Rear window wiper always on

[Dutchyankee]

The rear window wiper on our 2004 Viano Marco Polo spontaneously started and only stopped when I removed F7 from the main fuse box. The washer function still works but normally it goes in intermittently when it is activated by the switch or washer button.

I’m thinking the issue is in the wiper motor assembly (M6/12) which is a relative easy replacement. See attached schematic.
Has anyone ever experienced this?
I will contact my local dealer for a price estimate and delivery time.
Thanks in advance

 

[Pete S]

How nice to find somebody else with an older MP! The always-on wiper problem happened to us on the way home from purchase of our 2006 model three years ago, and I also ended up removing the fuse. The solution (as determined by our local MB dealer) was to replace the wiper unit, which has worked fine since. I'm sure there was some tiny cheap microswitch inside the unit that had failed and should have been replaced, but we just don't fix stuff that way any more, not even on 20 year old vehicles!

 

[Dutchyankee]

Hi Pete,
Thanks for your reply.This is the second one.
I openen one of the €250 wiper motor assembly and found corrosion on the pcb due to leaking washer fluid connection.
After cleaning the short ( see photo) and adding a protective layer grease as well as a couple of o rings at the water fitting I think it’s time to tear the back apart to replace it with my “self revised “ and improved motor assembly.
I was working ok until one day I decided to use the washer function. And as expected, 2 days later it started to turn on intermittently then permanently.
So F7 out and waiting for some reasonable weather to do the swap.
I’ll keep you posted and I have a series of before and after photos of the inside.
I also suspect the internal relay but well see.
Cheer’s,
Stephen