A control system for a vehicle includes a CPU, a throttle sensor, a shift actuator, and fuel injectors. When the CPU detects a control failure of the throttle valve with a value detected by the throttle sensor, the CPU adjusts the output of the engine by controlling the fuel injectors such that the motorcycle runs with a previously set negative target acceleration. Also, the CPU controls the shift actuator such that the transmission is shifted down in steps as the speed of the motorcycle decreases.