Hi everyone!

Right after a bad crank pulley and an MAF sensor that took the car sitting for 3 weeks, I have been blessed with the RCM / K40 symptoms (dash and lights working but no crank and within few seconds motor Fan running like a P-51 Mustang while taking off) (and surprisingly disabling OBDII recognition by my diagnosis tool (Launch 129x pro, always recognizes VIN when plugged to the car and start diagnosis)).
After this event, occasionally no crank isolated symptoms that I didn't gave relevance (usually turned key off and on and started right away).

So turns out I'm in need of a new Engine Control Relay*
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As American Zettler-AZ970E-1A-12D is almost impossible to find where I live without paying an absurd amount of money, and while I search for another candidate** for soldering in place of the bad relay,

I thought that a simple solution would be to jumper the relay with some sort of analogic switch, acting as a Killswitch, mounted in the cabin, or in a "secret" place, as an additional security measure.
To be actuated by hand right after turning key to ACC, before cranking, or even before inserting the key, just like the rubberband trick did
Could this be done without damaging the ECM, SKREEM or any other electronic module? (Maybe because electrostatic when switching or something that my sparingly knowledge of electronics didn't thought about)?

And even overcomplicating it (I'm always disregarding the KISS rule -Keep It Simple, Stupid :P), could that Engine Control Relay be substituted by those generic battery Killswitches (200A, 12vdc SPST NO relays that can be activated through a 433mhz remote)?, and stuffed into RCM box to go completely undercover (pun intended).

Given that #3 relay disables completely cranking, OBDII tampering, and also runs fan in a deterrent way to anyone wanting to run away with the car unnoticed, and also that my siren went bad (didn't bought another one yet), and having in my near-future to-do list of XFire mods an SKREEM delete (through one of the various options listed in this marvelous forum, when the budget jar is full again), I'm a bit concerned about how vulnerable I would render the car with all this mods that overrides security, so, just to be cautious.

Thanks in advance, have a nice ride!!

**Possible RCM relay candidates:
Since RCM modules can go up to +100$ shipped to my place, and I'm short of budget atm, I thought to buy and salvage Pulse Module relays (can get the PM about half the price or so).
Also found in the comments section of a YouTube vid (htt ps://youtu.be/spTx0k3_PI0?si=3T0zRpDaQMU202vH) a list of candidates by the user antdavisonNZ that I'll copy-paste here if is useful for anyone, if possible to be confirmed by the experts or by comparing data sheets.
Euro footprint, 90ohms 1.6w:
Tyco TE Omron P&G OEG Schauk -- V23076
Multicomp HKE CMA4
Song China -- 822
Fujitsu Takimisawa -- FRL-274
CIT --- A5 (a51ae12?)
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I will summon all the 2 legged pools of crossfire knowledge that I can remember just in case. All opinions are welcomed!@tighed1 @pizzaguy @GraphiteGhost @zip439 @onehundred80 @Valk @Viper-666

 

Yea, the coil goes open in those relays from time to time. I find the best option is to order a new RCM, then get the old one fixed when I can. OVer here in the USA, I just send mine to DJ. He has a huge inventory of those relays, the secret is to by them in lots of over 100, they get cheap then.

I would not go to the trouble of a "kill switch", if you have the OEM SKREEM/ECU system from the factory, there is no need to add anything to it. One thing you can do, in order to move the car, is to wrap a rubber band around the relay, holding it closed, so the car will start. But you must remove that rubber band once you move the car and turn the engine off.

For an RCM., it is often less expensive to search for: "2003 Mercedes SLK320 Relay Control Module" than for a Crossfire part. IT's the same part, but many warehouses do not realize it's the same part.

 

Here is the standard relay for our cars at amazon in Germany: Here is just a relay ( I think this is tighed1 selling relay only) Zettler AZ970E
I think it is better to repair or replace RCM and fix it correctly. If you start adding more to the mix of electronics already in your car you create additional problems when trouble shooting.

Contact the seller at the ebay Zettler AZ970E link above and check what it will cost to mail you the part. Should save you a good bit of money.

 

Thanks for the inputs gentlemen!
Zip I'll check these links of the official relays!
180 thanks for the advice about the all RCM, I'll check that too. (Probably a better option than buy a pack of 100 relays, I hope not having to repair the RCM 99 times more! )

As for the Killswitch itself, yeah maybe you both are right and it's overcomplicating things, but I read so many SKREEM nightmare stories here that getting rid of it prior to the failure , plus having an alternative for added security , it's something that often come to my mind, considering that our cars have 20 yrs and electric modules fail over time and substitution gets a bit complicated...

​​​​​​Skreem seems like a ticking bomb to me, even following your advices regarding electric care of it as not jump starting/be jump started, using a booster, etcetera

BTW, I posted the thread in /All XF having in mind that everyone has an RCM, as a possible Killswitch location, given that I found just a pair of brief references in my previous search for related posts
But if mods consider it's better for it to be here, as is related to an RCM failure, it's ok to me of course, move it wherever could be more useful to the community.

I'll update post with the repair results, in case it may be helpful for anyone.
Thanks to y'all. Have a nice Ride!
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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