System and method for estimating engine exhaust nitrogen oxide sensor instability

A system and method is provided for estimating engine exhaust nitrogen oxide sensor signal instability in transient conditions, for example when rapid changes occur in driver demanded torque, and for eliminating fluctuations in EONOx sensor signal status, in order to have more robust on-board diagnostics monitoring and exhaust nitrogen oxide control. The system and method predicts EONOx sensor signal instability by comparing a calculated pedal based driver demand torque delta to calculated instability thresholds and instability threshold hysteresis margins, and generates instability flags. The system and method further validates any predicted EONOx sensor signal instability by observation. Upon validation of the predicted EONOx sensor signal instability, the system and method latches the EONOx sensor signal status to a stable value.