System for checking a combustion engine (1) coupled with an electric generator (2) of a hybrid terrestrial vehicle having at least a drive line (61, 62) driven by at least one electric motor (51, 52); the combustion engine (1) comprising at least one subsystem to be checked; the system further comprising first control means (3) configured to drive the combustion engine (1) at a predefined deterministic operation point, wherein the system comprises second control means able to perform a diagnostic test on the subsystem wherein the first control means (3) are configured to vary the operation conditions of the combustion engine (1) in order to allow the second control means (ECU) to perform the diagnostic test.