Last night I was driving my 2009 Smart Passion on a busy 40 MPH highway and while I was coming up to a stop light, I started to use the break and it first seemed like the brake was failing, and then the whole car shut of like it seemed to shut off like someone turned the ignition off. Luckily the brake sort of worked so I did not hit the person in front of me, but I was almost hit from behind. I had to put on my E brake and flashers and get someone to help me stop traffic (I was in the left lane) and someone else to help push my Smart off the road. 

It was not the battery because I could still turn the ignition key and get all headlights, radio and air (except AC). I just couldn't get the car to turn over and all the dash lights (check engine, oil, ect) came on.

I got it towed to Mercedes in Seattle and they said today that the main computer that runs the car had completely died. They needed to replace it. They were not sure why this had happened and supposedly had never seen anything like this before. I requested they look into the computer box when they pull it out to see what had happened. I have a job where I have to be at work on time, I commute, and the Smart is my only car. I had just had my car in for it's 80,000 mile check up in April. Now this is a major $1500 expense.

If I had been on the freeway, or had been going any faster, this could have caused a major accident.

Has anyone else experienced this or heard of just a thing happening?

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First, you can report this to the NHTSA as a safety issue:

Not the only instance of this; several have been documented on SCoA.  "Main computer" could mean the SAM (under the dash) or the ECU (right rear behind the cargo area trim.)  The dealer needs to be more specific. Some SAMs have failed due to water leaking into them; in Seattle that could be the issue (if it is the SAM.)

There's a company in Oregon that may be able to help you:

Wow! We are so glad you are OK! Could you please inbox us your email address and phone number? We would like to put you in touch with customer care to ensure that this problem is addressed in full. 

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