The results of experimental studies of the rolling stock traction electric motors collector profile are presented. A technique is shown for combining collector’s profilograms in the cold and hot state for non-synchronized values of the origin. A new diagnostic parameter is proposed for assessing the state of the traction electric motors collector profile - the root-mean-square value of the difference in the relative heights of the collector plates in cold and hot states. The changes comparison results in the proposed diagnostic parameter for traction electric motors after repair in a locomotive repair depot are presented. The analysis of the influence of the collector formation on the state of the rolling stock traction electric motors collector profile is carried out. It is shown, that the change in the collector profile can be caused by two reasons - poor-quality forming, as well as poor-quality repairs.