After treatment system for a variable displacement engine

A method (100) and system (10) for controlling the temperature of a first NOx trap in an aftertreatment system for a variable displacement engine (12). The frequency of switching between first and second cylinder banks (14, 16) of said variable displacement engine (12) controls the temperature of the NOx trap (18) in order to maintain the temperature within a preferred operating temperature range. A set of control valves (V1, V2, V3) is used to direct the flow of exhaust from alternate cylinder banks (14, 16) through various paths in order to maintain the desired temperature of the first NOx trap (18). In another embodiment (30), the aftertreatment and method (120) include a second NOx trap (26) for situations in which both engine banks (14, 16) are run simultaneously.