The invention relates to idler diagnosis systems on conveyors, comprising a rail system as a track for suitable running gears and the running gear, the rail system being formed from a closed profile or tube. The rail system comprises a multi-part track holder arranged on the belt frame, a fixing rod and a running rail, the track holder being suitable for accommodating the running rail at at least one end by insertion, thus creating a track without cross-section differences. The running gear has at least one two-roller system as a guide and drive system, and at least one chassis that accommodates and connects the two roller systems and has connection options for sensor-system carriers and/or energy control module. The guide system encloses the track so only one movement (forwards/backwards) along the track is provided. The drive system moves the chassis and all the connected systems with respect to the track.