We are facing problem with two oxygen sensors which are connected to two LC control units which we installed six months back. Each LC control unit is connected with one oxygen sensor and one hydrogen sensor. Two hydrogen sensors are working good where as we got problem with two oxygen sensors.

We connected connections as mentioned below


Control unit : Port 14 – blue wire of oxygen sensor and port – 15 red wire of oxygen sensor

                    Port 26 – blue wire of hydrogen sensor and port – 27 red wire of hydrogen sensor

The reading of oxygen is 3 to 4% where as it should be above 18%


We tried changing the wires red to 14 and blue to 15 then it is showing 0% or sometimes –ve values.

We also changed sensors channel positions but result is same as before.

We are placing the same problem with two oxygen sensor in two control units.

Did all the calibrations as per calibration certificate given along with sensors.


The sensors appear to be wired correctly (as per: How to wire a 3000SI to a Status Panel), so the likely issue is either calibration or O2 sensor. The sensor reading as low as that after 6 months is strange as the cell output drift is less than 1% per 3 months, but it is possible if the sensors are being exposed to high levels of O2. 

I recommend re-calibration of the Oxygen sensors as per user manual instructions (I suggest a 0% O2 calibration gas like 100% N2 for the zero gas) and as high an O2 concentration as possible (I recommend 100% O2 for the span gas). It is also very important that a zero calibration is carried out prior to a span calibration.

If this does not clear the issue I recommend the oxygen sensors are replaced with new as it is likely they are depleted and are no longer functioning correctly.