Failure diagnosis apparatus for fuel level sensor and failure diagnosis method for fuel level sensor

A failure diagnosis apparatus for a fuel level sensor that detects a fuel remaining quantity within a fuel tank including at least a first tank and a second tank includes: a range deter mining unit for determining a range of a fuel remaining quantity on the basis of an output value of the fuel level sensor, the range being classified into a plurality of ranges in accordance with an output characteristic of the fuel level sensor; and a range failure diagnosis unit for carrying out failure diagnosis of the fuel level sensor for each range by comparing a fuel consumption quantity since the ranges are changed with a failure determining threshold value individually set up for each range. In a dead zone range in which a change in the output value of the fuel level sensor becomes small when a fuel consumer is switched from the first tank to the second tank, the range failure diagnosis unit sets the failure determining threshold value to a value corresponding to a fuel consumption quantity required to pass through the dead zone range.