Automatic Grade Braking – How does it work?
A. The grade-braking feature’s primary purpose is to utilize engine braking to slow a heavy vehicle on steep grades in order to reduce wear on the traditional braking system. The method used to slow the vehicle is by overriding the PRNDL position, effectively pre-selecting the next lower gear range automatically. Because the transmission is electronically controlled and there is no mechanical linkage that needs to be moved for a pre-select downshift, implementation of this feature can be done completely in software with no hardware modifications. This control feature takes into consideration several factors before commanding a pre-select downshift. These are the primary inputs to the Transmission Control Module (TCM): • Throttle position • (Service) Brake state • Vehicle acceleration/deceleration • Grade/Load • Vehicle speed These factors are continually calculated to determine when a preselect downshift is commanded.
