I added 4 additional comments to desoldering an open circuit relay in k40 RelayControlModule, and replacing it with a us$5 readily available relay shipped to me in New Zealand from Australia in less than 24 hours, the additional comments list the exact part number I used, rather than just the manufacturers family part number, and some commonly available alternatives

http://www.youtube.com/watch?v=spTx0...wiBA4QSzs0dpRU

The hardest part is to remove the old faulty relay since the metal frame soaks up a lot of heat, the replacement part has the same footprint as the OEM benz part, but comes in a 2 piece plastic housing which needs to be removed to avoid interfering with the brass bus bars, so essentially these are the same as the Zettler open frame relays, but in a plastic case, make sure you buy the EURO footprint version, the US footprint version has different leg spacings and won't fit into the PrintCircuitBoard solder points

my original post in the slk230 forum fully discussing my cheap fix is at
http://www.benzworld.org/threads/slk...0-box.3113639/

hope this helps someone
hi from NZ

EDIT : the radiator cooling fan running at 100% is not a relay problem, but bad solder joints at one of the corners of the PrintedCircuitBoard
In this image ..
https://www.benzworld.org/attachment...1-png.2806235/
.. you can see the position of the joints, extreme top, extreme left, the row of 3 joints
The modules were made with non-leaded solder, so not as reliable as lead solder, just resolder those joints with a big soldering iron and lead solder, and the fan will go back to normal speed, and car will start, super common problem
I made that image from datasheet drawings of alternative EURO footprint relays composite over a scan of the RCM PCB before relay purchase to make sure they had the same leg spacings