My Nissan Xtrail keeps on braking outomatically without warning what could be the issue.

Hello, if you have a vehicle of this vintage that appears to have brakes applied, I'd be concerned about some kind of anti-lock brake system activation for some reason. But I'd expect warning lights to be on if this happened, so I would say it's unlikely that your mechanical braking system is doing anything. I'd say it's more likely you have an engine performance or transmission engagement issue that could be causing some troubles. Either way, it's best to have a technician near you evaluate what you are experiencing first hand, utilizing test equipment and experience to figure out what direction to go into. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops