Rear Window Washer Not Spraying
 

Recently I have purchased 2000 ML430.
There is nothing coming out from the rear window washer nozzle.
The wiper works fine. The rear pump works fine. The washer reservoir is full.
Here is what I've tried so far in order to troubleshoot:
- I disconnected the rubber hose from the rear nozzle and the rear pump.
- When I blow air from the pump side, nothing comes out from the nozzle side.
- When I blow air from the nozzle side, the water flows at the pump side. :word:

I can’t locate any valves (that might have blockage) between the pump and the nozzle.
Are there any?:confused:
Any help or ideas are appreciated.
Thanks

Here is the diagram for the rear windshield washer system.
It seem that the problem is with the control valve (item #8 on the diagram).
I did trace the hose from the pump to the firewall gromet (item #11 on the diagram) and a bit after the gromet near the stearing column on the cabine side. I didn't find any valves.
I wonder where physicaly this #8 check valve is located? Does anyone knows? :confused:

Just for the future inquiries regarding the location of this check valve...
It's behind the C-pillar cover, adjacent to the seat belt height adjuster.

I had the same problem, make sure the hose for the washer fluid is not blocked in the gap between the chassis and the rear lift gate. it might seem fine when you open the tailgate, but once you close it, it will squeeze the cable. I had to remove some of the insulation covering the hose to clear the blockage.

The blockage of the windshield washer check valves is quite common, specially in a 15 year old vehicle.
It may be due debris, dishwashing soap hardened, or just the soft rubber tube inside the check valve that is getting a bit stiff as it ages.
The check valves can be replaced easily, any brand and model of windshield washer valve that fits the hose diameter will work fine. Actually an upgrade will be welcome, since the original design of these valves is not the best.
But you can dismantle the old valve and give it a few more months or even years of life.
I did it and it's working well for months.
It's a bit trick to open it without destroying, but with a thin screwdriver and some patience it can be done.
Sometimes a good cleaning is enough, but if the little rubber tube got stiff, there's a workaround. Just make four cuts on the rubber, turning the tube into four flaps, as shown on the diagram below.
During the reassembling position two oposite flaps over the holes on the center tube.
Blow some air to check if it's opening. If not, make the cuts longer, but do not cut through the sleeve, since it seals the valve when reassembling it.
Be carefull to not rip and destroy the rubber completly, nor just take it away, otherwise the valve may leak inside the vehicle.
If you have done it right now you get a working valve again. ;-)

https://cimg8.ibsrv.net/gimg/www.mbw...bb83f768d4.png

Four cuts on the rubber tube inside the check valve.

Saved the day
 

Thank you all for helping me out of a tight spot. I wouldn't have found that check valve without that picture Yober37, that saved me hours of frustration after already looking under the rear hatch trim to no avail. Hopefully this thread saves someone else from my mistake. For anyone else looking at this old thread, its a good idea to gently blow through the hose after the check valve so as to hopefully dislodge any bits of grit that are stuck inside the rear nozzle. If it helps, the front check valve is located right under the cowl next to the driver's side nozzle. I had to blow through it with the air hose to free it up, whereas the rear one was completely plugged and I had to take it apart to clean it. One final note - the check valve for the rear washer was full of disintegrated rubber from the inside of the hose. Hopefully later years were fitted with higher quality tubing (this ML is a 2003), but I noticed that the inner layer of the hose at the pump connection was beginning to rot and of course it made its way to the valve. I don't think there's any easy fix for this other than replacing the whole length of tubing or running a new piece through the car. Hopefully no one else's washer lines decide to crumble from the inside. Anyway, cheers and thanks all for the good advice.
Josh

Where is this mysterious valve?
 

Man, this issue is driving me crazy.
so I've already replaced the pump and snipped the hose since the end was freyed and started to leak.
1 year later the rear washer stops spraying. I blew out the hose where it connects to the pump as well as from the rear tailgate where it connects to the nozzle .also pulled apart the nozzle and blew it out. I tried taking the C pillar off on the passenger side but did not see anything other than the seatbelt assembly. Can anyone provide some more info as to where this little bugger is hiding? Also, is there any easy way to remove the C pillar without having to take apart the whole rear panel? It was such a headache.
Thanks!

https://cimg0.ibsrv.net/gimg/www.mbw...85c91a2b10.jpg
Have you disconnected the hose from the rear pump motor and see if the motor is squirting out fluid?

The only location I can give is what EPC is showing. Find the grommet at the firewall and just beyond that should be the check valve.