In a system for assisting the regeneration of depollution apparatus associated with an oxidation catalyst implementing an OSC function, constituting a supply of oxygen and integrated in an exhaust line of a motor vehicle diesel engine, in which the engine is associated with a common rail for feeding its cylinders with fuel, the running conditions of the vehicle are analyzed and compared with predetermined threshold values, to control the engine in a first regeneration mode of operation with a lean mixture when running conditions are above the threshold values, or in a second regeneration operating mode implementing sequences in which engine operation alternates between stages of rich mixture operation and of lean mixture operation when conditions are below the threshold values.