This paper deals with the NAVI-5 system which has been used on Isuzu ASKA passenger cars since 1984 and which has now been introduced on light-duty trucks, NAVI-5 is a total power train control system which is in fact a package of conventional manual transmission, dry clutch and engine output control. All of these package components are controlled automatically by a microcomputer and electronically-controlled actuators to function in unison. The system has a diversity of functions such as automatic gear selection, automatic clutch, cruise control and engine idle speed control.The cruise control function is especially noteworthy. On trucks, vehicle running resistance varies much more widely than on passenger cars because of varying cargo weights, and this is why maintenance of constant speeds by electronical control has been very difficult with conventional systems. NAVI-5, however, incorporates a simple means of determining the running resistance and thereby controlling engine output and transmission gears to obtain optimum performance.The outline of NAVI-5 and the control logic of the cruise control are explained in this paper.