Did the probe's display value get corrected using a dew point meter (or thin film carbon determination) method? If so, the issue is not with the oxygen probe. If repeated testing still yields incorrect results (error greater than 15%), the following troubleshooting steps should be performed. Check and confirm that the thermocouple's compensation wire and the oxygen probe's signal line connections are clean and secure, and that they are properly connected to the corresponding terminals on the instrument.