Spatially 1D simulations of exhaust gas catalysts are often used in the automotive industry because of short computation times. In fully 3D CFD-based model, the computational requirements increase by several orders of magnitude. A novel approach to 3D simulations of complete exhaust gas aftertreatment systems is proposed in this paper. It is based on a modular combination of standard CFD tool with a user-defined 1D channel model. The employment of external 1D channel model enables more effective computations and gives maximum freedom in definition of realistic reaction kinetics, including non-linear rate laws and fully transient solution of adsorbed components. The approach is validated by comparison of the results from the stand-alone 1D model and single channel CFD simulation. Dynamic simulations of CO oxidation light-off and lean/rich operation of NOx storage catalyst (NSRC, LNT) are then conducted in a test geometry with 10 representative channels and skewed inlet/outlet pipes. Finally, a complex system including bent pipes and conical expansion/constriction parts is simulated with 80 representative channels. It is demonstrated that relatively large deviations can exist between the individual channels. Non-uniform inlet flow distribution affects light-off behaviour as well as breakthrough of adsorbed components, and it may also lead to a different extent of catalyst ageing in individual channels. The combined 3D CFD and 1D channels simulation approach represents an effective tool for analysis of such problems and can help with the design of more efficient exhaust gas aftertreatment systems. (C) 2012 Elsevier B.V. All rights reserved.