Diagnostic Method

• Intermediate

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 judgment criteria.

Fig 1: Oxygen Sensor Voltage Output Graph

Courtesy of SUBARU OF AMERICA, INC.

• Wide

When the oxygen sensor output voltage changes from 0.65 V (rich) to 0.05 V (lean), calculate the minimum response time for output change between 0.6 V and 0.1 V for the judgment criteria.

Fig 2: Oxygen Sensor Voltage Output Graph

Courtesy of SUBARU OF AMERICA, INC.

• Abnormality Judgment 

1. Judge as NG when the judgment value is larger than the threshold value after deceleration fuel cut. Response time (diagnosis value) > threshold value → abnormal
   NOTE: Perform NG judgment only during fuel cut, when exhaust gas apparently changes from rich → lean. Even without deceleration fuel cut, judge as OK if the value is below the threshold.
2. Judge as NG when the oxygen sensor voltage at a deceleration fuel cut is large.

   Judge as NG when oxygen sensor voltage is large even after a long period of deceleration fuel cut has completed.

   Judgment value (Intermediate) 

   THRESHOLD VALUE
   
   

   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

   Judgment value (Wide) 

   JUDGMENT VALUE
   
   

   Malfunction Criteria	Threshold Value
   Shortest time change from rich (0.6 V O2 output) to lean (0.1 V) when voltage reduces from 0.65 V to 0.05 V	> Value from Map
   or
   Longest time over 0.65 V	≥ 2000 ms

   Map 

   TEMPERATURE SPECIFICATION
   
   

   Estimated temperature of rear oxygen sensor element when fuel cut starts °C (°F)	0 (32)	480 (896)	500 (932)	1000 (1832)
   Longest time in rich status after fuel cut (ms)	3000	3000	2000	2000

   Time Needed for Diagnosis:  1 time(s)

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

• Normality Judgment 

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 (judgment 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.

   Judgment value (Intermediate) 

   JUDGMENT VALUE
   
   

   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

   Judgment value (Wide) 

   JUDGMENT VALUE
   
   

   Malfunction Criteria	Threshold Value
   Shortest time change from rich (0.6 V O2 output) to lean (0.1 V) when voltage reduces from 0.65 V to 0.05 V	≤ 2000 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 judgment criteria.

Fig 1: Oxygen Sensor Voltage Output Graph

Courtesy of SUBARU OF AMERICA, INC.

• Abnormality Judgment 

1. Judge as NG when the judgment 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.

   Judgment Value 

   JUDGMENT VALUE
   
   

   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	> 4000 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 Judgment 

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 (judgment 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.

   Judgment Value 

   JUDGMENT VALUE
   
   

   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	≤ 4000 ms

   Time Needed for Diagnosis:  1 time(s)