Smartcarsubi we had a similar problem.
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Our smart would drop out of cruise and then throw an error message. The headlights would act up when you tried to switch from low to high and then not switch back. The steering column would not release the key.
We took it two a couple of different smart dealers in different states because we travel, with no diagnosis. So we ended up taking it back to the dealer we got it from. When we pulled up to the service area, the key would not come out. The dealer after about a week replaced the car battery and the SAM unit. Simply put the SAM unit is the analog interface for everything in the car to the computer.
Months later while driving from Houston to Galveston we were 10 ' from our parking spot when the car started acting anything but smart. The engine was running but every alarm and idiot light possible came on. The radio kept coming on and off, the headlights started flashing and I swore our car was possessed. The transmission just showed 3 lines so I turned it off to clear the error messages, but this time it would not restart.
Within a few days we had it towed to the Mercedes Benz dealer in North Houston. I showed them the video and discussed our service history with the service writer. A couple of days later we received the attached photo from the service tech that showed the wiring harness on the drivers side near the wheel well had been arching against the frame. The service tech ordered a new harness and while he was waiting for it to come in, he inspected a few other newer generation smarts and found they were beginning to have the same issue we had. Their wiring harnesses were starting to wear.
They replaced our harness and secured it to the frame and since then we have had no other problems. I do not know if this is the same problem you are having. It sure is manifesting itself with some of the same symptoms we had over a few years.
