Error diagnosis device and error diagnosis method

A malfunction diagnosis device for diagnosing a malfunction of a fuel pump that includes a flow control valve for adjusting a flow rate of fuel pumped up from a storage section, and a high pressure pump for pressurizing the fuel whose flow rate is adjusted and discharging the fuel to a pressure accumulator section, the malfunction diagnosis device comprising:

• an input section that receives a detected value of a pressure of the fuel in the pressure accumulator section;
• a calculation section that calculates, when the detected value is less than a target value of the pressure, a differential pressure between the target value and the detected value, and a discharge amount of the fuel discharged from the fuel pump;
• and
• a determination section that determines whether a preset time has passed in a state where the differential pressure is equal to or more than a first threshold value and less than a second threshold value while the discharge amount is equal to or more than a third threshold value and less than a fourth threshold value,
• wherein the determination section determines that:
• a malfunction has occurred at the high pressure pump, when the preset time passes, and
• a malfunction has occurred at the flow control valve, when the preset time does not pass, and
• wherein the first threshold value is an upper limit value of the differential pressure when all of plungers provided in the high pressure pump operate normally;
• the second threshold value is an upper limit value of the differential pressure when at least one of the plungers operates normally and at least one of the plungers is broken;
• the third threshold value is a lower limit of a maximum dischargeable amount of the high pressure pump when at least one of the plungers operates normally and at least one of the plungers is broken;
• and
• the fourth threshold value is a lower limit of a maximum dischargeable amount of the high pressure pump when all of the plungers operate normally.