Downstream Oxygen Sensors No Activity Detected - P0140, P0160

Downstream Oxygen sensors no activity detected - P0140, P0160.
The monitor is single shot monitor (runs once per trip), which is designed to operate only when the sensor has been lit off (up to operating temperature). The monitor can be sub divided into two sections:

Stuck low
(Output voltage < calibrated threshold (0.4 volt).
The monitor initially examines the fuelling control to ensure the system is stable and that linear AFR closed loop control and sub feedback execution has been invoked. Once these conditions are satisfied and a calibrated load/airflow has been achieved, a lean stuck timer is incremented. The monitor then checks the output voltage from the sensor and sets a normal end judgment if a calibrated change in sensor output voltage is observed. If the change in sensor voltage is not detected and the lean stuck timer exceeds the failure threshold, and the associated failure conditions are satisfied, then a failure end judgement is made.

Stuck high
(Output voltage > calibrated threshold (0.4 volt).
Again, the monitor strategy checks for stable AFR control prior to commencing the examination of the sensors output voltage. The monitor then utilises the lean switching characteristics of the sensor during an over-run fuel cut (where the sensors output voltage tends towards 0 volts), to determine it's correct operation. Finally, if the duration of FC exceeds a calibrated period of time and the output voltage of the sensor is greater than calibrated threshold, then a failure judgement is set.