Diagnostic Method

When the oxygen sensor output voltage changes from 0.55 V (rich) to 0.15 V (lean), calculate the minimum response time for output change between 0.5 V and 0.2 V for the judgement criteria.

Fig 1: Rear Oxygen Sensor Voltage Output Graph

Courtesy of SUBARU OF AMERICA, INC.

• Abnormality Judgement 
  1. Judge as NG when the judgement value is larger than the threshold value after deceleration fuel cut. Response time (diagnosis value) Threshold value → abnormal
     NOTE: Variation time of rear oxygen sensor output voltage is short during fuel cut in deceleration. NG judgement should be performed after deceleration fuel cut. Even without deceleration fuel cut, judge as OK if the value is below the threshold.

     When the deceleration fuel cut time is 6000 ms or more, judge as NG if the following criteria are met 2000 ms after recovering from the deceleration fuel cut.

  2. Judge as NG when the oxygen sensor voltage at recovery from a deceleration fuel cut is large.

     If the fuel cut time in a deceleration fuel cut is long (6000 ms or more), and even after recovering from a deceleration fuel cut, the oxygen sensor voltage is high (0.55 V or more), judge as NG.

     Judgement Value 

     JUDGEMENT VALUE REFERENCE
     
     

     Malfunction Criteria	Threshold Value
     Shortest time change from rich (0.5 V O2 output) to lean (0.2 V) when voltage reduces from 0.55 V to 0.15 V	491 ms
     or
     Longest time over 0.55 V	≥ 2000 ms

     Time Needed for Diagnosis:  1 time(s)

     Malfunction Indicator Light Illumination:  Illuminates when malfunction occurs in 2 continuous driving cycles.

• Normality Judgement 
  1. Regardless of a deceleration fuel cut, if the response time (diagnosis value) when the oxygen sensor voltage has changed from rich to lean is shorter than the threshold value (judgement value), judge as a normal condition.

     Response time (diagnosis value) ≤ Threshold value → normal

  2. Do not judge as a normal condition.

     Judge as OK and clear the NG if the following conditions are established.

     Judgement Value 

     JUDGEMENT VALUE REFERENCE
     
     

     Malfunction Criteria	Threshold Value
     Shortest time change from rich (0.5 V O2 output) to lean (0.2 V) when voltage reduces from 0.55 V to 0.15 V	≤ 491 ms

     Time Needed for Diagnosis:  1 time(s)

When the oxygen sensor output voltage changes from 0.25 V (lean) to 0.55 V (rich), calculate the minimum response time for output change between 0.3 V and 0.5 V for the judgement criteria.

Fig 1: Rear Oxygen Sensor Voltage Output Graph

Courtesy of SUBARU OF AMERICA, INC.

• Abnormality Judgement 
  1. Judge as NG when the judgement value is larger than the threshold value after deceleration fuel cut.

     Response time (diagnosis value) Threshold value → abnormal

  2. If the oxygen sensor voltage is small after recovering from a deceleration fuel cut, and remains small, judge as NG.

     Judgement Value 

     JUDGEMENT VALUE REFERENCE
     
     

     Malfunction Criteria	Threshold Value
     Shortest time change from lean (0.3 V O2 output) to rich (0.5 V) when voltage changes from 0.25 V to 0.55 V	2000 ms
     or
     Longest time under 0.25 V	≥ 120000 ms

     Time Needed for Diagnosis:  1 time(s)

     Malfunction Indicator Light Illumination:  Illuminates when malfunction occurs in 2 continuous driving cycles.

• Normality Judgement 
  1. Regardless of a deceleration fuel cut, if the response time (diagnosis value) when the oxygen sensor voltage has changed from rich to lean is shorter than the threshold value (judgement value), judge as a normal condition.

  Response time (diagnosis value) ≤ threshold value → normal

  2. Do not judge as a normal condition.

     Judge as OK and clear the NG if the following conditions are established.

     Judgement Value 

     JUDGEMENT VALUE REFERENCE
     
     

     Malfunction Criteria	Threshold Value
     Shortest time change from lean (0.3 V O2 output) to rich (0.5 V) when voltage changes from 0.25 V to 0.55 V	≤ 2000 ms

     Time Needed for Diagnosis:  1 time(s)