it was mucky. It wasn't and after fitting the cleaned
filter and re-fitting the pump I tried the washer. The pump whined
very loudly and nothing happened except for a warning on the
screen "Refill windscreen washer" ... oops I'd forgotten
to fill the reservoir so carefully added a bucketful of clean
water with a spot of Fairy liquid and on a second push of the
button (with the bonnet closed of course) the windscreen was
completely drenched from the three jets. Now to fit the wheel
arch cover (below). |
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Refitting the cover is
a really messy job whilst lying on a gravel drive with minimal
clearance under the car and, after pushing and pulling with limited
luck, I couldn't fit the last few screws so gave up (the other
16 screws should be enough). The wheel was also difficult to
fit. Some are easy but this wasn't... probably because I hadn't
bothered to turn the steering back from full left lock and the
wheel was exceedingly heavy and awkward to grip.
Hopefully this story will be
discoverable and be of use to other Mercedes owners who perhaps
will be blaming the pump or contemplated getting a garage to
diagnose and remedy the fault? Material and parts costs zero,
labour priceless! |
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