A method for diagnosing the operation of an injector of a diesel engine of a vehicle, controlled by a plurality of control laws on the basis of at least one operating parameter of the injector for each control law. The method includes a step of measuring an operating parameter value during use of the injector, a step of determining an efficiency value of each control law on the basis of the measured value of the parameter and of a predetermined reference curve representing the efficiency of the parameter in its interval of operating values, and a step of determining an efficiency value of the injector on the basis of the efficiency value of each of the control laws.