Abnormality determination method for purge system and abnormality determination system for purge system

An abnormality determination method for a purge system, the purge system including a vapor passage connected to a fuel tank, a canister configured to collect vaporized fuel transmitted from the fuel tank through the vapor passage, a purge passage including a purge pump that supplies the vaporized fuel absorbed in the canister to an internal combustion engine, and an outside air introduction passage allowing the canister to communicate with outside air and to which an outside air shutoff valve is attached, the abnormality determination method being for determining an abnormality in the vapor passage or the purge passage in the purge system, the abnormality determination method comprising:

• determining a first value of a physical quantity by closing the outside air shutoff valve while the purge pump is driven at a first speed,
• classifying the physical parameter into a first range in which it is determined that there is no abnormality in the vapor passage and the purge passage or a second range in which it is determined that there is a possibility of an abnormality in the vapor passage or the purge passage, with a first threshold value as a boundary between the first range and the second range;
• opening the outside air shutoff valve,
• when the physical parameter is in the second range, determining a second value of the physical quantity by closing the outside air shutoff valve while the purge pump is driven at a second speed higher than the first speed;
• classifying the second value into a third range in which it is determined that there is no abnormality in the vapor passage and the purge passage or a fourth range in which it is determined that there is an abnormality in the vapor passage or the purge passage, with a second threshold value as a boundary between the third range and the fourth range;
• and
• determining that there is a clog in the vapor passage or the purge passage when the second value is in the fourth range.