Patent ID: 8863504

Claim:
A method, comprising: determining a first NO x conversion efficiency (η) value; increasing a diesel exhaust fluid (DEF) level of a DEF in a DEF storage source a threshold amount; determining a second NO x conversion η value when the DEF level has increased the threshold amount; determining whether the second NO x conversion η value is at least equal to an emissions compliant NO x conversion η value; and comparing the first NO x conversion η value and the second NO x conversion η value, determining a NO x conversion η change in response to comparing, and determining a DEF quality indicator associated with a NO x reduction capability of the DEF in the DEF storage source in response to the NO x conversion η change, wherein in response to determining the second NO x conversion value is at least equal to the emissions compliant NO x conversion η value and determining the NO x conversion η change is greater than a NO x conversion η change threshold, determining the DEF quality indicator is compliant degraded.