A method for establishing a maintenance diagnosis on an engine, the engine comprising a throttle which regulates air access into an air intake system of said engine, a position sensor which measures the position of the throttle, a manifold in fluidic communication with the throttle, a pressure sensor which measures the pressure in the manifold, at least one intake valve, a richness probe which measures an oxygen level and a richness controller for modifying the proportions of air and fuel in the air-fuel mixture, the method including a first set of steps implemented at the end of the production line for the engine or following maintenance of said engine, the first set of steps comprising the following steps:
- ignition of the engine, and when the engine is in predetermined conditions,
- - determination of a first air flow dbTPS in the air intake system from the position VTPS_mesure of the throttle measured by the position sensor,
- - determination of a second air flow dbp in the air intake system from the pressure Pmesure in the manifold measured by the pressure sensor,
- determination of a reference measurement correction factor, selected such that when the reference measurement correction factor is added to the measurement of one of the two air flows in the determination of a third corrected air flow dbcor based on the same calculation as said one of the two air flows dbp or dbTPS, the third corrected air flow dbcor is substantially equal to the other said one of the two flows,
- correction of a theoretical injection command Cinj of the richness controller, determined from one of the two air flows dbTPS or dbp, by the addition of a reference injection correction factor so as to obtain a substantially stoichiometric air-fuel mixture on the basis of measurements from the richness probe, and
- after at least one determined duration during which the steps of determination of the first air flow dbTPS, determination of the second air flow, determination of the reference measurement correction factor and correction are performed several times,
- storage of the reference measurement correction factor and the reference injection correction factor,
- the method comprising a second set of steps implemented during conventional operation of the engine and when the engine is in said predetermined conditions,
- the second set of steps comprising the following steps:
- determination of a first air flow db′TPS in the air intake system from a position V′TPS_mesure of the throttle measured by the position sensor,
- determination of a second air flow db′p in the air intake system from a pressure P′mesure in the manifold measured by the pressure sensor,
- determination of a current measurement correction factor, selected such that when the current measurement correction factor is added to the measurement of said corresponding one of the two air flows db′TPS or db′p in the determination of a third corrected air flow db′cor based on the same calculation as said one of the two air flows db′TPS or db′p, the third corrected air flow db′cor is substantially equal to the other said one of the two flows db′TPS or db′p,
- correction of an injection command C′inj of the richness controller determined from the corresponding air flow by the addition of a current injection correction factor so as to obtain a substantially stoichiometric air-fuel mixture on the basis of measurements from the richness probe, and
- when the absolute value of the difference between the reference measurement correction factor and the current measurement correction factor is greater than a determined threshold,
- establishment of a maintenance diagnosis,
- calculation of an absolute value of the difference between the reference injection correction factor and the current injection correction factor, and:
- 1) when the absolute value is less than a determined threshold ΔLcL,
- if the injection command C′inj is determined from the first air flow db′TPS obtained from the position of the throttle, establishment of a diagnosis of a play at the at least one intake valve, and
- if the injection command C′inj is determined from the second air flow db′p obtained from the manifold pressure, establishment of a diagnosis of clogging of the throttle, or
- 2) when the value is greater than said determined threshold ΔLcL,
- if the injection command C′inj is determined from the first air flow db′TPS obtained from the position of the throttle, establishment of a diagnosis of clogging of the throttle, and
- if the injection command C′inj is determined from the second air flow db′p obtained from the manifold pressure, establishment of a diagnosis of a play at the at least one intake valve .