Abstract: A method and an apparatus including a processing circuit structured to: receive a first signal indicative of an upstream air-fuel equivalence ratio from a first sensor positioned upstream of an intake of a catalyst, the first signal defining a duty cycle, receive a second signal indicative of a downstream air-fuel equivalence ratio from a second sensor positioned downstream of the intake of the catalyst, adjust the duty cycle based at least in part on the second signal, and provide a fault signal in response to the duty cycle not meeting a duty cycle range for a predetermined period of time. A notification circuit is structured to provide a notification indicating that the second sensor is faulty in response to receiving the fault signal.

Abstract: An apparatus includes a processing circuit structured to receive a first signal indicative of an upstream air-fuel equivalence ratio from a first sensor positioned upstream of an intake of a catalyst, receive a second signal indicative of a downstream air-fuel equivalence ratio from a second sensor positioned downstream of the intake of the catalyst, determine an actual oxygen storage capacity of the catalyst based at least in part on the received first signal and the received second signal, compare the actual oxygen storage capacity to a maximum storage capacity, and provide a fault signal in response to the actual oxygen storage capacity exceeding the maximum storage capacity. The apparatus also includes a notification circuit structured to provide a notification indicating that the second sensor is faulty in response to receiving the fault signal.

Abstract: An apparatus includes a processing circuit structured to receive a first signal indicative of an upstream air-fuel equivalence ratio from a first sensor positioned upstream of an intake of a catalyst, receive a second signal indicative of a downstream airfuel equivalence ratio from a second sensor positioned downstream of the intake of the catalyst, determine an actual oxygen storage capacity of the catalyst based at least in part on the received first signal and the received second signal, compare the actual oxygen storage capacity to a maximum storage capacity, and provide a fault signal in response to the actual oxygen storage capacity exceeding the maximum storage capacity. The apparatus also includes a notification circuit structured to provide a notification indicating that the second sensor is faulty in response to receiving the fault signal.