Cruise control function: General

Cruise control is operated with a switch on the direction indicator stalk. The switch (141) is an integrated part of CIM (703), which sends the position of the switch as bus messages.

Fig 1: Switch And CIM - Communication Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

ECM uses these bus messages for the cruise control function. When the switch is moved to "ON", the cruise indicator lamp in MIU will come on. When the "SET" button is pressed, ECM will store the current vehicle speed in its memory. This is provided all the conditions for activating cruise control have been met.

Fig 2: ECM, P-BUS - Communication Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

ECM then reads from a table containing the nominal rolling resistance on a flat surface at different vehicle speeds. This results in an engine torque request to maintain a constant speed.