known app ref value is used with expression k 6 as described in step 308 to effect a pumping current modification based on the sensor internal reference chamber oxygen partial pressure step 404 activates the pump control mechanism queries the developing sensor nernst voltage and updates the value of app ref based on the applied charge preset in steps 401 and 403 and the aforementioned sensor calibration factor in step 405 a judgment is made as to whether the value of anv is within the nw limit as described in step 206 if the judgment is yes the sensor is considered to be substantially at null and control is passed from method m 400 back to the supervisory program if the judgment is no the sensor is not yet at the null point and control is passed to step 406 in step 406 a judgment is made as to whether the value of anv is less than the mvtrip value as described in step 208 if the judgment is no the dynamic reduction trigger point mvtrip has not been reached and control is passed back to step 403 using the updated value of app ref if the judgment in step 406 is yes then control is passed to the dynamic reduction algorithms of steps 407 through 409 in step 407 the pump current magnitude control variable value is modified as function of two factors k 3 as described in step.