A method is disclosed for operating an automotive system having an internal combustion engine equipped with an exhaust gas aftertreatment system including a Lean NO.sub.x 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 NO.sub.x stored in the LNT is also monitored. A map correlating the LNT inlet temperature and the quantity of NO.sub.x 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.

Systems and methods for diagnosing at least one component in an exhaust aftertreatment system are provided. The system includes an exhaust aftertreatment system coupled to an engine system, at least one sensor, and at least one processing circuit structured to: receive initial sensor data; determine an initial parameter value based on the initial sensor data; determine that the initial parameter does not satisfy an initial threshold; perform operations to diagnose at least one component of the exhaust aftertreatment system comprising: causing the engine system to operate through a sequence of a plurality of engine outputs; receiving a plurality of sensor data, each of the plurality sensor data corresponding to at least one of the plurality of engine outputs; comparing each of the plurality of sensor data to a corresponding threshold; and diagnosing the at least one component based on the comparison.