Diagnostic Method

• Output fluctuation accumulate method 

The accumulated value of front A/F sensor output changes and the accumulated value of rear oxygen sensor output changes are determined, and the diagnostic value is calculated using the following formula. Diagnostic value = Accumulated value of rear oxygen sensor output changes / Accumulated value of front A/ F sensor output changes

• For example 
  Fig 1: Front And Rear Oxygen A/ F Sensor Output Waveform

  Courtesy of SUBARU OF AMERICA, INC.

Judge NG when the malfunction criteria below are completed, and judge OK when they are not completed.

• Judgment Value 
  JUDGMENT VALUE
  
  

  Malfunction Criteria	Threshold Value
  Accumulated variation of output Voltage of rear oxygen sensor per 50 milliseconds divided by accumulated Variation of output voltage of front lambda sensor per 50 milliseconds	≥ 1.4

Time Needed for Diagnosis  : 45 seconds

Malfunction Indicator Light Illumination  : 2 continuous driving cycles.