I am trying to pass an object to another scene with prepareForSegue()
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObj
What that error is telling you is that segue.destinationViewController isn't a VehicleDetailsTableViewController. We don't have enough details to tell you why.
Check your segues and make sure they're all pointing to the correct place, and always check the identifier of your segue before you perform a cast.
if segue.identifier == "theNameOfYourSegue" // then do your cast