This work analysis the causes and presents solutions for the non-uniform distribution of the flow in an automotive catalytic. The catalytic converters are usually installed in the exhaust pipe of the vehicle, with a diffuser connect ivy housing of the monolithic ceramic. The diffusers currently used do not provide a good performance, because of their high area ratio (A > 3) and large divergence angle (2θ > 10°). Due to boundary layer separation on the walls of the diffuser, the flow occurs in the form of a “jet”, with high speeds at the center. The non-uniform distribution of the flow causes an irregular use of the catalytic area. The results are an increase in the production costs, in the pressure drop and in the time to “light-off”. In this work, the non-uniformity of the flow was measured with a Pitot tube, in an experimental rig specially designed for this purpose. The insertion of screens in the diffuser perpendicular to the flow can reduce the adverse gradient of pressure, avoiding the separation of the boundary layer. The screens were tested to find the correct mesh and the ideal position in the diffuser. One or more screens can be used, depending on the level of uniformity required. The experiments showed that this method of flow control is capable of producing a uniform velocity profile. If was also found that the method does not significantly affect the total head loss in the catalytic converter.