Go into the menu on the right hand stacks on the truck and see if there is any faults showing , for some more info ,if not it will be a plug in job to see what’s bothering it ,it could be anything ad blue fault to a double vale on passenger side of the engine behind the chassis with pipes running to drivers side ,that they have a habit of doing in , for the long life of me I can’t remember the name of but they are around £500 quid and are a pain to fit , these Bring on stop sign and reduce power , but without more info could be anything or nothing by tomorrow