The scrurity system keeps shutting the engine down.

What is your question?

This is an Airporter bus, 27 passenger. We have had it run for long periods of time, then for some unknown reason, it will shut down by the security system. This has happened several times and we hqave had 2 mechanics work on it and cannot find out the problem. We had it to a Chevy dealer in Juneau, Alaska and all they did was give us the procedure to reset it if it happens. We operate a tour company in Haines, Alaska and cannot use the bus because we cannot trust it. It is unacceptable to simply go through a procedure to reset it, if it shuts down because we would have passengers in the bus and it is a very uncomfortable feeling for them and embarrasing for our driver. Please help me. We can't even sell the bus with this issue.