A method is disclosed for operating an automotive system having an internal combustion engine equipped with an exhaust gas aftertreatment system including a Lean NOx Trap (LNT) upstream of a Selective Catalytic Reduction washcoated particulate filter (SCRF). A LNT inlet temperature is monitored. A parameter representative of a quantity of NOx stored in the LNT is also monitored. A map correlating the LNT inlet temperature and the quantity of NOx stored in the LNT is used to estimate an ammonia quantity produced during a LNT regeneration. A LNT regeneration is performed, if the estimated ammonia quantity is greater than a threshold value thereof.