Abstract: A leak diagnosis apparatus and method for a fuel vapor treatment unit where fuel vapor produced in a fuel tank is collected by adsorbing into an adsorption canister and the fuel vapor collected in the adsorption canister is purged under predetermined engine operating conditions and supplied to an engine. The diagnosis apparatus includes a leak diagnosis device unit for diagnosing the presence of fuel vapor leaks by comparing a drive load of an electric pump for when air is pumped by the electric pump into a system of fuel piping to be leak diagnosed with a set judgement level of drive load threshold. A fuel temperature detection device is provided for detecting the temperature of fuel, wherein a fuel vapor leak is deemed to exist when the comparisons show that the drive load of the electric pump is less than the set judgement level. A judgement level setting device is provided for setting the judgment level based on the detected temperature.

Abstract: With a fuel vapor treatment unit where fuel vapor of an internal combustion engine which has been temporarily adsorbed into an adsorption device is drawn into an engine intake system under predetermined engine operating conditions, a judgment level is set based on a drive current of an electric pump for when air is pumped by the electric pump via a reference orifice having a reference aperture diameter, and the presence of fuel vapor leakage is diagnosed by comparing a drive current of the electric pump for when air is pumped by the electric pump bypassing the reference orifice and into piping to be leak diagnosed of the fuel vapor treatment unit, with the set judgment level. Moreover, the drive current of the electric pump for when air is pumped via the reference orifice is compared with a reference level, and when the drive current deviates from the reference level, the leakage diagnosis is stopped.