Abstract: A method for the diagnosis of an exhaust gas purification system for an internal combustion engine, provided with a pre-catalyst and a main catalyst disposed along an exhaust duct of an internal combustion engine; the method including the stages of determining a real heat supplied to the exhaust gases in the pre-catalyst as a function of a input temperature and an output temperature of the exhaust gases at the input and output respectively of the pre-catalyst; determining a nominal heat supplied during nominal operating conditions of the pre-catalyst; calculating an index representative of the state of wear of the pre-catalyst, as a function of the real heat and the nominal heat; comparing the index with a threshold value.

Abstract: A self-adapting control method for an exhaust system for internal combustion engines with controlled ignition, including an engine, a pre-catalyst, a trap for the collection of nitrogen oxides having a maximum initial capacity and a maximum available capacity not greater than this maximum initial capacity and a linear oxygen sensor disposed downstream of the trap for the collection of nitrogen oxides and generating at least a downstream composition signal substantially proportional to a downstream oxygen titer. The method comprises the stages of carrying out at least one regeneration process and carrying out at least one desulphurisation process of the trap for the collection of nitrogen oxides and also the stage of estimating, at least after each regeneration process, the maximum available capacity as a function of the maximum initial capacity and the downstream composition signal.