A selective catalytic reduction (SCR) device monitoring system includes an engine out NOx monitoring module, an SCR out NOx monitoring module configured and disposed to monitor NOx released from the SCR device, and a NOx storage model module operatively connected to the engine out NOx module and the SCR out NOx monitoring module. The NOx storage model module is configured and disposed to determine an amount of NOx stored in the SCR device. A consumed ammonia correction model module is operatively coupled to the NOx storage model module and configured and disposed to calculate a corrected consumed ammonia correction factor.