Method and unit for diagnosing leakage of an internal combustion engine high-pressure injection system

The diagnostic method includes the steps of: generating a pressure signal (SP) related to the fuel pressure of an injection system (1) of an engine (2); comparing the pressure signal (SP) with a reference pressure value (PO); determining a fuel leakage condition of the injection system (1) when the pressure signal (SP) is less than the reference pressure value (PO); reducing the quantity of fuel injected into the cylinders (3) of the engine (2) in the presence of the leakage condition; calculating a share value (CI,i) contributed by each cylinder (3) to the work torque value (CU) generated by the engine (2); comparing each share value (CI,i) with a respective reference share value (CO,i); determining a jammed-open injector condition when at least one of the share values (CI,i) is greater than the respective reference share value (CO,i); and determining a supply circuit failure condition when the share values (CI,i) are all less than the respective reference share values (CO,i).