New Flyer Industries Ltd. (New Flyer) is recalling certain model year 2013 XD40 buses manufactured May 24, 2013, through September 5, 2013; model year 2013 XN40 buses manufactured April 18, 2013, through September 11, 2013; model year 2013 XD60 buses manufactured May 31, 2013, through September 5, 2013; and model year 2013 XDE40 buses manufactured on May 17, 2013. The color coded air lines to the E-6 brake treadle valve may have been installed incorrectly. Thus, these vehicles fail to conform to the requirements of Federal Motor Vehicle Safety Standard No. 121, “Air Brake Systems.”