No crank start error DAS ECU fault - SLK R170 Restoration Video 13

One day my SalK project car stopped cranking. Nothing at all changed on key position 3. No click, nada.
The message “start error” did not display.
I checked out the notorious K40 relay and found it to be in good shape and working normally.
The transmission was reporting correctly, the SRS system had a fault but was an unlikely cause, and I changed the crankshaft sensor, because it was a possible suspect.
This video shows the root cause being finally found, after several weeks of head scratching.

[@mancykall7394]

gracias buen trabajo, mi slk 230 año 1999 no arranca revisare la ECU y la cambiare, espero me resulte.

[@SteveWardellDIY]

Good luck, and thank you for watching.

[@bronfoo1582]

I can definitely see how much you were enjoying that moment with engine sound!! As the owner of same car, 22 - years - old slk230 449, it dosen't feel like someone else's business!! When I saw your last vidoe examining k40 I thought it must be a cause! How happy must you have been when you finally found the cause after such a long journey!! How you could be sure that k40 relay was all fine, though? In your video, traction control relay, eng. control relay and fuel pump relay were on at ign1 and then fuel pump relay was off at ign2. Was that a proof that k40 was okay?

[@SteveWardellDIY]

Good question. The logical sequence of the K40 isn’t known to me, but having scrutinised it carefully with test lamps, multimeters and my eyes, and reflowing solder joints just in case, I do know I have confidence it’s in good shape.
I received my old DAS and ECU back from a specialist. They found it failed several times on their test bench then is started working okay. Comms between the two seemed to be the problem. They reflowed the DAS for me, and they said it didn’t fail again.
At some point I’ll refit it but it’s been running fine since the video on the replacement.
Thanks for watching.