Theory Of Operation

The Downstream Oxygen (O2) Sensor no activity diagnostic monitor is intended to diagnose a Downstream O2 Sensor that is not moving or is stuck in a voltage window. This diagnostic is intended to verify the Downstream O2 Sensors ability to respond to fuel adaptation deviations during the Catalyst Monitor test. To pass this monitor, the sensor must output a voltage greater than a high calibrated voltage and less than a low calibrated voltage within a calibrated time period. The test includes a non-intrusive monitor and an intrusive fueling monitor. The intrusive monitor will only run if the non-intrusive test does not pass within the calibrated time period.

The intrusive fueling routine is used to 'jolt' the fuel feedback system to force the monitor to pass. A test failure occurs if the voltage pass values are not achieved after the total accumulated test time.