RATIONALITY DIAGNOSTIC DEVICE FOR ALCOHOL CONCENTRATION SENSORS

An object of the present invention is to properly and easily diagnose the rationality of an alcohol concentration sensor that measures the alcohol concentration of fuel used in an internal combustion engine. To achieve the above object, a rationality diagnostic device for an alcohol concentration sensor, which is provided by the present invention, includes a capacitance-type remaining fuel amount sensor as a remaining fuel amount sensor disposed in a fuel tank. The capacitance-type remaining fuel amount sensor has such output characteristics that its output value is determined by the amount of fuel remaining in the fuel tank and the alcohol concentration of the fuel. The rationality diagnostic device corrects the output value of the remaining fuel amount sensor in accordance with the output value of the alcohol concentration sensor to eliminate an alcohol-concentration-dependent component from the output value of the remaining fuel amount sensor. The rationality diagnostic device then verifies the accuracy of the corrected output value of the remaining fuel amount sensor to judge whether the rationality of the alcohol concentration sensor is maintained.