Engine Shut Off Without Warning problems of the 2009 Mercury Mariner

My 2009 Mercury Mariner (has 56,000 miles), without any warning, it just shut off while I was driving it. Has happened twice. Was able to get the side of the road and was able to restart it. No warning lights came on at all. Car is at dealership now to have it checked out.

10/12/13 - traveling on highway with the cruise control set at 70mph the engine just shut off. I coasted to the side of the road, put it in park, waited a minute or two, then started the car. It ran without incident for 20 minutes until I reached home. 10/15/13 traveling on highway 60mph the engine just shut off. I shifted into neutral and tried to start it, but it would not respond. I coasted across two lanes of traffic to the side of the road, put it in park, waited a minute or two, then started the car. It ran without incident for 20 minutes until I reached home. 10/17/13 Ford dealership could not find anything wrong with the vehicle. Nothing in the codes. Replaced the relay switch 10/18/13 traveling on market street in youngstown, ohio at a speed of 30mph the engine shut off. I coasted in to the center turn lane, put it in park, waited a minute and started the car. The vehicle is riding more rough and sputters now and then. Drove for 10 minutes in city traffic without incident 10/18/13 while driving 45mph in rural area the engine shut off. I pulled to the side of the road, put the car in park and started the engine. This was the first time I notice a yellow wrench light on in the lower left portion of my dashboard. Car rides rough and sputters a bit. After all these multiple incidents in a short period of time I refuse to drive the car. It is not safe to drive and is not dependable. The engine shuts off without warning at all speeds, but on the highway without warning is unacceptable.