Vehicle air-conditioning system

A fuel injection control unit for an internal combustion engine, which is suitable for failure diagnostics of a pressure sensor of a cab air conditioner. A fuel injection control unit for an internal combustion engine (12), which is employed for controlling fuel injection of the internal combustion engine and also for controlling a cab air conditioner (10), characterized in that when an input value from a pressure sensor (11) for detecting the coolant pressure of the cab air conditioner (10) does not change to the outside of a range of preset values even if a preset time elapses since a control switch of the cab air conditioner (10) has been switched from OFF to ON, a decision is made that a line of the pressure sensor (11) has been disconnected.