electrical gremlins w209 clk convertible

[Ted]

Try fuse 9 in the rear fusebox (behind a cover in the boot on the nearside).

 

[ex4x4]

so... armed with electrical drawings - disconnected plug connection on rear SAM where the alarm siren and tow away tilt sensors are plug in( all on same plug) and reconnected a fully charged battery. all systems working again.
proved out alarm disconnected by lowering drivers window and then arming alarm. after a few minutes - waved my arm into car interior and nothing happened.
But then as usual - key fobs not recongnised/not functioning, and windows forgeting where they are supposed to be, instruments not working etc etc - all the usual faults althought battery voltage remained at a healthy 12.8V.
Disconnected battery for an hour then retried all the above with the same result. Its as if a few moments after battery connection and systems reset - the system goes haywire and forgets all its settings.
But I think Ive sorted the parasitic draw by disconnecting SAM plug.
onwards................

BTW i have taken photos throughout ( sam connections, parasitic drain test procedure etc) and once all sorted Ill write up a full blown report as it will most porabably be of use to folks with similar issues.

 

[Eddy77]

Could the Sam unit into which the alarm plugs be duff and sending crazy messages to the main ecu?

 

[ex4x4]

Yes I was thinking along those lines .I'll pop it out and give it a good looking at. There doesn't appear to be any evidence if water ingress in the surrounding area and the Sam casing is free from water marks etc but you never know. ....

 

[ex4x4]

So - I finally got some time to remove the rear sam and inspect it.
Unplugged all connections and removed from car.
Removed all fuses and relays and began taking casing apart.
These things were not designed for taking apart!!!
The rear cover comes off easy enough - but only to reveal the bottom of the main circuit board, with all the components hidden underneath.
I noticed some freshly soldered connections ( very neat - professional like) but could not see what it was that had been replaced.
I began taking the rest of the casing off - what a job - even harder to put back on!!
I found what looks like some kind of white cubic relay or transformer type unit ( no part numbers visable) in the middle of the main board had been replaced. But more importantly - a capacitor had been damaged and leaking a small amount of oil like substance.
Now Im not sure if the it was damaged by my removal of the casing - or as a result of the previous repair man taking apart the casing.
I purchased some new 470yf caps and replaced the damaged one on the board, then spent the next hour or so modifying the casing to allow it to be put back together without risking damaging the capacitor again.
So now all back together and back in the car - and battery reconnected and , touch wood, has been working ever since ( approx 6 hours) without the recurring concerns with central locking / windows etc etc forgetting their duty!! Normally these faults would clear upon battery disconnect/reconnect, but reappear within 10-15 mins.
This particular SAM is a pig to take apart, and if you are contemplating inspecting your own - be prepared for some plastic casing surgery or be comfortable with the thought you may have to buy a replacement should things go wrong. THEY ARE A PIG TO REASSEMBLE.

Time will tell if this has been the root cause of my problems - a popped 70p capacitor!!!