To detect a failure of the fuel heaters of a multi-cylinder internal combustion engine of vehicles by utilizing a microcomputer of a vehicle operation control device and sensors already provided in the vehicle such as an air/fuel ratio sensor or a crankshaft rotation sensor, with a supplement of substantially only a software, a failure of the heater corresponding to one of the cylinders is detected based upon a change exhibited in at least one parameter with regard to the operating conditions of the engine such as exhaust air/fuel ratio, crankshaft rotation angular speed, etc. by the injected fuel not having been heated as expected by a predetermined operation of each heater.