I modded it to gear down the extruder 2.5:1. The UM 2+ has geared down extruder, since the UM2 extruder was underpowered and slipped. The failure mode is stalling, which is normal for a bowden printer of any quality -- if there's obstruction farther down, you'll hear the motor go clack-clack. Just stop it, hand feed the filment back and forth to "feel" for where it's catching.
Usually it's just that the filament got too melty & thick at the end due to bad retraction settings and catches on the hotend. Rule of thumb for ultimaker retraction settings:
diameter of nozzle * 10 or a little less.
So, with a .4mm nozzle, 3-4mm retraction is about right.
L