The invention relates to a method for correcting a model (M) for estimating a quantity of NOx upstream of a catalytic reduction system (51) for a heat engine (2) adapted to inject a NOx reducer, characterized in that it comprises the following steps: - apply a first correction strategy (Strat_corr_1) by applying a first correction coefficient to the quantity of reducer to be injected, - detect an overestimation or underestimation judged unacceptable of the quantity of NOx by the model (M), - if such detection is confirmed, apply a second correction strategy (Strat_corr_2) in which the estimation of the quantity of NOx of the model (M) is corrected by a second coefficient for correcting the quantity of NOx applied to the model (M).
