Conditions for Setting the DTC

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Due to aging and poisoning of the sensor element, the characteristics could change and have to be monitored. Therefore, a self diagnosis is implemented within the sensor control unit which is determining a measurement deviation in relation to a reference point defined during sensor production.

P11D7

The NOx sensor control unit sends a unique message to the ECM upon the self-diagnosis being aborted. The number of aborts is tracked by the ECM. If the number of self diagnostic aborts exceeds a threshold, the DTC is set.

P22FE

The NOx sensor self diagnostic result is received from the NOx sensor control unit and stored in a ring buffer, which takes the average of the last calibrated number of test results and averages them for comparison to an upper and lower calibrated threshold. If the average result is greater than or less than the calibrated thresholds, a NOx sensor self diagnostic fault will set.