A method for timing performance of a maintenance function, in particular the timing of regeneration of a diesel particulate filter (22) to conserve fuel as a motor vehicle (10) travels along a projected travel route. Certain road data about roads in a roadway system is processed to develop data for anticipating certain modes of vehicle operation during travel of the vehicle along the projected travel route. The data for anticipating certain modes of vehicle operation along the anticipated route of travel and data geographically tracking vehicle travel along the projected route are interactively used to control timing of performance of the maintenance function as the vehicle travels along the projected route.