A simple one-dimensional model for a three-way catalytic converter is briefly described and solved. It accounts for the HC(hydrocarbons)/CO oxidation and NO reduction reactions. The engine experiments include temperature, air/fuel ratio and gas flow step changes and pulses. In spite of the numerous simplifying assumptions, the agreement is good. The discrepancies are essentially attributed to the accuracy limit of the time-resolved input data, to the extreme sensitivity of the reactions about light-off temperature, to a possible internal diffusion limitation at high temperature, and to some transient state catalytic process which was neglected in the model. Thermal shocks only validate the thermal description of the model. Slow temperature excursions about light-off, and changes of the air/fuel ratio are more conclusive for the chemical description. The study of high-frequency signals requires an efficient data correction procedure and probably to include a description of oxygen storage into the model.