NH3 slip detection using NOx sensor

A system comprising:

• an exhaust aftertreatment system comprising a catalyst, and a system-out NOx sensor disposed downstream of the catalyst;
• and
• a controller configured to:
• access a temperature value for the catalyst;
• when the temperature value for the catalyst exceeds a predetermined temperature value and one or more first prerequisite conditions are met:
• access a plurality of system-out NOx measurement signals from the system-out NOx sensor,
• determine a plurality of estimated system-out NOx values,
• calculate a plurality of delta values over a first predetermined period of time, based on the system-out NOx measurement signals and the estimated system-out NOx values, and
• set a flag indicative of NH3 slip for an exhaust system responsive to an average of the plurality delta values exceeding a first predetermined value;
• and
• when the temperature value for the catalyst is below the predetermined temperature value and one or more second prerequisite conditions are met:
• access a plurality of system-out NOx measurement signals over a second predetermined period of time,
• calculate an average of the plurality of system-out NOx measurement signals, and
• set the flag indicative of NH3 slip for the exhaust system responsive to the calculated average of the plurality of system-out NOx measurement signals exceeding a second predetermined value.