A system includes: a NOx sensor; and a controller configured to: increase an amount of O2 in a chamber of the NOx sensor; interpret one or more values of a parameter indicative an amount of O2 and/or NOx measured by the NOx sensor; determine if the one or more values of the parameter exceed a threshold value; and indicate a failure of the NOx sensor responsive to the one or more values of the parameter do not exceed the threshold value.