Theory Of Operation

For an aged Oxygen (O2) Sensor, the response rate to the air/fuel change is slower than when it was new. The O2 Sensor tends to move less with the same air/fuel changes in a given time frame. Therefore by observing the activity of voltage readings from the O2 Sensor, the quality of the O2 Sensor can be detected.

The Downstream O2 Sensor is located in the exhaust path behind the Catalytic Converter, and is monitored for proper response to assure optimum Catalytic Converter efficiency. This occurs by monitoring the change in the Downstream O2 Sensor voltage over time, when the fuel is shut off during a decel condition after the enable conditions were met. If the slope of the Downstream O2 Sensor is too small, the monitor will fail indicating that the O2 Sensor is not reliable enough to monitor Catalytic Converter efficiency.