So I was coasting in the Class 66 about 1.6 miles west of Hoo Jct on the 6Y08, getting ready for the upcoming approach control for the siding. Out of nowhere, I get the message "The engine has unexpectedly shutdown." I was able to cold start and drive away, completing the service. Since others have had similar experiences, I was wondering if this is a feature or a bug? I really don't think it was anything I did, because I was just coasting and not manipulating anything at all. If I had managed to get these grain loads up and over from Dartford without breaking anything, I don't think I could have screwed anything up by doing nothing. And, in my hundreds of hours driving in TSW, I have never seen this message. If it is a bug, that's too bad. This was a pretty cool experience.
https://forums.dovetailgames.com/threads/random-event-class-66-engine-shutdown.58229/ You are not alone
On the linked thread above, Matt replies to say that it is a bug and isn’t supposed to happen. I certainly enjoyed the experience when it happened to me as I thought it was genuinely replicating a fault but it appears that it is just a bug.