PURPOSE: To allow a vehicle to limp off a road to a safe place nearby by, when sensing conditions of a system fault that shifting of a main section in a transmission cannot be performed, retaining the main section engaged in a selected ratio while issuing command output signals for causing shifting of only an auxiliary section.

CONSTITUTION: An automated mechanical transmission system 12 comprises a compound mechanical transmission 14 comprising a multiple ratio main section connected in series with a multiple ratio auxiliary section, a fuel controlled engine 16, a nonpositive coupling 10 interposed the engine and the transmission. Further, a central control unit 50 logically processes detected signals from a plurality of system sensors 36, 42, 44, 28 so as to control a plurality of system actuators 40, 28, 48, respectively. In this case, during shift control, the presence of conditions indicative of a system fault undesirably rendering continuing main section shifting in the transmission 14 is sensed, and in response to the conditions of the system fault, the main section is engaged in a selected ratio. Further, the state of the main section engaged in the selected ratio is maintained while issuing command output signals for causing shifting of only the auxiliary section.