Method for controlling and/or monitoring the performance of selective catalytic reduction devices (SCR) and systems incorporating the same are provided. Systems can include a SCR configured to receive reductant at a variable dosing rate, an upstream NOx sensor, and a downstream NOx sensor. Methods can include correlating a SCR reductant dosing signal direction with a SCR downstream NOx signal direction, and determining one or more of NOx breakthrough through the SCR and reductant slip through the SCR. Methods can further comprise identifying reductant slip through the SCR using an upstream NOx sensor signal and a downstream NOx sensor signal. Methods can further comprise comparing an upstream NOx signal to a downstream NOx signal, determining a system objective, and adapting the SCR reductant dosing rate to achieve the system objective in order to identify a faulty upstream NOx sensor.