Method and system for controlling a drivetrain retarder

A method of operating a retarder control system for a drivetrain retarder such as an engine compression brake of a heavy-duty truck vehicle is disclosed. The method of operation includes three novel subsets each of which controls the operational state and the resistance level at which the drivetrain retarder is operated dependent at least partially upon one or more factors including speeds of one or more drivetrain components, vehicle speed, rotational speed of one or more undriven wheels, position of a brake control member, elapsed time of activation of a brake control member and/or elapsed time from a change in a selected resistance level at which the retarder control system is commanded to effect operation of the drivetrain retarder.