In the method of diagnosing the operating state of a motor vehicle diesel engine of the invention, the engine includes a pressure acquisition system associated with each cylinder of the engine to acquire the pressure in that cylinder, an engine shaft angle acquisition system adapted to deliver the crankshaft angle of each cylinder, and onboard correction system adapted to correct a predetermined set of malfunctions and drifts of the cylinders and the acquisition systems. The method includes an analysis step of analyzing the operation of each cylinder and the cylinder pressure and engine shaft angle acquisition systems by identifying an operating state of the set comprising that cylinder and those systems based on predetermined characteristics of the signal delivered by the cylinder pressure acquisition system, and a correction step of correcting identified malfunctions and drifts.